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Demo<? super A> a = new Demo<C>();
a.setT(new B());//a.setT(new C())报错;
B b = (B)a.getT();
System.out.println(b);
class A extends C{
public String toString(){
return "aaaaaaaaaaa";
}
}
class B extends A{
public String toString(){
return "bbbbbbbbb";
}
}
class C {
public String toString(){
return "cccccccccccc";
}
}
class Demo<T >{
private T t;
public Demo(){
t= null;
}
public Demo(T t){
this.t = t;
}
public T getT() {
return t;
}
public void setT(T t) {
this.t = t;
}
}