Enhanced for loop in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of enhanced for loop with array

What is the output of the following Java code using an enhanced for loop?

Java

public class Main {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3};
        int sum = 0;
        for (int num : numbers) {
            sum += num;
        }
        System.out.println(sum);
    }
}

A Compilation error

B 123

C 0

D 6

💡 Hint

Think about how the enhanced for loop adds each number to sum.

The enhanced for loop iterates over each element in the array 'numbers'. It adds each element to 'sum'. The sum of 1 + 2 + 3 is 6, so the output is 6.

❓ Predict Output

intermediate

Enhanced for loop with a list

What will be printed by this Java code using an enhanced for loop over a List?

Java

import java.util.List;
import java.util.ArrayList;
public class Main {
    public static void main(String[] args) {
        List<String> fruits = new ArrayList<>();
        fruits.add("apple");
        fruits.add("banana");
        fruits.add("cherry");
        for (String fruit : fruits) {
            System.out.print(fruit.charAt(0));
        }
    }
}

A applebananacherry

B a b c

C abc

D Compilation error

💡 Hint

Look at what character is printed for each fruit.

The enhanced for loop goes through each fruit in the list. For each fruit, it prints the first character (charAt(0)). So it prints 'a' from apple, 'b' from banana, and 'c' from cherry, resulting in 'abc'.

❓ Predict Output

advanced

Enhanced for loop with modification inside loop

What is the output of this Java code that tries to modify array elements inside an enhanced for loop?

Java

public class Main {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3};
        for (int x : arr) {
            x = x * 2;
        }
        for (int x : arr) {
            System.out.print(x + " ");
        }
    }
}

A 1 2 3

B 2 4 6

C Compilation error

D Runtime exception

💡 Hint

Does changing 'x' inside the loop change the original array?

The enhanced for loop variable 'x' is a copy of each element. Changing 'x' does not change the original array elements. So the array remains {1, 2, 3}, and the second loop prints '1 2 3 '.

❓ Predict Output

advanced

Enhanced for loop with multidimensional array

What will this Java program print when using an enhanced for loop over a 2D array?

Java

public class Main {
    public static void main(String[] args) {
        int[][] matrix = {{1, 2}, {3, 4}};
        int total = 0;
        for (int[] row : matrix) {
            for (int val : row) {
                total += val;
            }
        }
        System.out.println(total);
    }
}

A 10

B Compilation error

C 24

D 0

💡 Hint

Add all numbers in the 2D array.

The outer enhanced for loop iterates over each row (which is an int array). The inner loop iterates over each value in that row. Adding 1 + 2 + 3 + 4 equals 10, so the output is 10.

🧠 Conceptual

expert

Behavior of enhanced for loop with Iterable and Iterator

Which statement about the enhanced for loop in Java is true?

A It requires manual handling of the loop index variable.

B It internally uses an Iterator to loop over elements of Iterable collections.

C It allows modifying the collection elements directly during iteration.

D It can only be used with arrays, not with collections.

💡 Hint

Think about how enhanced for loops work with collections like ArrayList.

The enhanced for loop works with arrays and any class that implements Iterable. Internally, it uses an Iterator to get elements one by one. It does not allow modifying the collection elements directly, and it does not require manual index handling.