Java Generic code example

Java Generic code example

A piece of code is worth thousands of thousand

Package Com.apkkids.javalanguage;import Java.util.arraylist;import Java.util.List;/** * @author WXB * Java Generic example */ Public  class generictest {    //generic interface     Public  interface mycollection<T>{         PublicT get (int position); PublicT Add (t T); }//generic interface inheritance     Public  interface MyList<t> extends mycollection<t> {}//Generic class     Public Static  class Mylistimpl<t> implements MyList<t >{         PublicT get (int position) {System.out.println ("Get value at position"+ position);return NULL; } PublicT Add (T t) {SYSTEM.OUT.PRINTLN ("Add"+t.tostring ());return NULL; }    }//A set of classes to be used     Public Static  class Fruit{} Public Static  class Apple extends Fruit{} Public Static  class Strawberry extends Fruit{} Public Static  class fujiapple extends Apple{}/** * @param args * *     Public Staticvoid Main (string[] args) {//Instantiate generic classMylist<string> strlist =NewMylistimpl<string> (); Strlist.add ("Test"); Strlist.get (0);The following code shows that:list<apple> is not a subclass of list<fruit>, and in more general words, the generic type has no relation to whether it is a subtype. //list<apple> apples = new arraylist<apple> ();//list<fruit> fruits = apples;        //Use the extends wildcard,list<apple> and list<strawberry> objects can be assigned to LIST<? extends fruit>        List<Apple> apples =NewArraylist<apple> ();List<Strawberry> Strawberrys =NewArraylist<strawberry> ();List<?Extends fruit> fruits = apples; Fruits = Strawberrys;//Use the? Super Wildcard,list<fruit> object can be assigned to LIST<? Super Apple>        List<Fruit> fruits2 =NewArraylist<fruit> ();List<?Super apple> apples2 = fruits2;//Summary of the characteristics of the extends and the super wildcard, we can draw the following conclusions://1. If you want to get data from a data type, use the? Extends wildcard characterFruits.get (0);//The following three lines will compile the error//Fruits.add (New Apple ());//Fruits.add (New Strawberry ());//Fruits.add (New Fruit ()); //2. If you want to write an object into a data structure, use the? Super wildcard characterApples2.add (NewApple ()); Apples2.add (NewFujiapple ()); Object o = Apples2.get (0);only OBEJCT objects are available when//removed//3. If you want to save and take it, do not use wildcard characters. }}

Java Generic code example