Java 通配符泛型例子

请看下面的代码，其中会发生错误的代码已经注释掉，并且写明了错误类型

总体来说，泛型通配符就是为了支持多态时父子类，接口扩展类之间的相互转换而生

 

package test;

import java.util.ArrayList;
import java.util.List;

publicclass GenericTester {
publicstaticvoid main(String[] args){
GenericTester genericTester=new GenericTester();
List<TestA> list=new ArrayList<GenericTester.TestA>();
GenericTester.TestA tester=genericTester.new TestA();
list.add(tester);
TryGeneric1(list);
TryGeneric2(list);
// TryGeneric3(list); has compile error
// TryGeneric4(list); has compile error
}
privateinterface ITest{
publicvoid Test();
}
privateclass TestA implements ITest{

@Override
publicvoid Test() {
// TODO Auto-generated method stub
System.out.println("TestA");
}
}
privatestaticvoid TryGeneric1(List<? extends ITest> testList){
for(ITest tester:testList){
tester.Test();
}
}
privatestaticvoid TryGeneric2(List<?> testList){
// for(ITest tester:testList) // cause error
for(Object tester:testList){
((ITest)tester).Test();
}
}
privatestaticvoid TryGeneric3(List<ITest> testList){
for(ITest tester:testList){
((ITest)tester).Test();
}
}
privatestaticvoid TryGeneric4(List<Object> testList){
for(Object tester:testList){
((ITest)tester).Test();
}