Wrapper Classes in Java

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. Let’s check on the wrapper classes in Java with examples:

Need of Wrapper Classes

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

1. 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).
2. The classes in java.util package handles only objects and hence wrapper classes help in this case also.
3. Data structures in the Collection framework, such as ArrayList and Vector, store only objects (reference types) and not primitive types.
4. An object is needed to support synchronization in multithreading.

Advantages of Wrapper Classes

1. Collections allowed only object data.
2. On object data we can call multiple methods compareTo(), equals(), toString()
3. Cloning process only objects
4. Object data allowed null values.
5. 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

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

Autoboxing and Unboxing

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

// 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 a = ch;

        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

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

// 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;

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

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

        // printing the values from primitive data types
        System.out.println(num);
    }
}

Output

24

Java Wrapper Classes Example

Java

// Java program to demonstrate Wrapping and UnWrapping
// in Classes
import java.io.*;

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

        // wrapping around Byte object
        Byte byteobj = new Byte(a);
        // Use with Java 9
        // Byte byteobj = Byte.valueOf(a);

        // int data type
        int b = 10;

        // wrapping around Integer object
        Integer intobj = new Integer(b);
        // Use with Java 9
        // Integer intobj = Integer.valueOf(b);

        // float data type
        float c = 18.6f;

        // wrapping around Float object
        Float floatobj = new Float(c);
        // Use with Java 9
        // Float floatobj = Float.valueOf(c);

        // double data type
        double d = 250.5;

        // Wrapping around Double object
        Double doubleobj = new Double(d);
        // Use with Java 9
        // Double doubleobj = Double.valueOf(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

Custom Wrapper Classes in Java

Java Wrapper classes wrap the primitive data types. We can create a class that wraps data inside it. So let us check how to create our own custom wrapper class in Java. It can be implemented for creating certain structures like queues, stacks, etc.

Example:

Java

// Java Program to implement
// Custom wrapper class
import java.io.*;

// wrapper class
class Maximum {
    private int maxi = 0;
    private int size = 0;

    public void insert(int x)
    {
        this.size++;
        if (x <= this.maxi)
            return;
        this.maxi = x;
    }

    public int top() { return this.maxi; }

    public int elementNumber() { return this.size; }
};

//
class GFG {
    public static void main(String[] args)
    {
        Maximum x = new Maximum();
        x.insert(12);
        x.insert(3);
        x.insert(23);

        System.out.println("Maximum element: " + x.top());
        System.out.println("Number of elements inserted: "
                           + x.elementNumber());
    }
}

Output

Maximum element: 23
Number of elements inserted: 3

FAQs in Wrapper Class

1. Which are the wrapper classes in Java?

A Wrapper class in Java is a class whose object wraps or contains primitive data types.

2. Why use the wrapper class in Java?

The wrapper class in Java is used to convert primitive data types into objects. Objects are needed if we wish to modify the arguments passed into a method.

3. What are the 8 wrapper classes in Java?

There are 8 Wrapper classes in Java these are Boolean, Byte, Short, Character, Integer, Long, Float, Double.