Wrapper Classes

Java is an object-oriented programming language, which means everything should theoretically be an object. However, for performance reasons, Java provides eight primitive data types (int, char, double, boolean, etc.) that are not objects.

A Wrapper class in Java provides the mechanism to convert these primitive data types into object equivalents. These wrapper classes are part of the java.lang package.

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The Eight Wrapper Classes

Here is the mapping of primitive types to their corresponding Wrapper classes:

Primitive Type	Wrapper Class
boolean	Boolean
char	Character
byte	Byte
short	Short
int	Integer
long	Long
float	Float
double	Double

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Why Do We Need Wrapper Classes?

1. Collections Framework: Java's Collection framework (like ArrayList, HashMap, HashSet) strictly works with Objects. You cannot store primitive types like int inside an ArrayList. You must use the Integer wrapper class.
2. Utility Methods: Wrapper classes provide helpful constants (like Integer.MAX_VALUE) and utility methods (like Integer.parseInt(String)) to manipulate primitive data.
3. Synchronization: Multithreading synchronization requires an object lock. Primitives cannot be used for locks.

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Autoboxing and Unboxing

Before Java 5, developers had to manually convert primitives to wrapper objects and vice-versa. Java 5 introduced Autoboxing and Unboxing to make this process automatic and seamless.

1. Autoboxing

The automatic conversion of a primitive data type into its corresponding Wrapper class object by the Java compiler is known as Autoboxing.

public class LabWrapper1 {

  public static void main(String args[]) {
    int primitiveInt = 50;

    // Manual boxing (Prior to Java 5)
    Integer obj1 = Integer.valueOf(primitiveInt);

    // Autoboxing (Java 5 and later)
    Integer obj2 = primitiveInt;

    System.out.println("Primitive: " + primitiveInt);
    System.out.println("Autoboxed Object: " + obj2);
  }
}

2. Unboxing

The automatic conversion of a Wrapper class object back into its corresponding primitive data type is known as Unboxing.

public class LabWrapper2 {

  public static void main(String args[]) {
    Integer obj = new Integer(100);

    // Manual unboxing
    int primitive1 = obj.intValue();

    // Unboxing (Automatic)
    int primitive2 = obj;

    System.out.println("Object: " + obj);
    System.out.println("Unboxed Primitive: " + primitive2);
  }
}

[!NOTE] Even though Autoboxing and Unboxing happen automatically, they still consume CPU cycles under the hood. Avoid unnecessary boxing/unboxing in tight loops for high-performance applications!