java - ""的正确用法

Question

我不熟悉“泛型”。是否正确使用“<T extends SuperClass>”？您是否同意使用泛型后的代码更好？

Before using Generics
=================================================

public abstract class SuperSample {

    public void getSomething(boolean isProcessA) {
        doProcessX();
        if(isProcessA){
            doProcessY(new SubASample());
        }else{
            doProcessY(new SubBSample());
        }
    }

    protected abstract void doProcessX();

    protected void doProcessY(SubASample subASample) {
        // Nothing to do
    }

    protected void doProcessY(SubBSample subBSample) {
        // Nothing to do
    }

}

public class SubASample extends SuperSample {

    @Override
    protected void doProcessX() {
        System.out.println("doProcessX in SubASample");
    }

    @Override
    protected void doProcessY(SubASample subASample) {
        System.out.println("doProcessY in SubASample");
    }

}

public class Sample {

    public static void main(String[] args) {
        SubASample subASample = new SubASample();
        subASample.getSomething(true);
    }

}

After using Generics
=================================================

public abstract class SuperSample {

    public void getSomething(boolean isProcessA) {
        doProcessX();
        if(isProcessA){
            doProcessY(new SubASample());
        }else{
            doProcessY(new SubBSample());
        }
    }

    protected abstract void doProcessX();

    protected abstract <T extends SuperSample> void doProcessY(T subSample);

}

public class SubASample extends SuperSample {

    @Override
    protected void doProcessX() {
        System.out.println("doProcessX in SubASample");
    }

    @Override
    protected <T extends SuperSample> void doProcessY(T subSample) {
        System.out.println("doProcessY in SubASample");
    }

}

public class Sample {

    public static void main(String[] args) {
        SubASample subASample = new SubASample();
        subASample.getSomething(true);
    }

}

Answer 1

如果您想做我认为您想做的事，我认为这不是正确的方法 (*)。如果你希望每个子类都需要实现一个方法来处理它自己的类型，那么你可以使用 CRTP技巧:

abstract class Super<S extends Super<S>> {
   abstract void process(S s);
}

class SubA extends Super<SubA> {
   void process(SubA s){ /* do something */ }
}

class SubB extends Super<SubB> {
   void process(SubB s){ /* do something */ }
}

请注意，此模式强制执行子类的通用签名，例如class SubA extends Super<SubB>不会编译。

Java 本身在 java.lang.Enum 中使用了这个技巧, 顺便说一下。

(*)如果这不是您要强制执行的行为，请说明。