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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 23:36:58 PDT 2000 --><TITLE>Java 2 Platform SE v1.3: Class Observable</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/Observable.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/util/Locale.html"><B>PREV CLASS</B></A> <A HREF="../../java/util/Properties.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="Observable.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.util</FONT><BR>Class Observable</H2><PRE><A HREF="../../java/lang/Object.html">java.lang.Object</A> | +--<B>java.util.Observable</B></PRE><HR><DL><DT>public class <B>Observable</B><DT>extends <A HREF="../../java/lang/Object.html">Object</A></DL><P>This class represents an observable object, or "data" in the model-view paradigm. It can be subclassed to represent an object that the application wants to have observed. <p> An observable object can have one or more observers. An observer may be any object that implements interface <tt>Observer</tt>. After an observable instance changes, an application calling the <code>Observable</code>'s <code>notifyObservers</code> method causes all of its observers to be notified of the change by a call to their <code>update</code> method. <p> The order in which notifications will be delivered is unspecified. The default implementation provided in the Observerable class will notify Observers in the order in which they registered interest, but subclasses may change this order, use no guaranteed order, deliver notifications on separate threaads, or may guarantee that their subclass follows this order, as they choose. <p> Note that this notification mechanism is has nothing to do with threads and is completely separate from the <tt>wait</tt> and <tt>notify</tt> mechanism of class <tt>Object</tt>. <p> When an observable object is newly created, its set of observers is empty. Two observers are considered the same if and only if the <tt>equals</tt> method returns true for them.<P><DL><DT><B>Since: </B><DD>JDK1.0</DD><DT><B>See Also: </B><DD><A HREF="../../java/util/Observable.html#notifyObservers()"><CODE>notifyObservers()</CODE></A>, <A HREF="../../java/util/Observable.html#notifyObservers(java.lang.Object)"><CODE>notifyObservers(java.lang.Object)</CODE></A>, <A HREF="../../java/util/Observer.html"><CODE>Observer</CODE></A>, <A HREF="../../java/util/Observer.html#update(java.util.Observable, java.lang.Object)"><CODE>Observer.update(java.util.Observable, java.lang.Object)</CODE></A></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/util/Observable.html#Observable()">Observable</A></B>()</CODE><BR> Construct an Observable with zero Observers.</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> void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/Observable.html#addObserver(java.util.Observer)">addObserver</A></B>(<A HREF="../../java/util/Observer.html">Observer</A> o)</CODE><BR> Adds an observer to the set of observers for this object, provided that it is not the same as some observer already in the set.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE>protected void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/Observable.html#clearChanged()">clearChanged</A></B>()</CODE><BR> Indicates that this object has no longer changed, or that it has already notified all of its observers of its most recent change, so that the <tt>hasChanged</tt> method will now return <tt>false</tt>.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> int</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/Observable.html#countObservers()">countObservers</A></B>()</CODE><BR> Returns the number of observers of this <tt>Observable</tt> object.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/Observable.html#deleteObserver(java.util.Observer)">deleteObserver</A></B>(<A HREF="../../java/util/Observer.html">Observer</A> o)</CODE><BR> Deletes an observer from the set of observers of this object.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/Observable.html#deleteObservers()">deleteObservers</A></B>()</CODE><BR> Clears the observer list so that this object no longer has any observers.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> boolean</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/Observable.html#hasChanged()">hasChanged</A></B>()</CODE><BR> Tests if this object has changed.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/Observable.html#notifyObservers()">notifyObservers</A></B>()</CODE><BR> If this object has changed, as indicated by the <code>hasChanged</code> method, then notify all of its observers and then call the <code>clearChanged</code> method to indicate that this object has no longer changed.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/Observable.html#notifyObservers(java.lang.Object)">notifyObservers</A></B>(<A HREF="../../java/lang/Object.html">Object</A> arg)</CODE><BR> If this object has changed, as indicated by the <code>hasChanged</code> method, then notify all of its observers and then call the <code>clearChanged</code> method to indicate that this object has no longer changed.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE>protected void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/Observable.html#setChanged()">setChanged</A></B>()</CODE><BR> Marks this <tt>Observable</tt> object as having been changed; the <tt>hasChanged</tt> method will now return <tt>true</tt>.</TD>⌨️ 快捷键说明
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