Java varargs 要求不定数量的变量

Question

我正在尝试应用可变参数。我已经声明了一个需要无限数量变量的方法，如下所示:

private Subject carMonitor;

public AdvancedMonitor(Subject ... carMonitors){
    for (Subject carMonitor : carMonitors){
    this.carMonitor = carMonitor;
    carMonitor.registerObserver(this);
    }
}

但是，当我尝试在主方法中调用它时，除了一个参数之外我无法使用任何其他参数:

    BigCar bigCar = new BigCar();
    SmallCar smallCar = new SmallCar();
    AdvancedMonitor doubleAdvancedDisplay1 = new AdvancedMonitor();
    AdvancedMonitor doubleAdvancedDisplay2 = new AdvancedMonitor(bigCar);
    AdvancedMonitor doubleAdvancedDisplay3 = new AdvancedMonitor(bigCar, smallCar);

只有第二个有效。这是为什么？

与我的界面有关吗？

public interface Subject {
    public void registerObserver(Observer o);
    public void removeObserver(Observer o);
    public void notifyObservers();
}

大型汽车界面 - 小型汽车目前几乎相同:

public class BigCar implements Subject {
    private ArrayList observers;
    private int state;

    public BigCar(){
        observers = new ArrayList();
    }

    public void registerObserver(Observer o){
        observers.add(o);
    }

    public void removeObserver(Observer o){
        int i = observers.indexOf(o);
        if (i >= 0){
            observers.remove(i);
        }
    }

    public void notifyObservers(){
        for (int i = 0; i < observers.size(); i++){
            Observer observer = (Observer)observers.get(i);
            observer.update(state);
        }
    }

    public void stateChanged() {
        notifyObservers();
    }

    public void setState(int state){
        this.state = state;
        stateChanged();
    }
}

Answer 1

我写了以下代码:

public class Test {
    public static class AdvancedMonitor {
        private String carMonitor;

        public AdvancedMonitor(String... carMonitors) {
            for (String carMonitor : carMonitors) {
                this.carMonitor = carMonitor;
                System.out.println(this.carMonitor);
            }
        }
    }

    public static void main(String[] args) {
        String bigCar = "bigCar";
        String smallCar = "smallCar";
        System.out.println("step 1");
        AdvancedMonitor doubleAdvancedDisplay1 = new AdvancedMonitor();
        System.out.println();
        System.out.println("step 2");
        AdvancedMonitor doubleAdvancedDisplay2 = new AdvancedMonitor(bigCar);
        System.out.println();
        System.out.println("step 3");
        AdvancedMonitor doubleAdvancedDisplay3 = new AdvancedMonitor(bigCar, smallCar);
    }
}

我有以下结果:

step 1

step 2
bigCar

step 3
bigCar
smallCar

在我看来，都正确。你的情况有什么问题吗？您使用 logging 或 System.out.println 来调试您的问题吗？看来您的问题不在于 Java varagrs，但在 carMonitor.registerObserver(this) 中出现了一些异常。

P.S. 另外，您知道每个 AdvancedMonitor 都只有一个变量 carMonitor 吗？并使用 new AdvancedMonitor(bigCar,smallCar); 结果你只有在 private String carMonitor; 中使用smallCar的AdvancedMonitor？

P.P.S. 在 construstor 中使用 this 也是个坏主意，因为运行 contrustor 时并没有真正创建对象。