string assignment in java

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Java String equals()

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In Java, a string is a sequence of characters. For example, "hello" is a string containing a sequence of characters 'h' , 'e' , 'l' , 'l' , and 'o' .

We use double quotes to represent a string in Java. For example,

Here, we have created a string variable named type . The variable is initialized with the string Java Programming .

Example: Create a String in Java

In the above example, we have created three strings named first , second , and third .

Here, we are directly creating strings like primitive types .

However, there is another way of creating Java strings (using the new keyword).

We will learn about that later in this tutorial.

Note : Strings in Java are not primitive types (like int , char , etc). Instead, all strings are objects of a predefined class named String .

And all string variables are instances of the String class.

Java String Operations

Java provides various string methods to perform different operations on strings. We will look into some of the commonly used string operations.

1. Get the Length of a String

To find the length of a string, we use the length() method. For example,

In the above example, the length() method calculates the total number of characters in the string and returns it.

To learn more, visit Java String length() .

2. Join Two Java Strings

We can join two strings in Java using the concat() method. For example,

In the above example, we have created two strings named first and second . Notice the statement,

Here, the concat() method joins the second string to the first string and assigns it to the joinedString variable.

We can also join two strings using the + operator in Java.

To learn more, visit Java String concat() .

3. Compare Two Strings

In Java, we can make comparisons between two strings using the equals() method. For example,

In the above example, we have created 3 strings named first , second , and third .

Here, we are using the equal() method to check if one string is equal to another.

The equals() method checks the content of strings while comparing them. To learn more, visit Java String equals() .

Note : We can also compare two strings using the == operator in Java. However, this approach is different than the equals() method. To learn more, visit Java String == vs equals() .

Escape Character in Java Strings

The escape character is used to escape some of the characters present inside a string.

Suppose we need to include double quotes inside a string.

Since strings are represented by double quotes , the compiler will treat "This is the " as the string. Hence, the above code will cause an error.

To solve this issue, we use the escape character \ in Java. For example,

Now escape characters tell the compiler to escape double quotes and read the whole text.

Java Strings are Immutable

In Java, strings are immutable . This means once we create a string, we cannot change that string.

To understand it more thoroughly, consider an example:

Here, we have created a string variable named example . The variable holds the string "Hello! " .

Now, suppose we want to change the string.

Here, we are using the concat() method to add another string "World" to the previous string.

It looks like we are able to change the value of the previous string. However, this is not true .

Let's see what has happened here:

• JVM takes the first string "Hello! "
• creates a new string by adding "World" to the first string
• assigns the new string "Hello! World" to the example variable
• The first string "Hello! " remains unchanged

Creating Strings Using the New Keyword

So far, we have created strings like primitive types in Java.

Since strings in Java are objects, we can create strings using the new keyword as well. For example,

In the above example, we have created a string name using the new keyword.

Here, when we create a string object, the String() constructor is invoked.

To learn more about constructors, visit Java Constructor .

Note : The String class provides various other constructors to create strings. To learn more, visit Java String (official Java documentation) .

Example: Create Java Strings Using the New Keyword

Create string using literals vs. new keyword.

Now that we know how strings are created using string literals and the new keyword, let's see what is the major difference between them.

In Java, the JVM maintains a string pool to store all of its strings inside the memory. The string pool helps in reusing the strings.

1. While creating strings using string literals,

Here, we are directly providing the value of the string ( Java ). Hence, the compiler first checks the string pool to see if the string already exists.

• If the string already exists , the new string is not created. Instead, the new reference, example points to the already existing string ( Java ).
• If the string doesn't exist , a new string ( Java) is created.

2. While creating strings using the new keyword,

Here, the value of the string is not directly provided. Hence, a new "Java" string is created even though "Java" is already present inside the memory pool.

• Methods of Java String

Besides those mentioned above, there are various string methods present in Java. Here are some of those methods:

Table of Contents

• Java String
• Create a String in Java
• Get Length of a String
• Join two Strings
• Compare two Strings
• Escape character in Strings
• Immutable Strings
• Creating strings using the new keyword
• String literals vs new keyword

Sorry about that.

Related Tutorials

Java Library

Java String Manipulation: Functions and Methods with EXAMPLE

What are Strings?

A string in literal terms is a series of characters. Hey, did you say characters, isn’t it a primitive data type in Java. Yes, so in technical terms, the basic Java String is basically an array of characters.

So my above string of “ ROSE ” can be represented as the following –

Why use Strings?

One of the primary functions of modern computer science, is processing human language.

Similarly to how numbers are important to math, language symbols are important to meaning and decision making. Although it may not be visible to computer users, computers process language in the background as precisely and accurately as a calculator. Help dialogs provide instructions. Menus provide choices. And data displays show statuses, errors, and real-time changes to the language.

As a Java programmer, one of your main tools for storing and processing language is going to be the String class.

String Syntax Examples

Now, let’s get to some syntax,after all, we need to write this in Java code isn’t it.

