Type casting in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is type casting in Java?

Type casting is converting a variable from one data type to another. It helps when you want to treat data as a different type.

beginner

What is the difference between implicit and explicit type casting?

Implicit casting (widening) happens automatically when converting a smaller type to a bigger type (e.g., int to long). Explicit casting (narrowing) requires you to write the cast manually (e.g., double to int).

beginner

How do you explicitly cast a double to an int in Java?

Use parentheses with the target type before the value: <br> int x = (int) 9.7; <br> This cuts off the decimal part.

intermediate

What happens if you cast a large long value to an int?

If the long value is too big for int, the value wraps around and you get a different number. This is called overflow.

intermediate

Can you cast between unrelated object types in Java?

No. You can only cast between compatible types in the same class hierarchy. Otherwise, you get a ClassCastException at runtime.

Which of these is an example of implicit type casting?

A double to int

B String to int

C int to long

D long to byte

Implicit casting happens when converting smaller types to bigger types automatically, like int to long.

What is the result of casting 9.99 (double) to int?

A Error

B 10

C 9.99

D 9

Casting double to int cuts off the decimal part, so 9.99 becomes 9.

Which cast requires explicit syntax in Java?

A double to int

B float to double

C int to long

D byte to short

Casting from double to int is narrowing and requires explicit cast.

What exception occurs if you cast incompatible object types?

A ClassCastException

B IllegalArgumentException

C ArrayIndexOutOfBoundsException

D NullPointerException

Casting incompatible object types throws ClassCastException at runtime.

What happens if a large long value is cast to int?

A Value remains the same

B Value is truncated to fit int size

C Compilation error

D Value is rounded

Casting large long to int truncates the value and may cause overflow.

Explain the difference between implicit and explicit type casting in Java.

Think about when Java does the conversion for you and when you must tell it to convert.

Describe what happens when you cast a double value to an int in Java.

Focus on how the number changes and what you must write in code.