Wrapper class in Java

Everything in Java is an object. To make this statement true, Java introduces wrapper classes for each of its primitive data types. Wrapper classes are used to convert the primitive data type into an object.

Autoboxing is a feature of Java that automatically converts primitive data type into an object of the corresponding wrapper class. Unboxing is just opposite of autoboxing. This feature converts wrapper class object into the corresponding primitive data type.

Java provides eight wrapper classes. All the wrapper classes accept Boolean, and Character are subclasses of Number class, whereas Boolean and Character directly extend the Object class.

Conversion of Primitive data type into Wrapper class object

There are three ways by which we can achieve this-

1. Simply by assigning a primitive value to a wrapper class variable. Example- Interger i = 10;
2. By passing the corresponding primitive value to a wrapper class constructor. Example- Byte b = new Byte(8);
3. By invoking static method valueOf() of the wrapper class. Example- Double d = Double.valueOf(30);

Note- You can even pass String as an argument to any wrapper class constructor except Character. The Character class constructor only takes char as an argument.

Example- from Primitive to Wrapper

public class PrimitiveToWrapper
{
	public static void main(String args[])
	{
		int i = 45;
		Integer j = i; // this is autoboxing
		Integer k = new Integer(i); // calling constructor
		Integer l = Integer.valueOf(i); // convert int to Integer
		System.out.println("j = "+j);
		System.out.println("k = "+k);
		System.out.println("l = "+l);
	}
}	

Output

j = 50
k = 50
l = 50

Conversion of Wrapper class object into Primitive data type

The primitive value stored in wrapper class object can be retrieved using a method of the format primitiveValue() where primitive points the name of primitive data type.

Example- from Wrapper to Primitive

public class WrapperToPrimitive
{
	public static void main(String args[])
	{
		Integer i = new Integer(50); //converting int to Integer
		int j = i.intValue(); //obtaining int from Integer
		int k = i; //this is unboxing
		System.out.println("i = "+i);
		System.out.println("j = "+j);
		System.out.println("k = "+k);
	}
}

Output

i = 50
j = 50
k = 50