String is an array of characters, represented as:

In technical terms, the String is defined as follows in the above example-

Now we always cannot write our strings as arrays; hence we can define the String in Java as follows:

In technical terms, the above is represented as:

The String Class Java extends the Object class.

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String Concatenation:

Concatenation is joining of two or more strings.

Have a look at the below picture-

We have two strings str1 = “Rock” and str2 = “Star”

If we add up these two strings, we should have a result as str3= “RockStar”.

Check the below code snippet,and it explains the two methods to perform string concatenation.

First is using “ concat ” method of String class and second is using arithmetic “+” operator. Both results in the same output

Important Java string methods:

Let’s ask the Java String class a few questions and see if it can answer them:

String “Length” Method

How will you determine the length of given String? I have provided a method called as “ length “. Use it against the String you need to find the length.

Expected Output:

String “indexOf” Method

If I know the length, how would I find which character is in which position? In short, how will I find the index of a character?

You answered yourself, buddy, there is an “indexOf” method that will help you determine the location of a specific character that you specify.

String “charAt” Method

Similar to the above question, given the index, how do I know the character at that location?

Simple one again!! Use the “ charAt ” method and provide the index whose character you need to find.

String “CompareTo” Method

Do I want to check if the String that was generated by some method is equal to something that I want to verify with? How do I compare two Strings?

Use the method “ compareTo ” and specify the String that you would like to compare.

Use “compareToIgnoreCase” in case you don’t want the result to be case sensitive.

The result will have the value 0 if the argument string is equal to this string; a value less than 0 if this string is lexicographically less than the string argument; and a value greater than 0 if this string is lexicographically greater than the string argument.

String “Contain” Method

I partially know what the string should have contained, how do I confirm if the String contains a sequence of characters I specify?

Use the method “ contains ” and specify the characters you need to check.

Returns true if and only if this string contains the specified sequence of char values.

String “endsWith” Method

How do I confirm if a String ends with a particular suffix? Again you answered it. Use the “endsWith” method and specify the suffix in the arguments.

Returns true if the character sequence represented by the argument is a suffix of the character sequence represented by this object.

String “replaceAll” & “replaceFirst” Method

I want to modify my String at several places and replace several parts of the String?

Java String Replace, replaceAll and replaceFirst methods. You can specify the part of the String you want to replace and the replacement String in the arguments.

String Java “tolowercase” & Java “touppercase” Method

I want my entire String to be shown in lower case or Uppercase?

Just use the “toLowercase()” or “ToUpperCase()” methods against the Strings that need to be converted.

Important Points to Note:

• String is a Final class ; i.e once created the value cannot be altered. Thus String objects are called immutable.
• The Java Virtual Machine(JVM) creates a memory location especially for Strings called String Constant Pool . That’s why String can be initialized without ‘new’ keyword.
• String class falls under java.lang.String hierarchy . But there is no need to import this class. Java platform provides them automatically.
• String reference can be overridden but that does not delete the content ; i.e., if

String h1 = “hello”;

h1 = “hello”+”world”;

then “hello” String does not get deleted. It just loses its handle.

• Multiple references can be used for same String but it will occur in the same place ; i.e., if

String h2 = “hello”;

String h3 = “hello”;

then only one pool for String “hello” is created in the memory with 3 references-h1,h2,h3

• If a number is quoted in ” “ then it becomes a string , not a number anymore. That means if

String S1 =”The number is: “+ “123”+”456″;

System. out .println(S1);

then it will print: The number is: 123456

If the initialization is like this:

String S1 = “The number is: “+(123+456);

System.out.println(S1);

then it will print: The number is:579

That’s all to Strings!

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Class String

• java.lang.Object
• java.lang.String

String str = "abc";

char data[] = {'a', 'b', 'c'}; String str = new String(data);

System.out.println("abc"); String cde = "cde"; System.out.println("abc" + cde); String c = "abc".substring(2,3); String d = cde.substring(1, 2);

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang. Object

Methods inherited from interface java.lang. charsequence, field detail, case_insensitive_order, constructor detail.

c == (char)(((hibyte & 0xff) << 8) | ( b & 0xff))

Method Detail

Codepointat, codepointbefore, codepointcount, offsetbycodepoints.

dstBegin + (srcEnd-srcBegin) - 1

• dstBegin+(srcEnd-srcBegin) is larger than dst.length

contentEquals

Equalsignorecase.

• Applying the method Character.toLowerCase(char) to each character produces the same result Parameters: anotherString - The String to compare this String against Returns: true if the argument is not null and it represents an equivalent String ignoring case; false otherwise See Also: equals(Object)

this.charAt(k)-anotherString.charAt(k)

this.length()-anotherString.length()

compareToIgnoreCase

Regionmatches.

