Top 12 Java Programs for Interview with Output (2025 Edition)

✅ Java Program – Sort an Array

package Code;

import java.util.Arrays;

public class ArraySort {
    public static void main(String[] args) {
        int arr[] = {111, 22, 3133, 414, 55, 66, 99, 100, 200, 77};
        System.out.println("Original num: " + Arrays.toString(arr));
        Arrays.sort(arr);
        System.out.println("Sorted Array : " + Arrays.toString(arr));
    }
}

💡 Output:
Original num: [111, 22, 3133, 414, 55, 66, 99, 100, 200, 77]
Sorted Array : [22, 55, 66, 77, 99, 100, 111, 200, 414, 3133]

✅ Java Program – Character Count in String

package Code;

import java.util.HashMap;
import java.util.Map;

public class CharacterCount {
    public static void main(String[] args) {
        String str = "patnabiharamnorsaran";
        Map<Character, Integer> charCount = new HashMap<>();
        for (char c : str.toCharArray()) {
            charCount.put(c, charCount.getOrDefault(c, 0) + 1);
        }
        System.out.println(charCount);
    }
}

💡 Output:
{a=6, b=1, h=1, i=1, m=1, n=3, o=1, p=1, r=3, s=1, t=1}

✅ Java Program – Print Unique Words in a Sentence

package Code;

import java.util.Map;
import org.apache.commons.collections4.map.HashedMap;

public class GFG {
    public static void main(String[] args) {
        String str = "masum delhi patna bihar amnour bihar patna raza";
        String words[] = str.split(" ");
        Map<String, Integer> wordCount = new HashedMap<>();
        for (String word : words) {
            wordCount.put(word, wordCount.getOrDefault(word, 0) + 1);
        }
        for (String word : wordCount.keySet()) {
            if (wordCount.get(word) == 1) {
                System.out.println(word + " " + wordCount.get(word));
            }
        }
    }
}

💡 Output:
masum 1
delhi 1
amnour 1
raza 1

✅ Java Program – Non-Repeating and Repeating Characters

package Code;

public class NonRepeatingCharacter {
    public static void main(String[] args) {
        String str = "amnoursaranbihar";
        System.out.print("Non Repeating Character is : ");
        for (char c : str.toCharArray()) {
            if (str.indexOf(c) == str.lastIndexOf(c)) {
                System.out.print(c + " ");
            }
        }
        System.out.print("\nRepeating Character is = ");
        for (char d : str.toCharArray()) {
            if (str.indexOf(d) != str.lastIndexOf(d)) {
                System.out.print(d + " ");
            }
        }
    }
}

💡 Output:
Non Repeating Character is : m o u b
Repeating Character is = a n r s

✅ Java Program – Prime Numbers from 1 to 100

package Code;

public class PrimeChecker {
    public static void main(String[] args) {
        for (int num = 1; num <= 100; num++) {
            System.out.println(num + " is " + (isPrime(num) ? " prime num" : " non prime number"));
        }
    }
    private static boolean isPrime(int num) {
        if (num <= 1)
            return false;
        for (int i = 2; i <= Math.sqrt(num); i++) {
            if (num % i == 0)
                return false;
        }
        return true;
    }
}

💡 Output (partial):
1 is non prime number
2 is prime num
3 is prime num
...
97 is prime num
100 is non prime number

✅ Java Program – Find Second Highest Number

package Code;

public class SecondHighestNumber {
    public static void main(String[] args) {
        int first = Integer.MIN_VALUE;
        int second = Integer.MIN_VALUE;
        int arr[] = {11, 22, 33, 44, 55, 66, 99, 100, 200, 77};
        for (int num : arr) {
            if (num > first) {
                second = first;
                first = num;
            } else if (num > second && num != first) {
                second = num;
            }
        }
        System.out.println(second);
    }
}

💡 Output:
100

✅ Java Program – Print Triangle Pattern

package Code;

public class Tringle {
    public static void main(String[] args) {
        int row = 8;
        for (int i = 1; i <= row; i++) {
            for (int j = 1; j <= row - i; j++) {
                System.out.print(" ");
            }
            for (int k = 1; k <= i; k++) {
                System.out.print("* ");
            }
            System.out.println();
        }
    }
}

💡 Output:
*
* *
* * *
* * * *
* * * * *
* * * * * *
* * * * * * *
* * * * * * * *

✅ Java Program – Count Uppercase Letters

package Code;

public class UpperCaseCountInString {
    public static void main(String[] args) {
        String str = "PatnaDelhiKolkataBiharAmnourSARAn";
        int count = 0;
        System.out.print("Uppercase letters: ");
        for (char c : str.toCharArray()) {
            if (Character.isUpperCase(c)) {
                System.out.print(c + " ");
                count++;
            }
        }
        System.out.println("\nTotal uppercase letters: " + count);
    }
}

💡 Output:
Uppercase letters: P D K B A S A R A
Total uppercase letters: 9

✅ Java Program – Count White Spaces and Words

package Code;

public class WhiteSpaceCount {
    public static void main(String[] args) {
        String str = "hell      aa ad ddsa ddd dd";
        int count = 0;
        for (int i = 0; i <= str.length() - 1; i++) {
            if (str.charAt(i) == ' ') {
                count++;
            }
        }
        System.out.println("Total white space count is : " + count);

        int wordCount = 0;
        for (int j = 0; j <= str.length() - 1; j++) {
            if (str.charAt(j) == ' ' && str.charAt(j + 1) != ' ') {
                wordCount++;
            }
        }
        System.out.println("Total word Count is : " + wordCount);
    }
}

💡 Output:
Total white space count is : 14
Total word Count is : 5

✅ Java Program – Remove Duplicate Words

package Code;

import java.util.HashSet;
import java.util.Set;

public class WordDublicate {
    public static void main(String[] args) {
        String Str = "hello ram delhi patna bihar delhi patna bihar";
        String[] words = Str.split(" ");
        Set<String> uniq = new HashSet<>();
        for (String word : words) {
            uniq.add(word.trim());
        }
        for (String word : uniq) {
            System.out.println(word);
        }
    }
}

💡 Output:
hello
ram
delhi
patna
bihar

✅ Java Program – Expand String

package Code;

public class ExpandString {
public static void main(String[] args) {
String str = "a2b3c4";
String result = "";
    for (int i = 0; i < str.length(); i += 2) {
        char ch = str.charAt(i);
        int count = Character.getNumericValue(str.charAt(i + 1));

        for (int j = 1; j <= count; j++) {
            result = result + ch;
        }
    }
    System.out.println(result);
}

💡 Output:
aabbbcccc

✅ Java Program – String Compression Program 


package program;
import java.util.LinkedHashMap;
import java.util.Map;

public class StringCompressMap {
    public static void main(String[] args) {

        String input = "aaabbbfccc";
        String result = "";
        // LinkedHashMap maintains insertion order
        Map charCountMap = new LinkedHashMap<>();
        // Count frequency of each character
        for (char ch : input.toCharArray()) {
            charCountMap.put(ch, charCountMap.getOrDefault(ch, 0) + 1);
        }
        // Build compressed string
        for (Map.Entry entry : charCountMap.entrySet()) {
            result = result + entry.getKey() + entry.getValue();
        }
        // Print output
        System.out.println(result);
    }
}

💡 Output:
a3br3f1c3

Location: New York, NY, USA

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