phantomref.html

来自「java类库详细讲解」· HTML 代码 · 共 108 行

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<TITLE>Determining When an Object Will Be Reclaimed
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  <h3>
    e108.  
    Determining When an Object Will Be Reclaimed</h3>

A phantom reference is used to determine when an object is just about
to be reclaimed. Phantom references are safer to use than finalization
because once an object is phantom reachable, it cannot be resurrected.


<pre>
    // Create the phantom reference.
    ReferenceQueue rq = new ReferenceQueue();
    PhantomReference pr = new PhantomReference(<font color="#0066ff"><i>object</i></font>, rq);
    
    // Wait until the object is about to be reclaimed.
    try {
        while (true) {
            Reference r = rq.remove();
            if (r == pr) {
                // The object is about to be reclaimed.
                // Clear the referent so that it can be reclaimed.
                r.clear();
            }
        }
    } catch (InterruptedException e) {
    }
</pre>
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            &nbsp;Related Examples
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e106. <a class="eglink" href="SoftRef.html?l=rel">
    Holding onto an Object Until Memory Becomes Low
</a>
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e107. <a class="eglink" href="WeakRef.html?l=rel">
    Determining When an Object Is No Longer Used
</a>
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