How to Reverse a String in Java

  1. Reverse a String Using the reverse() Method in Java
  2. Reverse a String Using Custom Code in Java
  3. Reverse a String Using the append() Method in Java
  4. Reverse a String Using Recursion in Java
  5. Reverse a String Using Stack in Java

This tutorial introduces how to reverse a string in Java and lists some example codes to understand it.

There are several ways to reverse a string, like reverse(), sorted(), and parallelSort() methods, etc. Let’s see the examples.

Reverse a String Using the reverse() Method in Java

In this example, we use the reverse() method of the StringBuilder class to get the string in reverse order, and we use the toString() method to get string object from the StringBuilder object. See the example below.

public class SimpleTesting {
	public static void main(String[] args) {
		String str = "DelfStack";
		System.out.println(str);
		StringBuilder strb = new StringBuilder(str);
		str = strb.reverse().toString();
		System.out.println(str);
	}
}

Output:

DelfStack
kcatSfleD

Reverse a String Using Custom Code in Java

If you don’t want to use built-in methods, then use a custom code that will swap the string characters using a loop and collect them into a char array that further converted into a string. See the example below.

public class SimpleTesting {
	public static void main(String[] args) {
		String str = "DelfStack";
		System.out.println(str);
		char[] ch = str.toCharArray();
	    int begin = 0;
	    int end = ch.length-1;
	    char temp;
	    while(end>begin){
	        temp = ch[begin];
	        ch[begin] = ch[end];
	        ch[end] = temp;
	        end--;
	        begin++;
	    }
	    str = new String(ch);
	    System.out.println(str);
	}
}

Output:

DelfStack
kcatSfleD

Reverse a String Using the append() Method in Java

This is another approach to reverse a string in Java. Here, we use charAt() and append() methods inside the for loop to fetch and store chars into StringBuilder object. See the example below.

public class SimpleTesting {
	public static void main(String[] args) {
		String str = "DelfStack";
		System.out.println(str);
		StringBuilder dest = new StringBuilder();
		for (int i = (str.length() - 1); i >= 0; i--){
			dest.append(str.charAt(i));
		}
		System.out.println(dest);
	}
}

Output:

DelfStac
kcatSfleD

Reverse a String Using Recursion in Java

Recursion is a technique in which a function calls itself again and again till the base condition. We can use recursion to reverse the string, as in the below example.

public class SimpleTesting {
	public static void main(String[] args) {
		String str = "DelfStack";
		System.out.println(str);
		String reverseStr = reverseIt(str, str.length()-1);
		System.out.println(reverseStr);
	}
	static String reverseIt(String str, int index){
		if(index == 0){
			return str.charAt(0) + "";
		}
		char letter = str.charAt(index);
		return letter + reverseIt(str, index-1);
	}
}

Output:

DelfStack
kcatSfleD

Reverse a String Using Stack in Java

We can use the Stack class to reverse the string. We use the push() method of Stack to collect the characters into the stack and then use the pop() method to fetch the stored characters in reverse order. See the example below.

import java.util.Stack;

public class SimpleTesting {
	public static void main(String[] args) {
		String str = "DelfStack";
		System.out.println(str);
		Stack<Character> stack = new Stack<>();
	    for (int i = 0; i < str.length(); i++) {
	        stack.push(str.charAt(i));
	    }
	    StringBuilder strb = new StringBuilder();
	    while (!stack.empty()) {
	        strb.append(stack.pop());
	    }
	    System.out.println(strb);
	}
}

Output:

DelfStack
kcatSfleD

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