String is Palindrome or not in Java 8 Stream API

March 15, 2026

Hi All,

Today I have released new video on "Java Interview Coding Question | String is Palindrome or not in Java 8 Stream API"

This is frequently asked question in Java Interview.

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package org.practice.basicprgms;

import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

public class PalindromeString {

	public static void main(String[] args) {
		String input = "madam";
		String revStr = "";
		// 1. Using StringBuilder reverse() inside Stream
		
			boolean result =
					Stream.of(input)
							.map(str -> new StringBuilder(str).reverse().toString())
							.anyMatch(rev -> rev.equals(input));
			System.out.println("Using StringBuilder reverse(): String is Palindrome? : "+ result);
			

		// 2. Using reduce() (Very Popular Interview Method)
			revStr = input.chars()
							.mapToObj(c -> String.valueOf((char)c))
							.reduce("", (a,b) -> b + a);
			
			System.out.println("Using reduce() : String is Palindrome? :" + revStr.equals(input));
			

		// 3. Using IntStream.range() and allMatch() method
			result = IntStream.range(0, input.length())
							.allMatch(i -> input.charAt(i) == input.charAt(input.length() - 1 -i));
			
			System.out.println("IntStream.range() and allMatch() : String is Palindrome? :" + result);

		// 4. Using IntStream.range() and noneMatch() method
			result = IntStream.range(0, input.length())
								.noneMatch(i -> input.charAt(i) != input.charAt(input.length() - i -1));
			
			System.out.println("Using IntStream.range() and noneMatch() : String is Palindrome? :" + result);
						
		// 5. Using StringBuilder in Stream reduce() method
			revStr = input.chars()
							.mapToObj(c -> (char) c)
							.reduce(
									 new StringBuilder(),
									 (sb, c) -> sb.insert(0, (char)c),
									 StringBuilder::append									
									).toString();
							
			System.out.println("StringBuilder in Stream reduce() : String is Palindrome? :" + revStr.equals(input));
			
		// 6. Using Stream.iterate() method madam
			revStr = IntStream.iterate(input.length()-1, i -> i - 1)
								.limit(input.length())
								.mapToObj(i -> String.valueOf(input.charAt(i)))
								.collect(Collectors.joining());
			
			System.out.println("Using Stream.iterate() method  : String is Palindrome? :" + revStr.equals(input));

		// 7. Using IntStream.range() and joining() to build reverse
			revStr = IntStream.range(0, input.length())
							.mapToObj(i -> input.charAt(input.length() - i -1))
							.map(String::valueOf)
							.collect(Collectors.joining());
			
			System.out.println(" Using IntStream.range() and joining()  : String is Palindrome? :" + revStr.equals(input));

	}

}

output: 
Using StringBuilder reverse(): String is Palindrome? : true
Using reduce() : String is Palindrome? :true
IntStream.range() and allMatch() : String is Palindrome? :true
Using IntStream.range() and noneMatch() : String is Palindrome? :true
StringBuilder in Stream reduce() : String is Palindrome? :true
Using Stream.iterate() method  : String is Palindrome? :true
Using IntStream.range() and joining()  : String is Palindrome? :true