Module 2: Wrapper Class

Wrapper Class

• Wrapper classes are used to convert primitive data types into objects.
• The primitive data types are not objects. They are just data types. So, we need wrapper classes to convert primitive data types into objects.
• There are eight wrapper classes available in Java.
  • Byte
  • Short
  • Integer
  • Long
  • Float
  • Double
  • Character
  • Boolean
• The wrapper classes are present in the java.lang package.
• The wrapper classes are immutable.
• AutoBoxing and Unboxing are the two features of wrapper classes.
  • AutoBoxing is the automatic conversion of primitive data types into objects.
  • Unboxing is the automatic conversion of objects into primitive data types.

import java.lang.*;
class Main{
    public static void main(String[] args){
        int a = 10;
        Integer i = Integer.valueOf(a); // converting int into Integer
        Integer j = a; // autoboxing, now compiler will write Integer.valueOf(a) internally
        System.out.println(a + " " + i + " " + j);
    }
    // using autoboxing and auto unboxing
    public static void main(String[] args){
        Integer a = 10;
        a = a + 10; // unboxing, now compiler will write a.intValue() internally
        System.out.println(a);
        int b = 20;
        Integer c = b; // autoboxing, now compiler will write Integer.valueOf(b) internally
        System.out.println(c);
    }
}

Creating Wrapper Objects.

• There are different constructors available in the wrapper classes to create wrapper objects.

Integer i = new Integer(10);
Integer j = new Integer("10");

• There are different methods available in the wrapper classes to perform operations on wrapper objects.

i.intValue(); // returns the value of this Integer as an int
i.byteValue(); // returns the value of this Integer as a byte
i.shortValue(); // returns the value of this Integer as a short
i.longValue(); // returns the value of this Integer as a long

Similarly, there are different methods available in the wrapper classes to perform operations on wrapper objects.

Autoboxing

• Autoboxing is the automatic conversion of primitive data types into objects.
• The Java compiler applies autoboxing when a primitive value is:
  • Passed as a parameter to a method that expects an object of the corresponding wrapper class.
  • Assigned to a variable of the corresponding wrapper class.

import java.lang.Integer;
class Main{
    public static void main(String[] args){
        int a = 20;
        Integer i = Integer.valueOf(a); // converting int into Integer
        Integer j = a; // autoboxing, now compiler will write Integer.valueOf(a) internally
        System.out.println(a + " " + i + " " + j);
    }
}

Wrapper Objects Conversion

• Wrapper class object can be converted into primitive data types using the intValue(), byteValue(), shortValue(), longValue(), floatValue(), doubleValue(), charValue() and booleanValue() methods.
• intValue(), byteValue(), shortValue(), longValue(), floatValue(), doubleValue(), charValue() methods can be used to convert wrapper objects into primitive data types.

import jdk.incubator.foreign.SymbolLookup;

import java.lang.Integer;

class Main {
    public static void main(String[] args) {
        // Converting primitive data types into wrapper objects
        Integer obj1 = Integer.valueOf(234)
        Double obj2 = Double.valueOf(5.62)
        Boolean obj3 = Boolean.valueOf(true);
        // Converting wrapper objects into primitive data types
        int var1 = obj1.intValue();
        double var2 = obj2.doubleValue();
        boolean var3 = obj3.booleanValue();
    }
}