java - List remove(Object object) 何时以及为何返回 false

Question

boolean java.util.List.remove(Object object) 方法何时以及为何返回 false？

文档说明

[The method returns] true if this List was modified by this operation, false otherwise.

为什么操作对List不生效？

(注意:我正在使用的 List 的实现是 ArrayList)

更新:我要删除的对象确实存在于列表中。我将该类添加到 List(因此参数 this)并将 this(在同一类中)传递给 remove 方法。因此该对象应该存在于列表中(或者不存在？)。

更新:这是代码。看看 delay() 方法。我尝试从 List 中删除相应的类。

public class Timer extends Object {

    private static List<Timer> allTimers;
    private Long startTime;
    private int delayTime;
    private boolean registered;

    String name;

    public Timer(String name) {
        this.name = name;
        this.registered = true;
        allTimers.add(this);
        Log.d("SpaceDroid", "Foo: Created timer: " + name + " Size: " + this.allTimers.size());

    }

    public Timer(String name, int delayTime) {
        this(name);
        this.delayTime = delayTime;

    }

    public void setDelayTime(int delayTime) {
        this.delayTime = delayTime;

    }

    public boolean delay() {
        if(this.startTime == null) {
            this.startTime = System.currentTimeMillis();
        }

        if(startTime + this.delayTime < System.currentTimeMillis()) {
            if(this.registered) {
                Log.d("SpaceDroid", "Foo: Trying to remove timer: " + name);
                if(this.allTimers.remove(this)) {
                    Log.d("SpaceDroid", "Foo: Successfully removed timer: " + name);
                }
                else {
                    Log.d("SpaceDroid", "Foo: Did not remove timer: " + name);
                }

            }
            return true;

        }
        else {
            return false;

        }

    }

    // The same as resume, just renew the startTime

    public void reset() {
        this.startTime = null;
        this.registered = true;
        this.allTimers.add(this);

    }

    public void resume() {
        this.startTime = System.currentTimeMillis();

    }

    public void pause() {
        // Check if timer is still running
        if(!this.delay()) {
            // Calculate new delayTime
            delayTime = (int) ((startTime + this.delayTime) - System.currentTimeMillis());
            Log.d("SpaceDroid", "Foo: New delay time: " + delayTime + " for timer: " + name);

        }


    }

    public static void resumeAllTimers() {
        List<Timer> timers = new ArrayList<Timer>(Timer.allTimers);
        for (Timer timer : timers) {
            timer.resume();
        }

    }

    public static void pauseAllTimers() {
        List<Timer> timers = new ArrayList<Timer>(Timer.allTimers);
        for (Timer timer : timers) {
            timer.pause();
        }

    }

    public static void disposeAllTimers() {
        Timer.allTimers.clear();
        Timer.allTimers = null;

    }

    public static void initializeAllTimers() {
        allTimers = new ArrayList<Timer>();

    }


}

Answer 1

如果传入的 Object 实际上不在列表中，它不会对列表产生任何影响，因此返回 false。

编辑(感谢 Jai):该方法使用特定的 Object 的 equals() 方法来确定它是否包含该对象。因此，如果您有自定义对象，请确保覆盖 equals()方法，还有 hashCode() (维护方法之间的一般契约)。