何时以及为什么List remove(Object object)返回false

Question

何时以及为什么该方法boolean java.util.List.remove(Object object)返回false？

文件说明

[该方法返回]如果此操作修改了此List,则返回true,否则返回false.

为什么该操作不会在列表上生效？

(注意:我正在使用的列表的实现是ArrayList)

更新: 我尝试删除的对象确实存在于列表中.我将类添加到List(因此参数this)并将this(在同一个类中)传递给remove方法.因此,对象应该存在于List中(或不存在？).

更新: 这是代码.看看这个delay()方法.我试图从中删除相应的类List.

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Object传入的实际上不在列表中,则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Objects 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,请确保覆盖该equals()方法,以及hashCode()(以维护方法之间的一般契约).