Type casting in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of implicit and explicit casting

What is the output of the following Java code?

Java

public class Main {
    public static void main(String[] args) {
        int a = 130;
        byte b = (byte) a;
        System.out.println(b);
    }
}

A 130

B 0

C -126

D Compilation error

💡 Hint

Remember that byte can only hold values from -128 to 127, so casting int to byte may cause overflow.

The int value 130 is cast to byte. Since byte ranges from -128 to 127, 130 overflows and wraps around to -126.

❓ Predict Output

intermediate

Casting double to int and output

What is the output of this Java code snippet?

Java

public class Main {
    public static void main(String[] args) {
        double d = 9.99;
        int i = (int) d;
        System.out.println(i);
    }
}

A 9

B Compilation error

C 9.99

D 10

💡 Hint

Casting from double to int truncates the decimal part.

Casting double 9.99 to int removes the decimal part, resulting in 9.

❓ Predict Output

advanced

Output of casting with arithmetic expressions

What is the output of this Java program?

Java

public class Main {
    public static void main(String[] args) {
        byte b1 = 40;
        byte b2 = 50;
        byte b3 = (byte) (b1 + b2);
        System.out.println(b3);
    }
}

A 100

B -116

C Compilation error

D 90

💡 Hint

Arithmetic operations on bytes are promoted to int, so explicit cast is needed.

b1 + b2 is promoted to int 90, then cast back to byte 90, which fits in byte range.

❓ Predict Output

advanced

Casting objects and ClassCastException

What happens when you run this Java code?

Java

public class Main {
    public static void main(String[] args) {
        Object obj = "Hello";
        Integer num = (Integer) obj;
        System.out.println(num);
    }
}

A ClassCastException at runtime

B null

C Compilation error

D Hello

💡 Hint

Casting an object to an incompatible type causes runtime error.

The object holds a String, but is cast to Integer, causing ClassCastException at runtime.

🧠 Conceptual

expert

Number of elements after casting and filtering

Consider this Java code snippet. How many elements are in the resulting array after casting and filtering?

Java

import java.util.Arrays;
import java.util.stream.IntStream;

public class Main {
    public static void main(String[] args) {
        Object[] arr = {1, 2.5, 3, 4.0f, 5L, "6", 7};
        int[] result = Arrays.stream(arr)
            .filter(o -> o instanceof Number)
            .mapToInt(o -> ((Number) o).intValue())
            .filter(i -> i > 3)
            .toArray();
        System.out.println(result.length);
    }
}

A 4

B 3

C 5

D 6

💡 Hint

Count only elements that are Number instances and have intValue() > 3.

Numbers are 1,2.5,3,4.0f,5L,7 ("6" is String). Their int values: 1,2,3,4,5,7. Filter >3 gives 4,5,7 → 3 elements.