Question

I am reading Thinking in java 4th edition and I encountered this code

class SuperHero<POWER extends SuperPower> {
    POWER power;

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

    POWER getPower() {
        return power;
    }
}

I was looking at the whole class definition of this code and I can’t seem to find the keyword POWER, so I am assuming it is a constant? what is “POWER” actually is in this case?

here is the whole class definition

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;
    }
} // /:~

ADDED INFO:
I also looked at the different classes included in this package. and none of them defines an enum “POWER”

Answer 1

It’s just a generic type name, just as T in java.util.List<T>. The author just chose a larger name for this type.