• There is some nonnegative integer k less than len such that: this.charAt(toffset + k ) != other.charAt(ooffset + k ) Parameters: toffset - the starting offset of the subregion in this string. other - the string argument. ooffset - the starting offset of the subregion in the string argument. len - the number of characters to compare. Returns: true if the specified subregion of this string exactly matches the specified subregion of the string argument; false otherwise.

this.charAt(toffset+k) != other.charAt(ooffset+k)

Character.toLowerCase(this.charAt(toffset+k)) != Character.toLowerCase(other.charAt(ooffset+k))

Character.toUpperCase(this.charAt(toffset+k)) != Character.toUpperCase(other.charAt(ooffset+k))

s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]

this.charAt( k ) == ch

this.codePointAt( k ) == ch

(this.charAt( k ) == ch) && ( k >= fromIndex)

(this.codePointAt( k ) == ch) && ( k >= fromIndex)

lastIndexOf

(this.charAt( k ) == ch) && ( k <= fromIndex)

(this.codePointAt( k ) == ch) && ( k <= fromIndex)

this.startsWith(str, k )

k >= fromIndex && this.startsWith(str, k )

k <= fromIndex && this.startsWith(str, k )

"unhappy".substring(2) returns "happy" "Harbison".substring(3) returns "bison" "emptiness".substring(9) returns "" (an empty string)

"hamburger".substring(4, 8) returns "urge" "smiles".substring(1, 5) returns "mile"

subSequence

str.subSequence(begin, end)

str.substring(begin, end)

"cares".concat("s") returns "caress" "to".concat("get").concat("her") returns "together"

"mesquite in your cellar".replace('e', 'o') returns "mosquito in your collar" "the war of baronets".replace('r', 'y') returns "the way of bayonets" "sparring with a purple porpoise".replace('p', 't') returns "starring with a turtle tortoise" "JonL".replace('q', 'x') returns "JonL" (no change)

Pattern . matches( regex , str )

replaceFirst

Pattern . compile ( regex ). matcher ( str ). replaceFirst ( repl )

Pattern . compile ( regex ). matcher ( str ). replaceAll ( repl )

Regex Limit Result : 2 { "boo", "and:foo" } : 5 { "boo", "and", "foo" } : -2 { "boo", "and", "foo" } o 5 { "b", "", ":and:f", "", "" } o -2 { "b", "", ":and:f", "", "" } o 0 { "b", "", ":and:f" }

Pattern . compile ( regex ). split ( str ,  n )

Regex Result : { "boo", "and", "foo" } o { "b", "", ":and:f" }

For example, String message = String.join("-", "Java", "is", "cool"); // message returned is: "Java-is-cool"

For example, List<String> strings = new LinkedList<>(); strings.add("Java");strings.add("is"); strings.add("cool"); String message = String.join(" ", strings); //message returned is: "Java is cool" Set<String> strings = new LinkedHashSet<>(); strings.add("Java"); strings.add("is"); strings.add("very"); strings.add("cool"); String message = String.join("-", strings); //message returned is: "Java-is-very-cool"

toLowerCase

toUpperCase

toCharArray

Copyvalueof.

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Programming & Frameworks

String in java – string functions in java with examples.

What is a Java String?

In Java, a string is an object that represents a sequence of characters or char values. The java.lang.String class is used to create a Java string object.

There are two ways to create a String object:

• By string literal : Java String literal is created by using double quotes. For Example: String s= “Welcome” ;  
• By new keyword : Java String is created by using a keyword “new”. For example:  String s= new String( “Welcome” );   It creates two objects (in String pool and in heap) and one reference variable where the variable ‘s’ will refer to the object in the heap.

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Now, let us understand the concept of Java String pool.

Java String Pool: Java String pool refers to collection of Strings which are stored in heap memory. In this, whenever a new object is created, String pool first checks whether the object is already present in the pool or not. If it is present, then same reference is returned to the variable else new object will be created in the String pool and the respective reference will be returned. Refer to the diagrammatic representation for better understanding:

Before we go ahead, One key point I would like to add that unlike other data types in Java, Strings are immutable. By immutable, we mean that Strings are constant, their values cannot be changed after they are created. Because String objects are immutable, they can be shared. For example:

   String str =”abc”; is equivalent to :

  ch ar data[] = {‘a’, ‘b’, ‘c’};     String str = new String(da ta);

Let us now look at some of the inbuilt methods in String class .

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Java S tring Methods

• Java String length() :  The Java String length() method tells the length of the string. It returns count of total number of characters present in the String. For exam p le:

Here, String length()  function will return the length 5 for s1 and 7 for s2 respectively.

• Java St ring comp areTo () : This method compares the given string with current string. It is a method of  ‘Comparable’  interface which is implemented by String class. Don’t worry, we will be learning about String interfaces later. It either returns positive number, negative number or 0.  For example:

This program shows the comparison between the various string. It is noticed that   i f s 1 > s2 ,  it  returns a positive number   i f   s1 < s 2 , it returns a negative number  i f s1 == s2, it returns 0

• Java String IsEmpty() : This method checks whether the String contains anything or not. If the java String is Empty, it returns true else false. For example: public class IsEmptyExample{ public static void main(String args[]){ String s1=""; String s2="hello"; System.out.println(s1.isEmpty()); // true System.out.println(s2.isEmpty()); // false }}
• Java String ValueOf() : This method converts different types of values into string.Using this method, you can convert int to string, long to string, Boolean to string, character to string, float to string, double to string, object to string and char array to string. The signature or syntax of string valueOf() method is given below: public static String valueOf(boolean b) public static String valueOf(char c) public static String valueOf(char[] c) public static String valueOf(int i) public static String valueOf(long l) public static String valueOf(float f) public static String valueOf(double d) public static String valueOf(Object o)

Let’s understand this with a programmatic example:

In the above code, it concatenates the Java String and gives the output – 2017.

