Java Wrapper Classes
Wrapper classes in Java provide a way to use primitive data types (int, char, etc.) as objects. Each primitive type has a corresponding wrapper class in the java.lang package.
1. List of Wrapper Classes
| Primitive Type | Wrapper Class |
|---|---|
| byte | Byte |
| short | Short |
| int | Integer |
| long | Long |
| float | Float |
| double | Double |
| char | Character |
| boolean | Boolean |
2. Autoboxing and Unboxing
Autoboxing is the automatic conversion of primitive types to their corresponding wrapper classes. Unboxing is the reverse process.
Example:
Integer num = 10; // Autoboxing: int to Integer
int n = num; // Unboxing: Integer to int
3. Usage in Collections
Wrapper classes are necessary when working with collections that require objects, such as ArrayList.
ArrayList<Integer> numbers = new ArrayList<>();
numbers.add(5); // Autoboxing
4. Common Methods
parseXxx(String s)- Parses a string into a primitive type (e.g.,Integer.parseInt("123")).valueOf(String s)- Returns an instance of the wrapper class.xxxValue()- Converts the wrapper object to a primitive type (e.g.,intValue()).
5. Key Takeaways
- Wrapper classes convert primitives into objects.
- Autoboxing and unboxing simplify conversions between primitives and wrappers.
- Useful when working with collections and generics.
- Provide utility methods for parsing and converting values.