Java泛型的应用

一、泛型类

 package generics;
 /**
  * 泛型类，格式：public class 类名<泛型类型1, ...>
  * @author zhongfg
  * @date 2015-06-16
  * @param <T>
  */
 class Student<T> {

     private T num;

     public T getNum() {
         return num;
     }

     public void setNum(T num) {
         this.num = num;
     }

 }

 public class GenericsClass {
     public static void main(String[] args) {

         Student<String> s1 = new Student<String>();
         s1.setNum("001");
         String num1 = s1.getNum();
         System.out.println(num1);

         System.out.println("----------------");

         Student<Integer> s2 = new Student<Integer>();
         s2.setNum(2);
         int num2 = s2.getNum();
         System.out.println(num2);
     }
 }

二、泛型方法

 package generics;
 /**
  * 泛型方法，public <泛型类型> 返回值  方法名(泛型类型)
  * @author zhongfg
  * @date 2015-06-16
  */
 class Actor {

     public <T> void show(T t){

         System.out.println(t);
     }

 }

 public class GenericsMethod {

     public static void main(String[] args) {

         Actor a = new Actor();
         a.show("Angelababy");
         a.show(26);
     }
 }

三、泛型接口

 package generics;
 /**
  * 泛型类，格式：public interface 接口名<泛型类型1, ...>
  * @author zhongfg
  * @date 2015-06-16
  * @param <T>
  */
 interface Person<T> {

     public abstract void show(T t);
 }

 class PersonImpl<T> implements Person<T> {

     @Override
     public void show(T t) {
         // TODO Auto-generated method stub
         System.out.println(t);
     }
 }

 public class GenericsInterface {
     public static void main(String[] args) {

         Person<String> p1 = new PersonImpl<String>();
         p1.show("黄晓明");

         Person<Integer> p2 = new PersonImpl<Integer>();
         p2.show(38);
     }
 }

四、泛型高级之通配符

 package generics;

 import java.util.ArrayList;
 import java.util.Collection;

 /**
  * 泛型高级（通配符）
  * ？：任意类型，如果没有明确指定，那么就是Object或者任意的Java类了
  * ？ extends E：向下限定，E及其子类
  * ? super E：向上限定，E及其父类
  * @author zhongfg
  * @date 2015-06-16
  */
 class Animal {

 }

 class Dog extends Animal {

 }

 class Cat extends Animal {

 }

 public class GenericsWildcard {
     public static void main(String[] args) {

         //明确指明泛型的时候，前后必须一致
         Collection<Object> c1 = new ArrayList<Object>();
 //        Collection<Object> c2 = new ArrayList<Animal>(); 报错，前后类型不一致
 //        Collection<Object> c3 = new ArrayList<Dog>(); 同上
 //        Collection<Object> c4 = new ArrayList<Cat>(); 同上

         //?表示任意类型都是可以的
         Collection<?> c5 = new ArrayList<Object>();
         Collection<?> c6 = new ArrayList<Animal>();
         Collection<?> c7 = new ArrayList<Dog>();
         Collection<?> c8 = new ArrayList<Cat>();

         //？ extends E：向下限定，E及其子类
 //        Collection<? extends Animal> c9 = new ArrayList<Object>(); 报错，Object不是Animal子类
         Collection<? extends Animal> c10 = new ArrayList<Animal>();
         Collection<? extends Animal> c11 = new ArrayList<Dog>();
         Collection<? extends Animal> c12 = new ArrayList<Cat>();

         //? super E：向上限定，E及其父类
         Collection<? super Animal> c13 = new ArrayList<Object>();
         Collection<? super Animal> c14 = new ArrayList<Animal>();
 //        Collection<? super Animal> c15 = new ArrayList<Dog>(); 报错，Dog不是Animal及其以上的类型
 //        Collection<? super Animal> c16 = new ArrayList<Cat>(); 同上
     }
 }