泛型中类型参数中的常量

Question

我正在阅读 Thinking in java 4th edition，我遇到了这段代码

class SuperHero<POWER extends SuperPower> {
    POWER power;

    SuperHero(POWER power) {
        this.power = power;
    }

    POWER getPower() {
        return power;
    }
}

我查看了这段代码的整个类定义，但似乎找不到关键字 POWER，所以我假设它是一个常量？在这种情况下，“POWER”实际上是什么？

这是整个类的定义

package tij4.generics;

//: generics/EpicBattle.java
//Demonstrating bounds in Java generics.
import java.util.*;

//Marker Interface
interface SuperPower {
}

interface XRayVision extends SuperPower {
    void seeThroughWalls();
}

interface SuperHearing extends SuperPower {
    void hearSubtleNoises();
}

interface SuperSmell extends SuperPower {
    void trackBySmell();
}

class SuperHero<POWER extends SuperPower> {
    POWER power;

    SuperHero(POWER power) {
        this.power = power;
    }

    POWER getPower() {
        return power;
    }
}

class SuperSleuth<POWER extends XRayVision> extends SuperHero<POWER> {
    SuperSleuth(POWER power) {
        super(power);
    }

    void see() {
        power.seeThroughWalls();
    }
}

class CanineHero<POWER extends SuperHearing & SuperSmell> extends
        SuperHero<POWER> {
    CanineHero(POWER power) {
        super(power);
    }

    void hear() {
        power.hearSubtleNoises();
    }

    void smell() {
        power.trackBySmell();
    }
}

class SuperHearSmell implements SuperHearing, SuperSmell {
    public void hearSubtleNoises() {
    }

    public void trackBySmell() {
    }
}

class DogBoy extends CanineHero<SuperHearSmell> {
    DogBoy() {
        super(new SuperHearSmell());
    }
}

public class EpicBattle {
    // Bounds in generic methods:
    static <POWER extends SuperHearing> void useSuperHearing(
            SuperHero<POWER> hero) {
        hero.getPower().hearSubtleNoises();
    }

    static <POWER extends SuperHearing & SuperSmell> void superFind(
            SuperHero<POWER> hero) {
        hero.getPower().hearSubtleNoises();
        hero.getPower().trackBySmell();
    }

    public static void main(String[] args) {
        DogBoy dogBoy = new DogBoy();
        useSuperHearing(dogBoy);
        superFind(dogBoy);
        // You can do this:
        List<? extends SuperHearing> audioBoys;
        // But you can't do this:
        // List<? extends SuperHearing & SuperSmell> dogBoys;
    }
} // /:~

添加信息： 我还查看了这个包中包含的不同类。他们都没有定义枚举“POWER”

Answer 1

它只是一个泛型类型名称，就像java.util.List<T> 中的T。作者只是为这种类型选择了一个较大的名称。