A collection framework for the reinforcement of Java Fundamentals Note 31: Overview and basic use of generic classes for collections

1. Why is there a generic type?

(1) The early object type can receive arbitrary types of objects, but in actual use, there will be type conversion problems, there is also a hidden danger, so Java provides generics to solve this security problem .

2. Use of generic classes:

(1) First define a generic class Objecttool, as follows:

1  Packagecn.itcast_04;2 3 /*4 * Generic class: Define Generics on class5  */6  Public classObjecttool<t> {7     PrivateT obj;8 9      PublicT getobj () {Ten         returnobj; One     } A  -      Public voidsetobj (T obj) { -          This. obj =obj; the     } -}

(2) write a test for a generic class:

1  Packagecn.itcast_04;2 3 /*4 * Testing of generic classes5  */6  Public classObjecttooldemo {7      Public Static voidMain (string[] args) {8         //objecttool ot = new Objecttool ();9         //Ten         //ot.setobj (New String ("Wind Qing")); One         //string s = (string) ot.getobj (); A         //System.out.println ("name is:" + s); -         // -         //ot.setobj (new Integer); the         //integer i = (integer) ot.getobj (); -         //System.out.println ("Age is:" + i); -  -         //ot.setobj (New String ("Brigitte")); +         // //classcastexception -         //Integer II = (integer) ot.getobj (); +         //System.out.println ("name is:" + II); A  atSystem.out.println ("-------------"); -  -objecttool<string> ot =NewObjecttool<string>(); -         //ot.setobj (new Integer);//This is the time to compile . -Ot.setobj (NewString ("Brigitte")); -String s =ot.getobj (); inSystem.out.println ("name is:" +s); -  toObjecttool<integer> Ot2 =NewObjecttool<integer>(); +         //ot2.setobj (New String ("Wind Qing"));//This is the time to compile . -Ot2.setobj (NewInteger (27)); theInteger i =ot2.getobj (); *System.out.println ("Age is:" +i); $     }Panax Notoginseng}

The results of the operation are as follows:

A collection framework for the reinforcement of Java Fundamentals Note 31: Overview and basic use of generic classes for collections