java - 弱引用与设置为 Null

Question

这个问题在这里已经有了答案:





Is there a practical use for weak references? [duplicate]

(9 个回答)


4年前关闭。




使用 Wea​​kReference 和将强引用类型设置为 null 有什么区别？

例如，在以下代码中，变量“test”是对“testString”的强引用。当我将“测试”设置为空时。不再有强引用，因此“testString”现在有资格进行 GC。因此，如果我可以简单地将对象引用“test”设置为等于 null，那么拥有 WeakReference Type 的意义何在？

class CacheTest {
  private String test = "testString";

  public void evictCache(){
    test = null; // there is no longer a Strong reference to "testString" 
    System.gc(); //suggestion to JVM to trigger GC 
  }
}

为什么我要使用 Wea​​kReference ？

class CacheTest {
  private String test = "testString";
  private WeakReference<String> cache = new WeakReference<String>(test);

  public void evictCache(){
    test = null; // there is no longer a Strong reference to "testString" 
    System.gc(); //suggestion to JVM to trigger GC 
  }
}

Answer 1

在您的示例中，这两种情况没有区别。但是，请考虑以下与您类似的示例，其中存在区别:

class CacheTest {
  private String test = "testString";
  private String another = "testString";

  public void evictCache(){
    test = null; // this still doesn't remove "testString" from the string pool because there is another strong reference (another) to it.
    System.gc(); //suggestion to JVM to trigger GC 
  }
}

和

class CacheTest {
  private String test = "testString";
  private WeakReference<String> cache = new WeakReference<String>(test);

  public void evictCache(){
    test = null; // this removes "testString" from the pool because there is no strong reference; there is a weak reference only. 
    System.gc(); //suggestion to JVM to trigger GC 
  }
}