如何修复 pmd 违规“NullAssignment"? [英] How to fix pmd violation "NullAssignment"?

问题描述

PMD 报告 NullAssignment 以下代码，修复它的最佳做法是什么?

PMD report NullAssignment of the following code, what is the best practice to fix it?

将对象分配为 null 是一种代码异味.考虑重构.

Assigning an Object to null is a code smell. Consider refactoring.

以下代码不是我写的，我也有疑问，为什么创建一个临时的定时器实例，然后将这个实例分配给定时器?startTimer 和 stopTimer 将在多线程上下文中使用.

The following code is not written by me, I also have a question on why creating a temporary timer instance, then assign this instance to timer? startTimer and stopTimer will be used in multithread context.

private Timer timer;

private void startTimer() {
    if (timer == null) {
        Timer aTimer = timerService.createTimer(DEFAULT_TIMER_VALUE, null);
        aTimer.setListener(this);
        timer = aTimer;
    }
}

private void stopTimer() {
    if (timer != null) {
        Timer aTimer = timer;
        timer = null;
        aTimer.cancel();
        aTimer.setListener(null);
    }
}

public void start() {
  synchronized(..) {
     startTimer();
  }
}

public void stop() {
  synchronized(..) {
     stopTimer();
  }
}

推荐答案

这段代码是在错误的情况下编写的，相信设置为 null 的引用会被垃圾回收更快.

This code is written in the false believe that a reference that is set to null is garbage collected faster.

因此来自 PMD 的消息是这个错误的信念是被编码的.

Therefore the message from PMD is that this false believe was coded.

这是一个错误的假设，因为垃圾收集器在内存耗尽时运行，它收集所有没有引用的对象.

This is a wrong assumption as the garbage collector runs when the memory is exhausted and it collects all objects that have no reference left on them.

即使调用 System.gc() 也不会导致垃圾收集器运行.该调用只是对垃圾收集器的一个提示，但当垃圾收集器确定有足够的可用内存时，它将不会运行.

Even calling System.gc() will not cause the garbage collector to run. The call is merely a hint to the garbage collector but when the garbage collector detemines that enough free memory is avaible it will not run.

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