Java String replace() : The Java String replace() method returns a string, replacing all the old characters or CharSequence to new characters. There are 2 ways to replace methods in a Java String. 

In the above code, it will replace all the occurrences of ‘h’ to ‘t’. Output to the above code will be “tello tow are you”.  Let’s see the another type of using replace method in java string: Java String replace(CharSequence target, CharSequence replacement) method :

In the above code, it will replace all occurrences of “Edureka” to “Brainforce”. Therefore, the output would be “ Hey, welcome to Brainforce”.

In the above code, the first two statements will return true as it matches the String whereas the second print statement will return false because the characters are not present in the string.

• Java String equals() : The Java String equals() method compares the two given strings on the basis of content of the string i.e Java String representation. If all the characters are matched, it returns true else it will return false. For example: public class EqualsExample{ public static void main(String args[]){ String s1="hello"; String s2="hello"; String s3="hi"; System.out.println(s1.equalsIgnoreCase(s2)); // returns true System.out.println(s1.equalsIgnoreCase(s3)); // returns false } }

In the above code, the first statement will return true because the content is same irrespective of the case. Then, in the second print statement will return false as the content doesn’t match in the respective strings.

• Java String IsEmpty() : This method checks whether the String is empty or not. If the length of the String is 0, it returns true else false. For example: 

In the above code, the first print statement will return true as it does not contain anything while the second print statement will return false.

• Java String endsWith() : The Java String endsWith() method checks if this string ends with the given suffix. If it returns with the given suffix, it will return true else returns fals e. F or example:

This is not the end. There are more Java String methods that will help you make your code simpler.  

Moving on, Java String class implements three  interfac es , namely – Serializable, Comparable and C h arSequence .

• StringBuffer and StringBuilder are mutable classes. StringBuffer operations are thread-safe and synchronized whereas StringBuilder operations are not thread-safe.
• StringBuffer is to be used when multiple threads are working on same String and StringBuilder in the single threaded environment.
• StringBuilder performance is faster when compared to StringBuffer because of no overhead of synchronized.

I hope you guys are clear with Java String, how they are created, their different methods and interfaces. I would recommend you to try all the examples.  Do read my next blog on Java Interview Questions which will help you set apart in the interview process. If you’re just beginning, then watch at this Java Tutorial to Understand the Fundamental Java Concepts.

Now that you have understood basics of Java, check out the Java Online Course by Edureka, a trusted online learning company with a network of more than 250,000 satisfied learners spread across the globe. Edureka’s Java J2EE and SOA training and certification course is designed for students and professionals who want to be a Java Developer. The course is designed to give you a head start into Java programming and train you for both core and advanced Java concepts along with various Java frameworks like Hibernate & Spring.

Got a question for us? Please mention it in the comments section of this blog  and we will get back to you.

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This is wrong information. Please correct it.

( Corrections are in bold letters) By new keyword : Java String is created by using a keyword “new”. For example: String s=new String(“Welcome”); It creates two objects ( in String pool and in heap ) and one reference variable where the variable ‘s’ will refer to the object in the heap.

Please refer to Java 8 reference books, There are changes in version of java 8.

Hello, Nice Blog, But please change the image where you are comparing two string using == there you should modify the last image as s1 == s3 Sandeep Patidar

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Java String: Exercises, Practice, Solution

Java string exercises [112 exercises with solution].

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1. Write a Java program to get the character at the given index within the string.

Sample Output:

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2. Write a Java program to get the character (Unicode code point) at the given index within the string.

3. Write a Java program to get the character (Unicode code point) before the specified index within the string.

4. Write a Java program to count Unicode code points in the specified text range of a string.

5. Write a Java program to compare two strings lexicographically. Two strings are lexicographically equal if they are the same length and contain the same characters in the same positions.

6. Write a Java program to compare two strings lexicographically, ignoring case differences.

7. Write a Java program to concatenate a given string to the end of another string.

8. Write a Java program to test if a given string contains the specified sequence of char values.

9. Write a Java program to compare a given string to the specified character sequence.

10. Write a Java program to compare a given string to a specified string buffer.

11. Write a Java program to create a String object with a character array.

12. Write a Java program to check whether a given string ends with another string.

13. Write a Java program to check whether two String objects contain the same data.

14. Write a Java program to compare a given string to another string, ignoring case considerations.

15. Write a Java program to print the current date and time in the specified format.

16. Write a Java program to get the contents of a given string as a byte array.

17. Write a Java program to get the contents of a given string as a character array.

18. Write a Java program to create a distinct identifier for a given string.

19. Write a Java program to get the index of all the characters of the alphabet.

Sample string of all alphabet: "The quick brown fox jumps over the lazy dog."

