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| <h1 class="title topictitle1" id="ariaid-title1">Reachability</h1> |
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| <div class="body conbody"> |
| <p class="p"> Objects in a heap dump have references to other objects. These can either be |
| via field references (for simple objects), array elements (for object arrays) |
| or via various hidden references. For instance every object contains a reference to |
| its type, and each class contain a reference to the class loader which loaded |
| the class.</p> |
| |
| <p class="p">These objects and references form a directed graph. The objects are the nodes, |
| the references are the directed links between the nodes. The |
| garbage collection roots are the roots of this graph. |
| </p> |
| |
| <dl class="dl"> |
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| <dt class="dt dlterm">Reachable</dt> |
| <dd class="dd">An object is reachable from another object if there is a |
| path following the directed links from the source object to the destination object. |
| </dd> |
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| <dt class="dt dlterm">Unreachable object</dt> |
| <dd class="dd">If there is no path from a garbage collection root |
| to an object then it is unreachable. There is then no way a legitimate Java program |
| can every get access to this object, so it is safe for the Java virtual machine to |
| discard this object from the heap. This process of determining unreachable objects and |
| discarding them, thus making room for more objects to be allocated as required, is |
| called garbage collection. |
| </dd> |
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| </dl> |
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| <div class="related-links"> |
| <div class="linklist relinfo relconcepts" xml:lang="en-us" lang="en-us"><strong>Related concepts</strong><br /> |
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| <li class="linklist"><a class="link" href="gcroots.html">Garbage collection roots</a></li></ul></div> |
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