Wrapper Classes

A Wrapper class in Java is a class whose object wraps or contains primitive data types. When we create an object to a wrapper class, it contains a field and in this field, we can store primitive data types. In other words, we can wrap a primitive value into a wrapper class object. 

Need of Wrapper Classes

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There are certain needs for using the Wrapper class in Java as mentioned below:

• They convert primitive data types into objects. Objects are needed if we wish to modify the arguments passed into a method (because primitive types are passed by value).
• The classes in java.util package handles only objects and hence wrapper classes help in this case also.
• Data structures in the Collection framework, such as ArrayList and Vector, store only objects (reference types) and not primitive types.
• An object is needed to support synchronization in multithreading.

Advantages of Wrapper Classes

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• Collections allowed only object data.
• On object data we can call multiple methods compareTo(), equals(), toString()
• Cloning process only objects
• Object data allowed null values.
• Serialization can allow only object data.

Below are given examples of wrapper classes in Java with their corresponding Primitive data types in Java.

Primitive Data Types and their Corresponding Wrapper Class

Autoboxing and Unboxing

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1. Autoboxing:

The automatic conversion of primitive types to the object of their corresponding wrapper classes is known as autoboxing. For example – conversion of int to Integer, long to Long, double to Double, etc.

Example:

// Java program to demonstrate Autoboxing
import java.util.ArrayList;

class Autoboxing {
	public static void main(String[] args) {
		char ch = 'a';

		// Autoboxing- primitive to Character object conversion
		Character character = ch;
		System.out.println(character);

		ArrayList<Integer> arrayList = new ArrayList<Integer>();

		// Autoboxing because ArrayList stores only objects
		arrayList.add(25);

		// printing the values from object
		System.out.println(arrayList.get(0));
	}
}

Output:

a
25

2. Unboxing:

It is just the reverse process of autoboxing. Automatically converting an object of a wrapper class to its corresponding primitive type is known as unboxing. For example – conversion of Integer to int, Long to long, Double to double, etc. 

Example:

// Java program to demonstrate Unboxing
import java.util.ArrayList;

class Unboxing {
	public static void main(String[] args) {
		Character ch = 'a';

		// Unboxing - Character object to primitive conversion
		char a = ch;
		
		// printing the value from primitive data type
		System.out.println(a);

		ArrayList<Integer> arrayList = new ArrayList<Integer>();
		arrayList.add(24);

		// Unboxing because get method returns an Integer object
		int num = arrayList.get(0);

		// printing the value from primitive data type
		System.out.println(num);
	}
}

Output:

a
24

Java Wrapper Classes Example:

class WrapperClasses {
	public static void main(String[] args) {
		// byte data type
		byte a = 1;

		// wrapping around Byte object
		Byte byteobj = new Byte(a);

		// int data type
		int b = 10;

		// wrapping around Integer object
		Integer intobj = new Integer(b);

		// float data type
		float c = 18.6f;

		// wrapping around Float object
		Float floatobj = new Float(c);

		// double data type
		double d = 250.5;

		// Wrapping around Double object
		Double doubleobj = new Double(d);

		// char data type
		char e = 'a';

		// wrapping around Character object
		Character charobj = e;

		// printing the values from objects
		System.out.println("Values of Wrapper objects (printing as objects)");
		System.out.println("\nByte object byteobj: " + byteobj);
		System.out.println("\nInteger object intobj: " + intobj);
		System.out.println("\nFloat object floatobj: " + floatobj);
		System.out.println("\nDouble object doubleobj: " + doubleobj);
		System.out.println("\nCharacter object charobj: " + charobj);

		// objects to data types (retrieving data types from objects) unwrapping objects to primitive data types
		byte bv = byteobj;
		int iv = intobj;
		float fv = floatobj;
		double dv = doubleobj;
		char cv = charobj;

		// printing the values from data types
		System.out.println("\nUnwrapped values (printing as data types)");
		System.out.println("\nbyte value, bv: " + bv);
		System.out.println("\nint value, iv: " + iv);
		System.out.println("\nfloat value, fv: " + fv);
		System.out.println("\ndouble value, dv: " + dv);
		System.out.println("\nchar value, cv: " + cv);
	}
}

Output:

Values of Wrapper objects (printing as objects)

Byte object byteobj: 1

Integer object intobj: 10

Float object floatobj: 18.6

Double object doubleobj: 250.5

Character object charobj: a

Unwrapped values (printing as data types)

byte value, bv: 1

int value, iv: 10

float value, fv: 18.6

double value, dv: 250.5

char value, cv: a