20. Write a Java program to get the Canonical representation of the string object.

21. Write a Java program to get the last index of a string within a string.

22. Write a Java program to get the length of a given string.

23. Write a Java program to find out whether a region in the current string matches a region in another string.

24. Write a Java program to replace a specified character with another character.

25. Write a Java program to replace each substring of a given string that matches the given regular expression with the given replacement.

Sample string : "The quick brown fox jumps over the lazy dog."

In the above string replace all the fox with cat.

26. Write a Java program to check whether a given string starts with another string.

27. Write a Java program to get a substring of a given string at two specified positions.

28. Write a Java program to create a character array containing a string.

29. Write a Java program to convert all characters in a string to lowercase.

30. Write a Java program to convert all characters in a string to uppercase.

31. Write a Java program to trim leading or trailing whitespace from a given string.

32. Write a Java program to find the longest Palindromic Substring within a string.

33. Write a Java program to find all interleavings of given strings.

34. Write a Java program to find the second most frequent character in a given string.

35. Write a Java program to print all permutations of a given string with repetition.

36. Write a Java program to check whether two strings interlive of a given string. Assuming that unique characters are present in both strings.

37. Write a Java program to find the length of the longest substring of a given string without repeating characters.

38. Write a Java program to print the result of removing duplicates from a given string.

39. Write a Java program to find the first non-repeating character in a string.

40. Write a Java program to divide a string into n equal parts.

41. Write a Java program to remove duplicate characters from a given string that appear in another given string.

42. Write a Java program to print a list of items containing all characters of a given word.

43. Write a Java program to find the character in a string that occurs the most frequently.

44. Write a Java program to reverse a string using recursion.

45. Write a Java program to reverse words in a given string.

46. Write a Java program to reverse every word in a string using methods.

47. Write a Java program to rearrange a string so that the same characters are positioned a distance away.

48. Write a Java program to remove "b" and "ac" from a given string.

49. Write a Java program to find the first non-repeating character from a stream of characters.

50. Write a Java program to find the lexicographic rank of a given string.

N.B.: Total possible permutations of BDCA are(lexicographic order) : ABCD ABDC ACBD ACDB ADBC ADCB BACD BADC BCAD BCDA BDAC BDCA 1   2   3   4   5   6   7   8   9   10   11   12 The BDCA appear in 12 position of permutation (lexicographic order).

51. Write a Java program to count and print all duplicates in the input string.

52. Write a Java program to check if two given strings are rotations of each other.

53. Write a Java program to match two strings where one string contains wildcard characters.

54. Write a Java program to find the smallest window in a string containing all characters in another string.

55. Write a Java program to remove all adjacent duplicates recursively from a given string.

56. Write a Java program that appends two strings, omitting one character if the concatenation creates double characters.

57. Write a Java program to create a string from a given string by swapping the last two characters of the given string. The string length must be two or more.

58. Write a Java program to read a string and return true if it ends with a specified string of length 2.

59. Write a Java program to read a string. If the string begins with "red" or "black" return that color string, otherwise return the empty string.

60. Write a Java program to read two strings append them together and return the result. If the strings are different lengths, remove characters from the beginning of the longer string and make them equal lengths.

61. Write a Java program to create a new string taking specified number of characters from first and last position of a given string.

62. Write a Java program to read a string and return true if "good" appears starting at index 0 or 1 in the given string.

63. Write a Java program to check whether the first two characters appear at the end of a given string.

64. Write a Java program to read a string. If a substring of length two appears at both its beginning and end, return a string without the substring at the beginning; otherwise, return the original string unchanged.

65. Write a Java program to read a given string and return the string without the first or last characters if they are the same, otherwise return the string without the characters.

66. Write a Java program to read a string and return it without the first two characters. Keep the first character if it is 'g' and keep the second character if it is 'h'.

67. Write a Java program to read a string and remove the first two characters if one or both are equal to a specified character, otherwise leave them unchanged.

68. Write Java program to read a string and return after removing specified characters and their immediate left and right adjacent characters.

69. Write a Java program to return the substring that is between the first and last appearance of the substring 'toast' in the given string, or return an empty string if the substring 'toast' does not exist.

70. Write a Java program that checks if a string has pq-balance if it contains at least one 'q' directly after each ‘p’. But a 'q' before the 'p' invalidates pq-balance.

71. Write a Java program to check two given strings whether any of them appears at the end of the other string (ignore case sensitivity).

72. Write a Java program to return true if a given string contains the string 'pop', but the middle 'o' also may contain another character.

73. Write a Java program to check whether a substring appears before a period(.) within a given string.

74. Write a Java program to check whether a prefix string created using the first specific character in a given string appears somewhere else in the string.

