java---- wrapper class

java wrapper class

 1. Make the object class accessible to the world, including simple type attributes and values:

        Object o=12;   // error

        Object o=new Integer(12);

        class Integer{

             int value;

             public Integer(int value){

                  this.value=value;

         }

}

   8 wrapper classes: int ===" Integer

                      char ===》 Character

          The other six are all capitalized

                      double  ===》 Double

                      。。。。

           All eight are in the lang package

 2. Function: Provide object form for 8 simple types, let Object unify all data;

                 For properties of numeric type, distinguish between 0 and null;

 3, the conversion between the simple type string of the wrapper class

       1）int <----> Integer

            int i==12;

            Integer ii=new Integer(i);

            int i2=ii.intValue();

        2) int <------> String

            String s=i+" "; 

            int i3=Integer.parseInt(s);  // call static method with obvious class name

        3） Integer <-------> String

               String s2=ii.toString();

               Integer ii2=Integer.valueOf(s2);

 3, jdk 5.0 automatic sealing

      Conversion between simple types and wrapper classes is done automatically by the compiler.