String Class in Java

Last Updated : 01 May, 2025

A string is a sequence of characters. In Java, objects of the String class are immutable, which means they cannot be changed once created. In this article, we are going to learn about the String class in Java.

Example of String Class in Java:

Java

// Java Program to Create a String
import java.io.*;

class Geeks {
    public static void main (String[] args) {
      
      	// String literal
    	String s = "Geeks for Geeks String in Java";
 
      	System.out.println(s);
    }
}

Output

Geeks for Geeks String in Java

Explanation:

The above program creates a string using a literal and prints it.

Table of Content

Creating a String

1. Using String literal
2. Using new keyword

String Constructors in Java
String Methods in Java
Example of String Constructor and String Methods

Creating a String

There are two ways to create string in Java:

1. Using String literal

String s = “GeeksforGeeks”;

2. Using new keyword

String s = new String (“GeeksforGeeks”);

Example of Creating String in Java

Java

// Java Program to Create a String
import java.io.*;

class Geeks {
    public static void main (String[] args) {
      
      	// String literal
    	String s1="String1";
      	System.out.println(s1);
      
      	// Using new Keyword 
      	String s2= new String("String2");
      	System.out.println(s2);
    }
}

Output

String1
String2

String Constructors in Java

String Constructors	Description
String(byte[] byte_arr)	Construct a new String by decoding the byte array. It uses the platform's default character set for decoding.
String(byte[] byte_arr, Charset char_set)	Construct a new String by decoding the byte array. It uses the char_set for decoding.
String(byte[] byte_arr, int start_index, int length)	Construct a new string from the bytes array depending on the start_index(Starting location) and length(number of characters from starting location).
String(byte[] byte_arr, int start_index, int length, Charset char_set)	Construct a new string from the bytes array depending on the start_index(Starting location) and length(number of characters from starting location).Uses char_set for decoding.
String(char[] char_arr)	Allocates a new String from the given Character array.
String(char[] char_array, int start_index, int count)	Allocates a String from a given character array but choose count characters from the start_index.
String(int[] uni_code_points, int offset, int count)	Allocates a String from a uni_code_array but choose count characters from the start_index.
String(StringBuffer s_buffer)	Allocates a new string from the string in s_buffer.
String(StringBuilder s_builder)	Allocates a new string from the string in s_builder.

Let us check these constructors using a example demonstrating the use of them.

Example String Constructor in Java

Java

// Java Program to implement String Constructor
import java.nio.charset.Charset;

class Geeks {
    
    // Variables in Methods
    static byte[] b_arr = {71, 101, 101, 107, 115};
    static Charset cs = Charset.defaultCharset();
    static char[] char_arr = {'G', 'e', 'e', 'k', 's'};
    static int[] uni_code = {71, 101, 101, 107, 115};
    static StringBuffer s_buffer = new StringBuffer("Geeks");
    static StringBuilder s_builder = new StringBuilder("Geeks");

    public static void main(String[] args) {
        
        // Method 1
        String s1 = new String(b_arr);
        System.out.println("Method 1: " + s1);
        System.out.println();

        // Method 2
        String s2 = new String(b_arr, cs);
        System.out.println("Method 2: " + s2);
        System.out.println();

        // This is alternative way for Method 2
        String s3 = new String(b_arr, Charset.forName("US-ASCII"));
        System.out.println("Method 2 Alternative: " + s3);
        System.out.println();

        // Method 3
        String s4 = new String(b_arr, 1, 3);
        System.out.println("Method 3: " + s4);
        System.out.println();

        // Method 4
        String s5 = new String(b_arr, 1, 3, cs);
        System.out.println("Method 4: " + s5);
        System.out.println();

        // This is alternative way for Method 4
        String s6 = new String(b_arr, 1, 4, Charset.forName("US-ASCII"));
        System.out.println("Method 4 Alternative: " + s6);
        System.out.println();

        // Method 5
        String s7 = new String(char_arr);
        System.out.println("Method 5: " + s7);
        System.out.println();

        // Method 6
        String s8 = new String(char_arr, 1, 3);
        System.out.println("Method 6: " + s8);
        System.out.println();

        // Method 7
        String s9 = new String(uni_code, 1, 3);
        System.out.println("Method 7: " + s9);
        System.out.println();

        // Method 8
        String s10 = new String(s_buffer);
        System.out.println("Method 8: " + s10);
        System.out.println();

        // Method 9
        String s11 = s_builder.toString();
        System.out.println("Method 9: " + s11);
        System.out.println();
    }
}

Output

Method 1: Geeks

Method 2: Geeks

Method 2 Alternative: Geeks

Method 3: eek

Method 4: eek

Method 4 Alternative: eeks

Method 5: Geeks

Method 6: eek

Method 7: eek

Method 8: Geeks

Method 9: Geeks...

