是否有可能查看垃圾收集器将删除哪些对象？我不需要对象的内容，但对象的类是必需的。
我尝试编写一个实时应用程序，它创建和删除大量对象，一段时间后应用程序变慢。目前我不确定这是我的代码问题还是外部库的问题。如此完美的输出将标识所有已删除的类以及它们的“计数”（已删除了多少对象）。
我希望有人可以帮助我。
最好， 迈克尔
【问题讨论】：
您可以尝试使用 VisualVM 监控您的应用程序。有一个插件可以提供有关垃圾收集器活动的信息。
【讨论】：
如何为您的对象覆盖finalize 方法并在那里记录类的名称？但请注意，这可能会阻止对象被垃圾收集。
你的班级可能看起来像这样：
public class MyObject {
@Override
public void finalize() throws Throwable {
logger.debug("Object of class {} being garbage collected", this.getClass().getName());
}
}
这是Object.finalize() 方法签名和文档。
/**
* Called by the garbage collector on an object when garbage collection
* determines that there are no more references to the object.
* A subclass overrides the <code>finalize</code> method to dispose of
* system resources or to perform other cleanup.
* <p>
* The general contract of <tt>finalize</tt> is that it is invoked
* if and when the Java<font size="-2"><sup>TM</sup></font> virtual
* machine has determined that there is no longer any
* means by which this object can be accessed by any thread that has
* not yet died, except as a result of an action taken by the
* finalization of some other object or class which is ready to be
* finalized. The <tt>finalize</tt> method may take any action, including
* making this object available again to other threads; the usual purpose
* of <tt>finalize</tt>, however, is to perform cleanup actions before
* the object is irrevocably discarded. For example, the finalize method
* for an object that represents an input/output connection might perform
* explicit I/O transactions to break the connection before the object is
* permanently discarded.
* <p>
* The <tt>finalize</tt> method of class <tt>Object</tt> performs no
* special action; it simply returns normally. Subclasses of
* <tt>Object</tt> may override this definition.
* <p>
* The Java programming language does not guarantee which thread will
* invoke the <tt>finalize</tt> method for any given object. It is
* guaranteed, however, that the thread that invokes finalize will not
* be holding any user-visible synchronization locks when finalize is
* invoked. If an uncaught exception is thrown by the finalize method,
* the exception is ignored and finalization of that object terminates.
* <p>
* After the <tt>finalize</tt> method has been invoked for an object, no
* further action is taken until the Java virtual machine has again
* determined that there is no longer any means by which this object can
* be accessed by any thread that has not yet died, including possible
* actions by other objects or classes which are ready to be finalized,
* at which point the object may be discarded.
* <p>
* The <tt>finalize</tt> method is never invoked more than once by a Java
* virtual machine for any given object.
* <p>
* Any exception thrown by the <code>finalize</code> method causes
* the finalization of this object to be halted, but is otherwise
* ignored.
*
* @throws Throwable the <code>Exception</code> raised by this method
*/
protected void finalize() throws Throwable { }
【讨论】：
不是垃圾回收的对象难道不是更有趣吗？
Anway，像VisualVM 这样的内存分析器是您真正需要的。它可以准确地显示您的应用程序中存在每个类的对象数量，还可以通过比较 GC 前后的堆转储来识别垃圾收集的类和对象县。
【讨论】：
我建议您使用任何 java 分析器，如 JProfiler、Yourkit 等。 很容易看到垃圾回收的对象数量以及对象的类型。
【讨论】：
垃圾回收线程以低优先级运行。所以这个线程没有轮到它来做清理任务。
也不能保证垃圾收集线程会一直运行。在您的应用程序中，垃圾收集的低优先级线程没有机会在应用程序线程上执行。因此堆不会从未使用的对象中清除，因此由于堆大小有限，应用程序会变慢。
您可以通过覆盖public void finalize() 方法来计算垃圾收集的对象数量。更多详情请查看javadoc
我建议您使用一些 java 分析器来诊断内存问题。
【讨论】：