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.

Practice

1.

What is type casting in Java?

easy

A. Writing a loop

B. Creating a new variable

C. Declaring a method

D. Changing a value from one data type to another

Solution

1. Step 1: Understand the meaning of type casting

   Type casting means converting a value from one data type to another, like from int to double or vice versa.

2. Step 2: Identify the correct description

   Among the options, only changing a value's data type matches the definition of type casting.

3. Final Answer:

   Changing a value from one data type to another -> Option D

4. Quick Check:

   Type casting = Changing data type [OK]

Hint: Type casting means changing data types [OK]

Common Mistakes:

• Confusing type casting with variable declaration
• Thinking type casting creates new variables
• Mixing type casting with control structures

2.

Which of the following is the correct syntax for explicit type casting from double to int in Java?

easy

A. int x = (int) 3.14;

B. int x = int(3.14);

C. int x = 3.14 as int;

D. int x = cast int 3.14;

Solution

1. Step 1: Recall Java explicit casting syntax

   In Java, explicit casting uses parentheses with the target type before the value, like (int) value.

2. Step 2: Match syntax with options

   Only int x = (int) 3.14; uses the correct syntax: int x = (int) 3.14;. Others are invalid in Java.

3. Final Answer:

   int x = (int) 3.14; -> Option A

4. Quick Check:

   Explicit cast uses (type) value [OK]

Hint: Use (type) before value for explicit cast [OK]

Common Mistakes:

• Using function-like cast syntax (e.g., int(3.14))
• Using 'as' keyword which Java doesn't support
• Writing 'cast' keyword which is invalid

3.

What is the output of the following Java code?

double d = 9.99;
int i = (int) d;
System.out.println(i);

medium

A. 9.99

B. 10

C. 9

D. Compilation error

Solution

1. Step 1: Understand explicit cast from double to int

   Casting a double to int truncates the decimal part, it does not round.

2. Step 2: Apply casting to value 9.99

   When casting 9.99 to int, the decimal .99 is dropped, resulting in 9.

3. Final Answer:

   9 -> Option C

4. Quick Check:

   Double to int cast truncates decimals = 9 [OK]

Hint: Casting double to int drops decimals, no rounding [OK]

Common Mistakes:

• Assuming casting rounds the number
• Expecting compilation error due to cast
• Confusing output with original double value

4.

Identify the error in the following Java code snippet:

byte b = 130;

medium

A. Type mismatch: possible lossy conversion from int to byte

B. No error, code runs fine

C. Syntax error: missing cast operator

D. Runtime exception: value too large

Solution

1. Step 1: Understand byte range in Java

   Byte type can hold values from -128 to 127 only.

2. Step 2: Check assigned value 130

   130 is outside byte range, so Java reports a compile-time error about possible lossy conversion.

3. Final Answer:

   Type mismatch: possible lossy conversion from int to byte -> Option A

4. Quick Check:

   Byte range exceeded causes compile error [OK]

Hint: Byte values must be between -128 and 127 [OK]

Common Mistakes:

• Thinking code runs without error
• Expecting runtime exception instead of compile error
• Missing need for explicit cast

5.

Given the code below, what will be the output?

int a = 300;
byte b = (byte) a;
System.out.println(b);

Note: byte range is -128 to 127.

hard

A. 44

B. -56

C. 300

D. Compilation error

Solution

1. Step 1: Understand casting int 300 to byte

   When casting int to byte, Java keeps only the lowest 8 bits of the int value.

2. Step 2: Calculate byte value from 300

   300 in binary is 00000001 00101100 (16 bits). The lowest 8 bits are 00101100 (decimal 44).

3. Step 3: Confirm signed byte value

   300 mod 256 = 44. However, since byte is signed, the value wraps around to -56.

4. Final Answer:

   -56 -> Option B

5. Quick Check:

   Int to byte cast wraps around signed byte range = -56 [OK]

Hint: Casting int to byte keeps lowest 8 bits and wraps signed range [OK]

Common Mistakes:

• Assuming output is original int value
• Confusing signed byte range with unsigned
• Expecting compilation error without cast