Type Casting in Java Interview Questions and Answers for freshers

1. What is type casting in Java?

   • Answer: Type casting, also known as type conversion, is the process of converting a variable of one data type into another data type. It's essential for handling different data types in Java's strictly-typed system. There are two main types: implicit and explicit.

2. Explain implicit type casting with an example.

   • Answer: Implicit type casting, or widening conversion, happens automatically when a smaller data type is assigned to a larger data type. No explicit code is needed. For example: int x = 10; double y = x; Here, the integer x is automatically converted to a double y without any explicit cast.

3. Explain explicit type casting with an example.

   • Answer: Explicit type casting, or narrowing conversion, requires a manual cast using parentheses. It's necessary when converting a larger data type to a smaller one, potentially leading to data loss. Example: double z = 10.5; int a = (int) z; Here, the double z is explicitly cast to an integer a, truncating the decimal part.

4. What are the possible data loss scenarios in type casting?

   • Answer: Data loss can occur during narrowing conversions. For example, converting a double to an int truncates the fractional part. Converting a larger integer to a smaller integer (like a long to an int) can lead to overflow if the value exceeds the smaller type's range.

5. What happens if you try to cast a String to an int without proper parsing?

   • Answer: You'll get a compile-time error. Direct casting from String to a numeric type like int is not allowed. You need to use methods like Integer.parseInt() or similar to parse the String into an integer first.

6. How do you cast a String to an integer in Java?

   • Answer: Use Integer.parseInt("yourString"). This method attempts to convert the String to an int. It throws a NumberFormatException if the String cannot be parsed.

7. What is the difference between casting and converting?

   • Answer: In Java, the terms are often used interchangeably, especially in the context of primitive data types. However, a subtle difference is that "converting" might encompass broader data transformations (like converting a String to a Date), while "casting" is more specifically about changing the type of a variable.

8. Can you cast an object of a subclass to its superclass?

   • Answer: Yes, this is called upcasting and is generally safe. It's implicitly allowed because a subclass "is-a" superclass. The subclass object will retain its original type, but the reference will be treated as if it's of the superclass type.

9. Can you cast an object of a superclass to its subclass?

   • Answer: Yes, but this is called downcasting and requires an explicit cast. It's potentially unsafe and can lead to a ClassCastException at runtime if the object isn't actually an instance of the subclass.

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