Question

这是一个工作的java代码，用于提供一个基本引擎类，它处理各种游戏使用的大量引擎实现的余额监听器注册。例如会有一个演示引擎，它维护演示游戏的演示平衡和相同引擎的现金版本，从后台获取余额等。这里的关键不是实际的java，而是如何实现这种模式在JavaScript中。我尝试了大约30种不同的方法，包括使用John Resigs“简单的JavaScript继承”和“JavaScript：权威指南”中定义的extend（）糖，使用各种模块模式，使用那个=这个等等。为这个问题而努力。

这是工作的java代码：

File Engine.java：

package com.test;
public abstract class Engine {
    BalanceListener externalBalanceListener = null;
    double balance = 0;
    public void registerBalanceListener(BalanceListener balanceListener) {
        externalBalanceListener = balanceListener;
        balanceListener.update(balance);  // call once when first register
    }
    public double getBalance() {
        return balance;
    }
    protected void setBalance(double newBal) {
        if (newBal != balance) {
            balance = newBal;
            if (externalBalanceListener != null) {
                externalBalanceListener.update(newBal);
            }
        }       
    }
    public abstract double startGame(double stake, int numLines);
}

文件BalanceListener.java

package com.test;
public interface BalanceListener {
    void update(double balance);
}

文件DemoEngine.java

package com.test;
import java.util.Random;

public class DemoEngine extends Engine {
    public DemoEngine() {
        setBalance(10000);
    }
    public double startGame(double stake, int numLines) {
        double wonAmount;
        Random random = new Random();

        setBalance (getBalance() - (stake * numLines));

        // some game logic
        wonAmount = Math.round((random.nextDouble() * 10)) * stake;
        setBalance (getBalance() + wonAmount);          
        return wonAmount;
    }
}

文件DemoGame.java

package com.test;

public class DemoGame {

    public class MyListener implements BalanceListener {
        public MyListener(){
        }
        public void update(double balance) {
            System.out.println("new balance: " + balance);
        }
    }

    public static void main(String[] args) {
        Engine engine = new DemoEngine();

        DemoGame demoGame = new DemoGame();

        BalanceListener balanceListener = demoGame.new MyListener();

        engine.registerBalanceListener(balanceListener);

        engine.startGame(10, 20);
    }
}

这是一个简单的（失败的）尝试在JavaScript中使用相同的东西（参见http://jsfiddle.net/fmX67/）

function Engine() {
    this.balance = 0;
    this.externalBalanceListener;

    this.registerBalanceListener = function(l) {
            this.externalBalanceListener= l;
            this.externalBalanceListener(this.balance);
    };

    this.getBalance = function() {
        return this.balance;
    };

    this.setBalance = function (newBal) {
        if (newBal != this.balance) {
            this.balance = newBal;
            if (this.externalBalanceListener != undefined) {
                this.externalBalanceListener(newBal);
            }
        }
    };

};

function DemoEngine() {
    this.startGame = function(stake, numLines) {
        var won;

        setBalance(this.getBalance() - stake*numlines);
        won = Math.round(Math.random() * 10) * Stake;

        this.setBalance(this.getBalance() + won);

        return won;
    };
}

DemoEngine.prototype = Engine;

function DemoGame() {

    function balanceListener(balance) {
        console.log(balance);
    }

    var engine = new DemoEngine();

    engine.registerBalanceListener(balanceListener); // This throws an exception: Uncaught TypeError: Object [object Object] has no method 'registerBalanceListener'

    engine.startGame(10, 25);
}

var game = new DemoGame();

显然我不知道自己在做什么（尽管阅读了几本JS书籍）。我假设我可以使用合成而不是尝试继承，但这限制了语言的使用以及可以实现的模式。

编辑：这是Shaun West的答案的工作版本。见http://jsfiddle.net/fmX67/3/

function Engine() {
    this.balance = 0;
    this.externalBalanceListener;

    this.registerBalanceListener = function(l) {
            this.externalBalanceListener= l;
            this.externalBalanceListener(this.balance);
    };

    this.getBalance = function() {
        return this.balance;
    };

    this.setBalance = function (newBal) {
        if (newBal != this.balance) {
            this.balance = newBal;
            if (this.externalBalanceListener != undefined) {
                this.externalBalanceListener(newBal);
            }
        }
    };

};

function DemoEngine() {
    this.setBalance(1000);
    this.startGame = function(stake, numLines) {
        var won;

        this.setBalance(this.getBalance() - stake*numLines);
        won = Math.round(Math.random() * 10) * stake;

        this.setBalance(this.getBalance() + won);

        return won;
    };
}

DemoEngine.prototype = new Engine();

function DemoGame() {

    function balanceListener(balance) {
        console.log(balance);
    }

    var engine = new DemoEngine();

    engine.registerBalanceListener(balanceListener); // This throws an exception: Uncaught TypeError: Object [object Object] has no method 'registerBalanceListener'

    engine.startGame(10, 25);
}


var game = new DemoGame();

Answer 1

对于来自Java的人来说似乎很奇怪，在你的尝试中你会想要改变这个：

DemoEngine.prototype = Engine;

对此：

DemoEngine.prototype = new Engine();

如果您想了解更多信息，这个答案非常好：What is the 'new' keyword in JavaScript?

如何在JavaScript中实现这个java模式（使用继承）？

1 个答案: