Java Wrapper Classes

What are Wrapper Classes?

• Definition: Wrapper classes in Java are used to convert primitive data types into objects. Each primitive type has a corresponding wrapper class.
• Purpose: These classes are essential when treating primitive types as objects, particularly in collections that only accept objects.

List of Wrapper Classes

• Boolean: wraps a boolean primitive.
• Character: wraps a char primitive.
• Byte: wraps a byte primitive.
• Short: wraps a short primitive.
• Integer: wraps an int primitive.
• Long: wraps a long primitive.
• Float: wraps a float primitive.
• Double: wraps a double primitive.

Key Concepts

• Autoboxing: The automatic conversion of a primitive type to its corresponding wrapper class.
  Example: int num = 10; Integer obj = num; (Here, num is automatically converted to Integer).
• Unboxing: The reverse process, where a wrapper class is converted back to its corresponding primitive type.
  Example: Integer obj = new Integer(10); int num = obj; (Here, obj is converted back to int).

Why Use Wrapper Classes?

• Collections: Wrapper classes are necessary when using the Java Collections Framework (like ArrayList, HashMap, etc.) since these collections can only store objects, not primitives.
• Utility Methods: Wrapper classes provide useful utility methods for type conversion, value comparison, and handling null values.

Example Code

import java.util.ArrayList;

public class WrapperExample {
    public static void main(String[] args) {
        // Using ArrayList with wrapper class
        ArrayList<Integer> numbers = new ArrayList<>();
        numbers.add(10); // Autoboxing
        numbers.add(20);

        // Accessing elements (Unboxing)
        int firstNumber = numbers.get(0);
        System.out.println("First number: " + firstNumber);
    }
}

Conclusion

Wrapper classes are vital in Java for managing primitive data types as objects, facilitating the use of collections, and offering additional functionalities. A solid understanding of autoboxing and unboxing is essential for effective utilization of these classes.