How to reverse a String in Java

12/13/2017

A String can be converted to an Array of characters and the array is inverted looping from the end to the beginning.

Syntax:

StringBuilder toReturn = new StringBuilder();
	
	char[] tab = input.toCharArray();
	for( int i = tab.length-1 ; i >= 0 ; i--){
	    toReturn.append( tab[i] );	
	}
	
	return toReturn.toString();

Example:

This example creates a method called reverse that converts a String to a CharArray. It loops on all the Characters from the last one to the first one and adds it to a StringBuilder. The output is then returned.
This method is called with 2 sample Strings. The first method reverse is called twice with the output of the first call showing that the output is the same as the input.

public class StringReverse {

    public static String reverse(String input){
	StringBuilder sb = new StringBuilder();
	
	char[] tab = input.toCharArray();
	for( int i = tab.length-1 ; i >= 0 ; i--){
	    sb.append( tab[i] );	
	}
	
	return sb.toString();
    }
    
    public static void main(String[] argv) {

	String test = "This is a test";

	// Call reverse 
	String output = reverse( test );
	
	System.out.println( test + " => " + output );
	
	// Same test calling reverse twice
	System.out.println( test + " => " + reverse( test ) + " => " + reverse(reverse( test )) );

	// With Numbers
	test = "0123456789";

	System.out.println( test + " => " + reverse( test ) );

    }

}

The output will be:

This is a test => tset a si sihT
This is a test => tset a si sihT => This is a test
0123456789 => 9876543210

References:

Java String