泛型参数

public class Animal { private String id; private String name; public String getId() { return id; } public void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } }

 

public class Cat extends Animal implements Comparable<Cat>{ public int compareTo(Cat arg0) { return this.getId().compareTo(arg0.getId()); } }

 

public class Dog extends Animal implements Comparable<Dog> { public int compareTo(Dog arg0) { return this.getId().compareTo(arg0.getId()); } }

 

public class demo<E> { List rsList=new ArrayList(); public E getById(E o) { System.out.println(o); return o ; } }

 

public class Demo1 { public <E extends Animal>void getByid(List<E> e) { } public void getByidL(List<Animal> list) { } }

 

public class DemoTest { public static void main(String[] args) { System.out.println("***********"); demo<String> demo=new demo<String>(); demo.getById("ddddd"); } public void test() { List<Dog> list=new ArrayList<Dog>(); List<Animal>list1=new ArrayList<Animal>(); Demo1 demo=new Demo1(); demo.getByidL(list1);//只能是Animal demo.getByid(list);//可以使Animal或它的继承类或实现类 demo.getByid(list1); // demo.getByidL(list);//this is wrong because List<Dog> is not List<Animal> } /** * 创建内部类来依据name来排序 * @author wei * */ class NameCompare implements Comparator<Cat> { public int compare(Cat arg0, Cat arg1) { return arg0.getName().compareTo(arg1.getName()); } } /** * 创建的内部类来依据id来排序 * @author wei * */ class IdCompare implements Comparator<Cat> { public int compare(Cat arg0, Cat arg1) { return arg0.getId().compareTo(arg1.getId()); } } public void test1() { List<Cat>rslist=new ArrayList<Cat>(); NameCompare nameCompare=new NameCompare(); Collections.sort(rslist, nameCompare);//调用了 } }