Type Casting in Java Interview Questions and Answers for 2 years experience

1. What is type casting in Java?

   • Answer: Type casting, also known as type conversion, is the process of converting a variable from one data type to another. Java supports two types: implicit (automatic) and explicit (manual).

2. Explain implicit type casting with an example.

   • Answer: Implicit casting happens automatically when a smaller data type is assigned to a larger data type without any explicit conversion. For example, assigning an `int` to a `double`: double d = 10;. The `int` value 10 is automatically widened to a `double` value 10.0.

3. Explain explicit type casting with an example.

   • Answer: Explicit casting, also known as narrowing conversion, requires manual intervention using casting operators (e.g., `(int)`, `(double)`). It's used when converting a larger data type to a smaller one. This can lead to data loss if the value doesn't fit within the smaller type. Example: int i = (int) 10.5; (10.5 is converted to 10, the fractional part is truncated).

4. What are the potential risks of explicit type casting?

   • Answer: The main risk is data loss. When narrowing, information might be lost (like the fractional part in the previous example). It can also lead to exceptions like `ClassCastException` if you're casting between incompatible object types.

5. What is the difference between widening and narrowing type casting?

   • Answer: Widening casting is the automatic conversion from a smaller data type to a larger one (e.g., `int` to `long`), generally safe. Narrowing casting is the explicit conversion from a larger data type to a smaller one (e.g., `double` to `int`), potentially leading to data loss or exceptions.

6. Can you cast a String to an Integer in Java? How?

   • Answer: You can't directly cast a String to an Integer. You need to use methods like `Integer.parseInt()` or `Integer.valueOf()`. For example: `int num = Integer.parseInt("123");` or `Integer num = Integer.valueOf("123");`.

7. What happens if you try to cast a value outside the range of the target data type?

   • Answer: You'll get unexpected results. For numerical types, the value might wrap around (for example, with `byte` which has a limited range) or be truncated (e.g., losing the fractional part when casting a `double` to an `int`).

8. Explain the concept of upcasting and downcasting in the context of inheritance.

   • Answer: Upcasting is automatically converting a subclass object to its superclass type. It's safe and usually implicit. Downcasting is explicitly converting a superclass object to a subclass type. It requires an explicit cast and can throw a `ClassCastException` if the object isn't actually an instance of the target subclass.

9. What is the `instanceof` operator used for?

   • Answer: The `instanceof` operator checks if an object is an instance of a particular class or interface. It's often used before downcasting to prevent `ClassCastException` exceptions.

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