📄 phantomreference.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN""http://www.w3.org/TR/REC-html40/frameset.dtd"><!--NewPage--><HTML><HEAD><!-- Generated by javadoc on Thu Apr 27 23:35:22 PDT 2000 --><TITLE>Java 2 Platform SE v1.3: Class PhantomReference</TITLE><LINK REL ="stylesheet" TYPE="text/css" HREF="../../../stylesheet.css" TITLE="Style"></HEAD><BODY BGCOLOR="white"><!-- ========== START OF NAVBAR ========== --><A NAME="navbar_top"><!-- --></A><TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0"><TR><TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1"><A NAME="navbar_top_firstrow"><!-- --></A><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3"> <TR ALIGN="center" VALIGN="top"> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-summary.html"><FONT CLASS="NavBarFont1"><B>Package</B></FONT></A> </TD> <TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Class</B></FONT> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="class-use/PhantomReference.html"><FONT CLASS="NavBarFont1"><B>Use</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../index-files/index-1.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD> </TR></TABLE></TD><TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM><b>Java<sup><font size=-2>TM</font></sup> 2 Platform<br>Std. Ed. v1.3</b></EM></TD></TR><TR><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> PREV CLASS <A HREF="../../../java/lang/ref/Reference.html"><B>NEXT CLASS</B></A></FONT></TD><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../../index.html" TARGET="_top"><B>FRAMES</B></A> <A HREF="PhantomReference.html" TARGET="_top"><B>NO FRAMES</B></A></FONT></TD></TR><TR><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2"> SUMMARY: INNER | FIELD | <A HREF="#constructor_summary">CONSTR</A> | <A HREF="#method_summary">METHOD</A></FONT></TD><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">DETAIL: FIELD | <A HREF="#constructor_detail">CONSTR</A> | <A HREF="#method_detail">METHOD</A></FONT></TD></TR></TABLE><!-- =========== END OF NAVBAR =========== --><HR><!-- ======== START OF CLASS DATA ======== --><H2><FONT SIZE="-1">java.lang.ref</FONT><BR>Class PhantomReference</H2><PRE><A HREF="../../../java/lang/Object.html">java.lang.Object</A> | +--<A HREF="../../../java/lang/ref/Reference.html">java.lang.ref.Reference</A> | +--<B>java.lang.ref.PhantomReference</B></PRE><HR><DL><DT>public class <B>PhantomReference</B><DT>extends <A HREF="../../../java/lang/ref/Reference.html">Reference</A></DL><P>Phantom reference objects, which are enqueued after the collector determines that their referents may otherwise be reclaimed. Phantom references are most often used for scheduling pre-mortem cleanup actions in a more flexible way than is possible with the Java finalization mechanism. <p> If the garbage collector determines at a certain point in time that the referent of a phantom reference is <a href="package-summary.html#reachability">phantom reachable</a>, then at that time or at some later time it will enqueue the reference. <p> In order to ensure that a reclaimable object remains so, the referent of a phantom reference may not be retrieved: The <code>get</code> method of a phantom reference always returns <code>null</code>. <p> Unlike soft and weak references, phantom references are not automatically cleared by the garbage collector as they are enqueued. An object that is reachable via phantom references will remain so until all such references are cleared or themselves become unreachable.<P><DL><DT><B>Since: </B><DD>1.2</DD></DL><HR><P><!-- ======== INNER CLASS SUMMARY ======== --><!-- =========== FIELD SUMMARY =========== --><!-- ======== CONSTRUCTOR SUMMARY ======== --><A NAME="constructor_summary"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TD COLSPAN=2><FONT SIZE="+2"><B>Constructor Summary</B></FONT></TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><B><A HREF="../../../java/lang/ref/PhantomReference.html#PhantomReference(java.lang.Object, java.lang.ref.ReferenceQueue)">PhantomReference</A></B>(<A HREF="../../../java/lang/Object.html">Object</A> referent, <A HREF="../../../java/lang/ref/ReferenceQueue.html">ReferenceQueue</A> q)</CODE><BR> Creates a new phantom reference that refers to the given object and is registered with the given queue.</TD></TR></TABLE> <!-- ========== METHOD SUMMARY =========== --><A NAME="method_summary"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TD COLSPAN=2><FONT SIZE="+2"><B>Method Summary</B></FONT></TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> <A HREF="../../../java/lang/Object.html">Object</A></CODE></FONT></TD><TD><CODE><B><A HREF="../../../java/lang/ref/PhantomReference.html#get()">get</A></B>()</CODE><BR> Returns this reference object's referent.</TD></TR></TABLE> <A NAME="methods_inherited_from_class_java.lang.ref.Reference"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor"><TD><B>Methods inherited from class java.lang.ref.