Java Arrays and Strings Practice

Practise Java arrays, 2D arrays, String methods, StringBuilder and wrapper classes on everyday tasks.

Beginner8 problemsUpdated October 23, 2026

Review first: Arrays, 2D Arrays, Strings, StringBuilder, Wrapper Classes and Autoboxing

1.Marks statistics

Beginner

Given int[] marks = {56, 91, 78, 34, 88};, print the total, the average and the highest mark.

Show hint

Loop once, adding to a total and tracking the highest so far. Cast before dividing for the average.

Show solution

Java

public class Main {
    public static void main(String[] args) {
        int[] marks = {56, 91, 78, 34, 88};
        int total = 0;
        int highest = marks[0];
        for (int m : marks) {
            total += m;
            if (m > highest) highest = m;
        }
        System.out.println("Total: " + total);
        System.out.println("Average: " + (double) total / marks.length);
        System.out.println("Highest: " + highest);
    }
}

Output

Total: 347
Average: 69.4
Highest: 91

2.Sort and search an array

Beginner

Sort int[] nums = {42, 7, 19, 3, 25};, print it with Arrays.toString, and find the index of 19 with Arrays.binarySearch.

Show hint

binarySearch only works on a sorted array.

Show solution

Java

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] nums = {42, 7, 19, 3, 25};
        Arrays.sort(nums);
        System.out.println(Arrays.toString(nums));
        System.out.println(Arrays.binarySearch(nums, 19));
    }
}

Output

[3, 7, 19, 25, 42]
2

3.Row and column totals

Beginner

For the grid {{3, 1, 4}, {1, 5, 9}, {2, 6, 5}}, print each row's total on one line, then each column's total on the next.

Show hint

For column totals, put the column loop on the outside.

Show solution

Java

public class Main {
    public static void main(String[] args) {
        int[][] grid = {{3, 1, 4}, {1, 5, 9}, {2, 6, 5}};

        StringBuilder rows = new StringBuilder();
        for (int[] row : grid) {
            int sum = 0;
            for (int v : row) sum += v;
            rows.append(sum).append(' ');
        }
        System.out.println(rows.toString().trim());

        StringBuilder cols = new StringBuilder();
        for (int c = 0; c < grid[0].length; c++) {
            int sum = 0;
            for (int[] row : grid) sum += row[c];
            cols.append(sum).append(' ');
        }
        System.out.println(cols.toString().trim());
    }
}

Output

8 15 13
6 12 18

4.Count the vowels

Beginner

Count the vowels (either case) in "Programming In Java Is Fun".

Show hint

Lower-case the text, loop over toCharArray(), and check "aeiou".indexOf(c) >= 0.

Show solution

Java

public class Main {
    public static void main(String[] args) {
        String text = "Programming In Java Is Fun";
        int count = 0;
        for (char c : text.toLowerCase().toCharArray()) {
            if ("aeiou".indexOf(c) >= 0) count++;
        }
        System.out.println(count);
    }
}

Output

5.Palindrome check

Beginner

Write static boolean isPalindrome(String s) that ignores spaces and case, and test it with "Never odd or even" and "Java".

Show hint

Clean the string, then compare it with new StringBuilder(cleaned).reverse().toString() using equals.

Show solution

Java

public class Main {
    static boolean isPalindrome(String s) {
        String cleaned = s.replace(" ", "").toLowerCase();
        return cleaned.equals(new StringBuilder(cleaned).reverse().toString());
    }

    public static void main(String[] args) {
        System.out.println(isPalindrome("Never odd or even"));
        System.out.println(isPalindrome("Java"));
    }
}

Output

true
false

6.Split an email address

Beginner

Split "asha.rao@example.com" into the user part and the domain, and print the domain in upper case.

Show hint

indexOf('@') finds the split point; substring extracts each part.

Show solution

Java

public class Main {
    public static void main(String[] args) {
        String email = "asha.rao@example.com";
        int at = email.indexOf('@');
        String user = email.substring(0, at);
        String domain = email.substring(at + 1);
        System.out.println(user);
        System.out.println(domain.toUpperCase());
    }
}

Output

asha.rao
EXAMPLE.COM

7.Build a string efficiently

Beginner

Use a StringBuilder to build "1, 2, 3, 4, 5, 6, 7, 8, 9, 10" and print it with its length.

Show hint

Append a separator before every number except the first.

Show solution

Java

public class Main {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        for (int i = 1; i <= 10; i++) {
            if (i > 1) sb.append(", ");
            sb.append(i);
        }
        System.out.println(sb);
        System.out.println(sb.length());
    }
}

Output

1, 2, 3, 4, 5, 6, 7, 8, 9, 10
29

8.Comparing Integer objects

Beginner

Box 1000 into two Integer variables and compare them with == and with equals. Then do the same with 100. Explain the results.

Show hint

Integer caches values from -128 to 127.

Show solution

Java

public class Main {
    public static void main(String[] args) {
        Integer a = 1000;
        Integer b = 1000;
        Integer c = 100;
        Integer d = 100;
        System.out.println((a == b) + " " + a.equals(b));
        System.out.println((c == d) + " " + c.equals(d));
    }
}

Output

false true
true true

== compares references. Small values come from the Integer cache, so c and d are the same object; 1000 is boxed into two different objects. Always use equals to compare wrapper values.

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