75. Write a Java program to check whether a given substring appears in the middle of another string. Here middle means the difference between the number of characters to the left and right of the given substring is not more than 1.

76. Write a Java program to count how many times the substring 'life' appears anywhere in a given string. Counting can also happen with the substring 'li?e', any character instead of 'f'.

77. Write a Java program to add a string with a specific number of times separated by a substring.

78. Write a Java program to repeat a specific number of characters for a specific number of times from the last part of a given string.

79. Write a Java program to create a string from a given string. This is done after removing the 2nd character from the substring of length three starting with 'z' and ending with 'g' presents in the said string.

80. Write a Java program to check whether the character immediately before and after a specified character is the same in a given string.

81. Write a Java program to check whether two strings of length 3 and 4 appear the same number of times in a given string.

82. Write a Java program to create a string containing every character twice of a given string.

83. Write a Java program to create a string from two given strings. This is so that each character of the two strings appears individually in the created string.

84. Write a Java program to make an original string made of p number of characters from the first character in a given string. This is followed by p-1 number of characters till p is greater than zero.

85. Write a Java program to make up a string with each character before and after a non-empty substring whichever it appears in a non-empty given string.

86. Write a Java program to count the number of triples (characters appearing three times in a row) in a given string.

87. Write a Java program to check whether a specified character is happy or not. A character is happy when the same character appears to its left or right in a string.

88. Write a Java program to return a string where every appearance of the lowercase word 'is' has been replaced with 'is not'.

89. Write a Java program to calculate the sum of the numbers that appear in a given string.

90. Write a Java program to check the number of times the two substrings appearing anywhere in a string.

91. Write a Java program to count the number of words ending in 'm' or 'n' (not case sensitive) in a given text.

92. Write a Java program that returns a substring after removing all instances of remove string as given from the given main string.

93. Write a Java program to find the longest substring that appears at both ends of a given string.

94. Write a Java program to find the longest mirror image string at both ends of a given string.

95. Write a Java program to return the sum of the digits present in the given string. In the absence of digits, the sum is 0.

96. Write a Java program to create a new string after removing a specified character from a given string. This is except the first and last position.

97. Write a Java program to return a string with characters at index positions 0,1,2,5,6,7, ... from a given string.

98. Write a Java program to check whether the first instance of a given character is immediately followed by the same character in a given string.

99. Write a Java program to return an updated string using every character of even position from a given string.

100. Write a Java program to check if a given string contains another string. Returns true or false.

101. Write a Java program to test if a string contains only digits. Returns true or false.

102. Write a Java program to convert a given string to int, long, floating and double.

103. Write a Java program to remove a specified character from a given string.

104. Write a Java program to sort in ascending and descending order by the length of the given array of strings.

105. Write a Java program to count the occurrences of a given string in another given string.

106. Write a Java program to concatenate a given string with itself a given number of times.

107. Write a Java program to count occurrences of a certain character in a given string.

108. Write a Java program to check whether there are two consecutive (following each other continuously), identical letters in a given string.

109. Write a Java program that reverses all odd-length words in a string.

110. Write a Java program to count the number of characters (alphanumeric only) that occur more than twice in a given string.

111. Write a Java program that removes a specified word from given text. Return the updated string..

112. A string is created by using another string's letters. Letters are case sensitive. Write a Java program that checks the letters of the second string are present in the first string. Return true otherwise false.

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String Arrays in Java

In programming, an array is a collection of the homogeneous types of data stored in a consecutive memory location and each data can be accessed using its index. 

In the Java programming language, we have a String data type. The string is nothing but an object representing a sequence of char values. Strings are immutable in java. Immutable means strings cannot be modified in java.

When we create an array of type String in Java, it is called String Array in Java.

To use a String array, first, we need to declare and initialize it. There is more than one way available to do so.

Declaration:

The String array can be declared in the program without size or with size. Below is the code for the same –  

In the above code, we have declared one String array (myString0) without the size and another one(myString1) with a size of 4. We can use both of these ways for the declaration of our String array in java.

Initialization:

In the first method , we are declaring the values at the same line. A second method is a short form of the first method and in the last method first, we are creating the String array with size after that we are storing data into it.

To iterate through a String array we can use a looping statement.

Time Complexity: O(N), where N is length of array. Auxiliary Space: O(1)

So generally we are having three ways to iterate over a string array.  The first method is to use a for-each loop. The second method is using a simple for loop and the third method is to use a while loop. You can read more about iterating over array from Iterating over Arrays in Java

To find an element from the String Array we can use a simple linear search algorithm. Here is the implementation for the same –

In the above code, we have a String array that contains three elements Apple, Banana & Orange. Now we are searching for the Banana. Banana is present at index location 1 and that is our output.

Sorting of String array means to sort the elements in ascending or descending lexicographic order.

We can use the built-in sort() method to do so and we can also write our own sorting algorithm from scratch but for the simplicity of this article, we are using the built-in method.