String Methods in Java

String Methods	Description
int length()	Returns the number of characters in the String.
Char charAt(int i)	Returns the character at ith index.
String substring (int i)	Return the substring from the ith index character to end.
String substring (int i, int j)	Returns the substring from i to j-1 index.
String concat( String str)	Concatenates specified string to the end of this string.
int indexOf (String s)	Returns the index within the string of the first occurrence of the specified string. If String s is not present in input string then -1 is returned as the default value.
int indexOf (String s, int i)	Returns the index within the string of the first occurrence of the specified string, starting at the specified index.
Int lastIndexOf( String s)	Returns the index within the string of the last occurrence of the specified string. If String s is not present in input string then -1 is returned as the default value.
boolean equals( Object otherObj)	Compares this string to the specified object.
boolean equalsIgnoreCase (String anotherString)	Compares string to another string, ignoring case considerations.
int compareTo( String anotherString)	Compares two string lexicographically.
int compareToIgnoreCase( String anotherString)	Compares two string lexicographically, ignoring case considerations. Note: In this case, it will not consider case of a letter (it will ignore whether it is uppercase or lowercase).
String toLowerCase()	Converts all the characters in the String to lower case.
String toUpperCase()	Converts all the characters in the String to upper case.
String trim()	Returns the copy of the String, by removing whitespaces at both ends. It does not affect whitespaces in the middle.
String replace (char oldChar, char newChar)	Returns new string by replacing all occurrences of oldChar with newChar. Note: s1 is still feeksforfeeks and s2 is geeksgorgeeks
boolean contains(CharSequence sequence)	Returns true if string contains contains the given string.
Char[] toCharArray():	Converts this String to a new character array.
boolean startsWith(String prefix)	Return true if string starts with this prefix.

Example of String Constructor and String Methods

Below is the implementation of string constructors and methods in Java.

Java

// Java program to illustrate different 
// constructors and methods in String class
import java.io.*;
import java.util.*;

class Geeks
{
    public static void main (String[] args)
    {
        String s= "GeeksforGeeks";
        // or String s= new String ("GeeksforGeeks");

        // Returns the number of characters in the String
        System.out.println("String length = " + s.length());

        // Returns the character at ith index
        System.out.println("Character at 3rd position = "
                           + s.charAt(3));

        // Return the substring from the ith  index character
        // to end of string
        System.out.println("Substring " + s.substring(3));

        // Returns the substring from i to j-1 index
        System.out.println("Substring  = " + s.substring(2,5));

        // Concatenates string2 to the end of string1
        String s1 = "Geeks";
        String s2 = "forGeeks";
        System.out.println("Concatenated string  = " +
                            s1.concat(s2));

        // Returns the index within the string
        // of the first occurrence of the specified string
        String s4 = "Learn Share Learn";
        System.out.println("Index of Share " +
                           s4.indexOf("Share"));

        // Returns the index within the string of the
        // first occurrence of the specified string,
        // starting at the specified index
        System.out.println("Index of a  = " +
                           s4.indexOf('a',3));

        // Checking equality of Strings
        Boolean out = "Geeks".equals("geeks");
        System.out.println("Checking Equality  " + out);
        out = "Geeks".equals("Geeks");
        System.out.println("Checking Equality  " + out);

        out = "Geeks".equalsIgnoreCase("gEeks ");
        System.out.println("Checking Equality " + out);

        // If ASCII difference is zero then 
        // the two strings are similar
        int out1 = s1.compareTo(s2);
        System.out.println("the difference between ASCII value is="+out1);
        
        // Converting cases
        String w1 = "GeeKyMe";
        System.out.println("Changing to lower Case " +
                            w1.toLowerCase());

        // Converting cases
        String w2 = "GeekyME";
        System.out.println("Changing to UPPER Case " +
                            w2.toUpperCase());

        // Trimming the word
        String w4 = " Learn Share Learn ";
        System.out.println("Trim the word " + w4.trim());

        // Replacing characters
        String str1 = "feeksforfeeks";
        System.out.println("Original String " + str1);
        String str2 = "feeksforfeeks".replace('f' ,'g') ;
        System.out.println("Replaced f with g -> " + str2);
    }
}

Output:

For Set -2, you can refer: Java.lang.String class in Java | Set 2

StringBuffer Class in Java

Rahul Agrawal

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Article Tags :

Practice Tags :

String Class in Java

Creating a String

1. Using String literal

2. Using new keyword

Example of Creating String in Java

String Constructors in Java

String(byte[] byte_arr)

String(byte[] byte_arr, Charset char_set)

String(byte[] byte_arr, int start_index, int length)

String(byte[] byte_arr, int start_index, int length, Charset char_set)

String(char[] char_arr)

String(char[] char_array, int start_index, int count)

String(int[] uni_code_points, int offset, int count)

String(StringBuffer s_buffer)

String(StringBuilder s_builder)

Example String Constructor in Java

String Methods in Java

Example of String Constructor and String Methods

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