弱引用与设置为 Null

Question

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

例如，在下面的代码中，变量 "test" 是对 "testString" 的强引用。当我将 "test" 设置为 null 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 有什么意义呢？

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 
  }
}

我为什么要使用 WeakReference？

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

在你的例子中，这两种情况没有区别。但是，请考虑以下与您的示例类似的示例，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 
  }
}

AND

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 
  }
}

弱引用与设置为 Null

Weak Reference vs setting to Null

java

weak-references