Simplifying the use of wrapper class objects

  • The official syntax to create a wrapper class Integer object is: 

      Integer i1 = new Integer(99);

  • In contrast, creating an int primitive typed variable is much simpler: 

     int i1 = 99;

  • To simplify the use of wrapper class objects, the Java provides a simplified syntax: 

      Integer i1 = 99 ;  // Same as:   Integer i1 = new Integer(99)

    This goes for every wrapper class !!

Autoboxing

  • The Java compiler has the following special mechanism/rule built in: 

      When assigning a primitive value x to  a wrapper class object:

        WrapperClass var  =   x 

  the Java compiler will replace  x  with:

        WrapperClass var  =  new WrapperClass( x )

    Example: 

            Integer i2 =  99 ;

  ===>  Integer i2 = new Integer( 99 )

  • This automatic replacement mechanism is called autoboxing

  • Boxing = converting a primitive value to its wrapper object

Autoboxing   example

  • Example using the simplified syntax to create wrapper objects: 

        public static void main(String[] args)
    {
        Integer i1 = new Integer(99);  // Official syntax
        System.out.println( i1 );
        
        Integer i2 =  99 ;             //  ≡  new Integer(99)
        System.out.println( i2 );

        Double d1 = new Double(88.0);  // Official syntax
        System.out.println( d1 );
        
        Double d2 =  88.0 ;            //  ≡  new Double(88.0)
        System.out.println( d2 );
    }

  • Autoboxing is a built-in service provided by the Java compiler (to make using wrapper object more convenient)

DEMO: demo/12-wrapper/02-simplified/AutoBoxing.java

Another simplifying rule for wrapper class objects

  • The official syntax to use the value stored in a wrapper class Integer object is: 

      Integer o = new Integer(99);  // Integer object
  int x = 1;                    // Primitive integer

  x = x + o.intValue(); // Must use accessor method (private)

    Writing the official syntax is very tedious

  • To simplify the use of wrapper class objects, the Java provides a simplified syntax: 

      x = x + o ; // Same as:   x = x + o.intValue()

    This goes for every wrapper class !!

Auto-unboxing

  • The Java compiler has another special mechanism/rule built in: 

      When using a wrapper object  o in an expression (= computation)
  the Java compiler will replace:
 
         o  ===>   o.accessorMethod()

    Example: 

      Integer o = new Integer(99);  // Integer object
  int x = 1;                    // Primitive integer

  x = x +  o ;     ===>     x = x +  o.intValue() ;

  • This automatic replacement mechanism is called auto-unboxing

  • Unboxing = converting a wrapper object to a primitive value

Auto-unboxing   example

  • Example using the simplified syntax to use the value stored in wrapper objects: 

     public static void main(String[] args)
 {
    Integer i1 = new Integer(99); 
        
    int x;
 
    x = 4 + i1.intValue(); // Official syntax
    x = 5 + i1;            // Auto-Unboxing
 }

  • Auto-unboxing is a built-in service provided by the Java compiler (to make using wrapper object more convenient)

DEMO: demo/12-wrapper/02-simplified/AutoUnboxing.java