Java program to find the biggest palindrome from the given string.

  package com.demo;

import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

public class PlaindromTest {

	public static void main(String[] args) {

		String str = "my as a aaaaaa mom madam";
		biggestPlainDrom(str);
	}

	private static void biggestPlainDrom(String str) {

		StringBuilder builder = new StringBuilder();
		int size = 0;
		List list = new CopyOnWriteArrayList();

		String[] strArr = str.split(" ");
		
		for (String st : strArr) {

			for (int i = st.length() - 1; i >= 0; i--) {

				builder.append(st.charAt(i));
			}
			if (builder.toString().equals(st)) {
				if (size < st.length()) {

					if (list.size() > 0) {
						list.remove(list.size()-1);
					}
					size = st.length();
					list.add(st);
				}
			}
			builder = new StringBuilder();
		}
		System.out.println(list);
	}
}

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Java program to print the output like- input will be "a4k3b2" and output should be after 'a' 4th character, after 'k' 3rd character and the final output : "aeknbd"

public class StringTest {

    public static void main(String[] args) {

        String str = "a4k3b2";// output aeknbd


        System.out.println(replaceChar(str));;
    }

    private static StringBuilder replaceChar(String str) {

        StringBuilder stB = new StringBuilder();

        char[] c = str.toCharArray();

        for (int i = 0; i < c.length; i++) {
            char cha = c[i];
            
            if(Character.isAlphabetic(c[i])) {
                stB.append(cha);
            }else{
                
                int v = c[i-1];
                char value = c[i];
                char digitChar = (char) (v + (value-48));
                stB.append(digitChar);
            }
        }
        return stB;

    }
}

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