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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 23:35:23 PDT 2000 --><TITLE>Java 2 Platform SE v1.3: Class SoftReference</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/SoftReference.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"> <A HREF="../../../java/lang/ref/ReferenceQueue.html"><B>PREV CLASS</B></A> <A HREF="../../../java/lang/ref/WeakReference.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="SoftReference.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 SoftReference</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.SoftReference</B></PRE><HR><DL><DT>public class <B>SoftReference</B><DT>extends <A HREF="../../../java/lang/ref/Reference.html">Reference</A></DL><P>Soft reference objects, which are cleared at the discretion of the garbage collector in response to memory demand. Soft references are most often used to implement memory-sensitive caches. <p> Suppose that the garbage collector determines at a certain point in time that an object is <a href="package-summary.html#reachability">softly reachable</a>. At that time it may choose to clear atomically all soft references to that object and all soft references to any other softly-reachable objects from which that object is reachable through a chain of strong references. At the same time or at some later time it will enqueue those newly-cleared soft references that are registered with reference queues. <p> All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an <code>OutOfMemoryError</code>. Otherwise no constraints are placed upon the time at which a soft reference will be cleared or the order in which a set of such references to different objects will be cleared. Virtual machine implementations are, however, encouraged to bias against clearing recently-created or recently-used soft references. <p> Direct instances of this class may be used to implement simple caches; this class or derived subclasses may also be used in larger data structures to implement more sophisticated caches. As long as the referent of a soft reference is strongly reachable, that is, is actually in use, the soft reference will not be cleared. Thus a sophisticated cache can, for example, prevent its most recently used entries from being discarded by keeping strong referents to those entries, leaving the remaining entries to be discarded at the discretion of the garbage collector.<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/SoftReference.html#SoftReference(java.lang.Object)">SoftReference</A></B>(<A HREF="../../../java/lang/Object.html">Object</A> referent)</CODE><BR> Creates a new soft reference that refers to the given object.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><B><A HREF="../../../java/lang/ref/SoftReference.html#SoftReference(java.lang.Object, java.lang.ref.ReferenceQueue)">SoftReference</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 soft 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/SoftReference.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="SoftReference(java.lang.Object)"><!-- --></A><H3>SoftReference</H3><PRE>public <B>SoftReference</B>(<A HREF="../../../java/lang/Object.html">Object</A> referent)</PRE><DL><DD>Creates a new soft reference that refers to the given object. The new reference is not registered with any queue.</DL><HR><A NAME="SoftReference(java.lang.Object, java.lang.ref.ReferenceQueue)"><!-- --></A><H3>SoftReference</H3><PRE>public <B>SoftReference</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 soft 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. If this reference object has been cleared, either by the program or by the garbage collector, then this method 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>The object to which this reference refers, or <code>null</code> if this reference object has been cleared</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/SoftReference.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"> <A HREF="../../../java/lang/ref/ReferenceQueue.html"><B>PREV CLASS</B></A> <A HREF="../../../java/lang/ref/WeakReference.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="SoftReference.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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