Here our String array is in unsorted order, so after the sort operation the array is sorted in the same fashion we used to see on a dictionary or we can say in lexicographic order.

String array to String:

To convert from String array to String, we can use a toString() method.

Here the String array is converted into a string and it is stored into a string type variable but one thing to note here is that comma(,) and brackets are also present in the string. To create a string from a string array without them, we can use the below code snippet.

In the above code, we are having an object of the StringBuilder class. We are appending that for every element of the string array (myarr). After that, we are storing the content of the StringBuilder object as a string using the toString() method.

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Java methods, java classes, java file handling, java how to's, java reference, java examples, java operators.

Operators are used to perform operations on variables and values.

In the example below, we use the + operator to add together two values:

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Although the + operator is often used to add together two values, like in the example above, it can also be used to add together a variable and a value, or a variable and another variable:

Java divides the operators into the following groups:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Logical operators
• Bitwise operators

Arithmetic Operators

Arithmetic operators are used to perform common mathematical operations.

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Java Assignment Operators

Assignment operators are used to assign values to variables.

In the example below, we use the assignment operator ( = ) to assign the value 10 to a variable called x :

The addition assignment operator ( += ) adds a value to a variable:

A list of all assignment operators:

Java Comparison Operators

Comparison operators are used to compare two values (or variables). This is important in programming, because it helps us to find answers and make decisions.

The return value of a comparison is either true or false . These values are known as Boolean values , and you will learn more about them in the Booleans and If..Else chapter.

In the following example, we use the greater than operator ( > ) to find out if 5 is greater than 3:

Java Logical Operators

You can also test for true or false values with logical operators.

Logical operators are used to determine the logic between variables or values:

Java Bitwise Operators

Bitwise operators are used to perform binary logic with the bits of an integer or long integer.

Note: The Bitwise examples above use 4-bit unsigned examples, but Java uses 32-bit signed integers and 64-bit signed long integers. Because of this, in Java, ~5 will not return 10. It will return -6. ~00000000000000000000000000000101 will return 11111111111111111111111111111010

In Java, 9 >> 1 will not return 12. It will return 4. 00000000000000000000000000001001 >> 1 will return 00000000000000000000000000000100

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Multiply 10 with 5 , and print the result.

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1. Overview

In Java, working with arrays is a common task when dealing with collections of data. Sometimes, we may find ourselves in situations where we need to remove all elements from a String array. This task is straightforward, though it requires us to consider how arrays work in Java.

In this quick tutorial, let’s explore how to remove all elements from a String array.

2. Introduction to the Problem

Removing all elements from an array can be helpful in cleaning up data or resetting the array for new input. Before we dive into the implementations, let’s quickly understand how arrays work in Java.

Arrays in Java are fixed in size. In other words, once we create an array, we cannot change its length. This characteristic impacts how we handle operations like “removing” or “inserting” elements, which is not as simple as in Collections like ArrayList .

When we talk about removing all elements from a String array, we have two options:

• Reinitialize a new array (Depending on the requirement, the new array can be empty or the same size.)
• Reset all elements in the array to null values.

Next, let’s take a closer at these two approaches. For simplicity, we’ll leverage unit test assertions to verify if each approach works as expected.

3. Non-Final Array Variable: Reinitializing and Reassignment

The idea of this approach is pretty straightforward. Let’s say we have one array variable,  myArray , containing some elements. To empty myArray , we can reinitialize an empty array and reassign it to the myArray variable.

Next, let’s understand how it works through an example:

In this example, we’re creating a new array of size 0 and assigning it back to myArray1 . This effectively removes all elements by creating an entirely new, empty array.

Sometimes, we want the new array to have the same length as the original one. In this case, we can initialize the new array with the desired size:

As the test shows, the new array has the same size (6) as the original one, and all elements are null values.

Removing all elements by reinitializing and reassignment is straightforward. This approach is useful if we want to completely reset the array and potentially use a different size . However, since we need to assign the new array back to the same variable, this approach works only if the array variable isn’t  final .

Next, let’s explore how to remove all array elements if the array variable is declared as final .

4. Resetting All Elements to null

We’ve mentioned that arrays in Java are fixed in size. That is to say, when an array has been initialized and assigned to a final variable, we cannot remove its elements to get an empty array ( length=0 ) .

One approach to “removing” elements from an array is to set each element to null . This method doesn’t change the array’s size but effectively clears its content.

Next, let’s check an example:

As the above example shows, we loop through myArray and assign a null to each element. After running the loop, the array myArray will still have the same length, but all its elements will be null .

5. Using the Arrays.fill() Method

Java’s Arrays class provides a convenient fill() method that allows us to set all elements of an array to a specific value . We can use this method to set all elements to null , similar to the resetting in loop approach, but with less code:

As we can see, using the Arrays.fill() method , we can achieve array resetting with a single line of code, making it more concise.

6. Conclusion

Removing all elements from an array in Java is a common task when working with arrays, and it can be done in several ways.

