如何创建泛型子类的实例？获取错误：“绑定不匹配：类型...不是绑定参数...的有效替代。”

Question

public class ChampionsLeague<Team extends Comparable<Team>> extends League<Team>{
...

ChampionsLeague<Team> league = new ChampionsLeague<>();

这不起作用：

“绑定不匹配：类型team不能有效替代类型 的有界参数 ”

Answer 1

在您的代码中，team只是一个占位符（在此上下文中称为类型变量），并且恰好隐藏了类型team，而不是引用它。换言之，该声明相当于：

public class ChampionsLeague<T extends Comparable<T>> extends League<T> {

因此，它实际上只要求一个实现（扩展）carable自身的类（或接口）。所以这个例子：

public class Ball implements Comparable<Ball> {
    @Override
    public int compareTo(Ball o) { return 0; }
}
// or: public interface Ball extends Comparable<Ball> { }

将起作用：

ChampionsLeague<Ball> test = new ChampionsLeague<Ball>();

// ChampionsLeague needs a type Comparable to Team
public class ChampionsLeague<T extends Comparable<Team>> extends League<T> {

// ChampionsLeague needs a subtype of Team
// In this case, you can make Team implement Comparable<Team> in its own decl.
public class ChampionsLeague<T extends Team> extends League<T> {