<A HREF="../../../java/lang/ref/Reference.html">Reference</A></B></TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><A HREF="../../../java/lang/ref/Reference.html#clear()">clear</A>, <A HREF="../../../java/lang/ref/Reference.html#enqueue()">enqueue</A>, <A HREF="../../../java/lang/ref/Reference.html#isEnqueued()">isEnqueued</A></CODE></TD></TR></TABLE> <A NAME="methods_inherited_from_class_java.lang.Object"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor"><TD><B>Methods inherited from class java.lang.<A HREF="../../../java/lang/Object.html">Object</A></B></TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><A HREF="../../../java/lang/Object.html#clone()">clone</A>, <A HREF="../../../java/lang/Object.html#equals(java.lang.Object)">equals</A>, <A HREF="../../../java/lang/Object.html#finalize()">finalize</A>, <A HREF="../../../java/lang/Object.html#getClass()">getClass</A>, <A HREF="../../../java/lang/Object.html#hashCode()">hashCode</A>, <A HREF="../../../java/lang/Object.html#notify()">notify</A>, <A HREF="../../../java/lang/Object.html#notifyAll()">notifyAll</A>, <A HREF="../../../java/lang/Object.html#toString()">toString</A>, <A HREF="../../../java/lang/Object.html#wait()">wait</A>, <A HREF="../../../java/lang/Object.html#wait(long)">wait</A>, <A HREF="../../../java/lang/Object.html#wait(long, int)">wait</A></CODE></TD></TR></TABLE> <P><!-- ============ FIELD DETAIL =========== --><!-- ========= CONSTRUCTOR DETAIL ======== --><A NAME="constructor_detail"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TD COLSPAN=1><FONT SIZE="+2"><B>Constructor Detail</B></FONT></TD></TR></TABLE><A NAME="PhantomReference(java.lang.Object, java.lang.ref.ReferenceQueue)"><!-- --></A><H3>PhantomReference</H3><PRE>public <B>PhantomReference</B>(<A HREF="../../../java/lang/Object.html">Object</A> referent, <A HREF="../../../java/lang/ref/ReferenceQueue.html">ReferenceQueue</A> q)</PRE><DL><DD>Creates a new phantom reference that refers to the given object and is registered with the given queue.<DD><DL><DT><B>Throws:</B><DD><CODE><A HREF="../../../java/lang/NullPointerException.html">NullPointerException</A></CODE> - If the <code>queue</code> argument is <code>null</code></DL></DD></DL><!-- ============ METHOD DETAIL ========== --><A NAME="method_detail"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TD COLSPAN=1><FONT SIZE="+2"><B>Method Detail</B></FONT></TD></TR></TABLE><A NAME="get()"><!-- --></A><H3>get</H3><PRE>public <A HREF="../../../java/lang/Object.html">Object</A> <B>get</B>()</PRE><DL><DD>Returns this reference object's referent. Because the referent of a phantom reference is always inaccessible, this method always returns <code>null</code>.<DD><DL><DT><B>Overrides:</B><DD><CODE><A HREF="../../../java/lang/ref/Reference.html#get()">get</A></CODE> in class <CODE><A HREF="../../../java/lang/ref/Reference.html">Reference</A></CODE></DL></DD><DD><DL><DT><B>Returns:</B><DD><code>null</code></DL></DD></DL><!-- ========= END OF CLASS DATA ========= --><HR><!-- ========== START OF NAVBAR ========== --><A NAME="navbar_bottom"><!-- --></A><TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0"><TR><TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1"><A NAME="navbar_bottom_firstrow"><!-- --></A><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3"> <TR ALIGN="center" VALIGN="top"> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-summary.html"><FONT CLASS="NavBarFont1"><B>Package</B></FONT></A> </TD> <TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Class</B></FONT> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="class-use/PhantomReference.html"><FONT CLASS="NavBarFont1"><B>Use</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../index-files/index-1.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD> </TR></TABLE></TD><TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM><b>Java<sup><font size=-2>TM</font></sup> 2 Platform<br>Std. Ed. v1.3</b></EM></TD></TR><TR><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> PREV CLASS <A HREF="../../../java/lang/ref/Reference.html"><B>NEXT CLASS</B></A></FONT></TD><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../../index.html" TARGET="_top"><B>FRAMES</B></A> <A HREF="PhantomReference.html" TARGET="_top"><B>NO FRAMES</B></A></FONT></TD></TR><TR><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2"> SUMMARY: INNER | FIELD | <A HREF="#constructor_summary">CONSTR</A> | <A HREF="#method_summary">METHOD</A></FONT></TD><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">DETAIL: FIELD | <A HREF="#constructor_detail">CONSTR</A> | <A HREF="#method_detail">METHOD</A></FONT></TD></TR></TABLE><!-- =========== END OF NAVBAR =========== --><HR><font size="-1"><a href="http://java.sun.com/cgi-bin/bugreport.cgi">Submit a bug or feature</a><br>For further API reference and developer documentation, see <a href="http://java.sun.com/products/jdk/1.3/devdocs-vs-specs.html">Java 2 SDK SE Developer Documentation</a>. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples. <p>Java, Java 2D, and JDBC are trademarks or registered trademarks of Sun Microsystems, Inc. in the US and other countries.<br>Copyright 1993-2000 Sun Microsystems, Inc. 901 San Antonio Road<br>Palo Alto, California, 94303, U.S.A. All Rights Reserved.</font></BODY></HTML>⌨️ 快捷键说明
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