In this article, we’ve explored three different approaches to achieve that through examples:

• Reinitializing the array – This is ideal when we want to start fresh with a new array, possibly of a different size. However, it only works for non-final array variables.
• Resetting to null – This is appropriate to clear the content but maintain the array size for future use.
• Using Arrays.fill() – A clean and concise way to reset all elements when maintaining array size.

By understanding the available options, we can choose the best approach for our specific situation, ensuring our code is efficient and clear.

As always, the complete source code for the examples is available over on GitHub .

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Java: assign String[] array element to a String?

I'm pretty new at this, and this is probably a pretty obvious answer. In my csv script, i'm trying to figure out how to read a csv file using the CSVReader class and write to a new csv file. The error is telling me writeNext(java.lang.String[]) cannot be applied to (java.lang.String). I've tried using a direct assignment and getString() method however nothing works. Any ideas?

I have the following code: UPDATED

Error: c:\java\examples\ETHImport.java:46: cannot find symbo symbol : variable newRow location: class ETHImport writer2.writeAll(newRow);

Thanks in advance.

• I'm tired and lazy and don't care enough to do everything for you: where does the error occur? –  Pesto Commented May 27, 2009 at 20:01
• In your new code, you're simply missing "new". It should be "String [] newRow = new String[] ..." –  Michael Myers ♦ Commented May 27, 2009 at 20:58
• cool.. that really helped..not sure why i'm getting a on the variable thats declared in the while loop –  phill Commented May 27, 2009 at 21:05
• See the comment in my answer - you need writer2.writeNext(newRow) inside the loop. Remove the line outside it. –  Jon Skeet Commented May 27, 2009 at 21:54

4 Answers 4

You need a string array, not a single string. Are you really sure you want to pull all the values into a single string to start with? I'd expect writeNext to write a single line based on the string values you give it, with it putting in the commas etc. After all, it's a CsvWriter - it should be doing the comma separating.

It looks to me like the writeAll method you're already using does what you want it to, and writeNext will just write a single line... what are you trying to achieve that writeAll doesn't do for you? Why do you need to read it line by line and construct entries in the first place? Can't you just call:

My guess is that's going to write a tab -separated file though, given how writer2 is constructed.

EDIT: Given the additional information in the comments, I suspect you want to:

• Open a CsvReader
• Open a CsvWriter (with an appropriate Writer and ; as the constructor arguments)
• Loop reading a line at a time as a string array (using CsvReader.readNext() ), creating a new string array for the output, and then calling CsvWriter.writeNext() to write that string array out to the file.
• Close the CsvReader and CsvWriter in finally blocks (so they'll still get closed if anything goes wrong)

Building the new string array from the existing one would be something like (following your example):

That would basically just keep the first three columns, switching round the second and third ones. If you need other columns, just change it in the same kind of way.

Note that I wouldn't recommend using FileWriter to write to a file - use a FileOutputStream and an OutputStreamWriter chained onto it, as this lets you set the character encoding instead of using the platform default one.

• I'm pretty sure you're right. The Javadoc for CsvWriter agrees with your expectation, but I haven't ever used it. –  Matt K Commented May 27, 2009 at 20:04
• the goal is to extract a select number of columns in the csv file, manipulate/format some of them and then insert them into an output file with commas and using a semicolon as a line terminator. The writeall just dumps everything out rather than just outputing the columns i need –  phill Commented May 27, 2009 at 20:15
• I updated it with the suggested changes however i'm resulting in a different error now. It is saying '.class' is expected and there is an carrot pointing to nextLine.. Is it correct syntax to declare a string like this in a while loop? –  phill Commented May 27, 2009 at 20:54
• I'm not sure why you've got an error like that, but you're trying to use newRow outside the loop. You should be calling writer2.writeNext(newRow); inside the loop. –  Jon Skeet Commented May 27, 2009 at 21:46

It is expecting an array of entries rather than just one String. If you are following this example http://opencsv.sourceforge.net/ notice that

the split call at the end results in a String[].

for your code:

• what i'm struggling with is just building a string with selected columns for each recordset so i can write it to a new file –  phill Commented May 27, 2009 at 20:17
• You shouldn't be building a string. You should be building a string array with the selected columns. –  Jon Skeet Commented May 27, 2009 at 20:22
• awesome! I didn't know i could declare something in a method. thanks! –  phill Commented May 27, 2009 at 21:16

To easily put a String into a String[] use:

or the shortcut

Now entriesArr is a String[] containing one element, entries .

• Or the shortcut, as this is a declaration: String[] strs = { str }; –  Tom Hawtin - tackline Commented May 27, 2009 at 21:19
• Note that the element should be a String literal value, so actually the line should be String[] entriesArr = new String[] {"entries"}. –  portfoliobuilder Commented Feb 12, 2015 at 0:42

writer.writeNext(String[]) is looking for an array that it will then write as "[0],[1],[2]"

Since you are storing the entire csv file as one string, you need to split that string backup. Really you should instead not combine every item into one string but instead store it as an array of strings representing each individual line in the csv file.

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