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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 23:39:47 PDT 2000 --><TITLE>Java 2 Platform SE v1.3: Class JViewport</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/JViewport.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="../../javax/swing/JTree.TreeSelectionRedirector.html"><B>PREV CLASS</B></A> <A HREF="../../javax/swing/JViewport.AccessibleJViewport.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="JViewport.html" TARGET="_top"><B>NO FRAMES</B></A></FONT></TD></TR><TR><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2"> SUMMARY: <A HREF="#inner_class_summary">INNER</A> | <A HREF="#field_summary">FIELD</A> | <A HREF="#constructor_summary">CONSTR</A> | <A HREF="#method_summary">METHOD</A></FONT></TD><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">DETAIL: <A HREF="#field_detail">FIELD</A> | <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">javax.swing</FONT><BR>Class JViewport</H2><PRE><A HREF="../../java/lang/Object.html">java.lang.Object</A> | +--<A HREF="../../java/awt/Component.html">java.awt.Component</A> | +--<A HREF="../../java/awt/Container.html">java.awt.Container</A> | +--<A HREF="../../javax/swing/JComponent.html">javax.swing.JComponent</A> | +--<B>javax.swing.JViewport</B></PRE><DL><DT><B>All Implemented Interfaces:</B> <DD><A HREF="../../javax/accessibility/Accessible.html">Accessible</A>, <A HREF="../../java/awt/image/ImageObserver.html">ImageObserver</A>, <A HREF="../../java/awt/MenuContainer.html">MenuContainer</A>, <A HREF="../../java/io/Serializable.html">Serializable</A></DD></DL><HR><DL><DT>public class <B>JViewport</B><DT>extends <A HREF="../../javax/swing/JComponent.html">JComponent</A><DT>implements <A HREF="../../javax/accessibility/Accessible.html">Accessible</A></DL><P>The "viewport" or "porthole" through which you see the underlying information. When you scroll, what moves is the viewport. It is like peering through a camera's viewfinder. Moving the viewfinder upwards brings new things into view at the top of the picture and loses things that were at the bottom. <p> By default, <code>JViewport</code> is opaque. To change this, use the <code>setOpaque</code> method. <p> <b>NOTE:</b>We have implemented a faster scrolling algorithm that does not require a buffer to draw in. The algorithm works as follows: <ol><li>The view and parent view and checked to see if they are <code>JComponents</code>, if they aren't, stop and repaint the whole viewport. <li>If the viewport is obscured by an ancestor, stop and repaint the whole viewport. <li>Compute the region that will become visible, if it is as big as the viewport, stop and repaint the whole view region. <li>Obtain the ancestor Windows graphics and do a <code>copyArea</code> on the scrolled region. <li>Message the view to repaint the newly visible region. <li>The next time paint is invoked on the viewport, if the clip region is smaller than the viewport size a timer is kicked off to repaint the whole region. </ol> In general this approach is much faster. Compared to the backing store approach this avoids the overhead of maintaining an offscreen buffer and having to do two <code>copyArea</code>s. Compared to the non backing store case this approach will greatly reduce the painted region. <p> This approach can cause slower times than the backing store approach when the viewport is obscured by another window, or partially offscreen. When another window obscures the viewport the copyArea will copy garbage and a paint event will be generated by the system to inform us we need to paint the newly exposed region. The only way to handle this is to repaint the whole viewport, which can cause slower performance than the backing store case. In most applications very rarely will the user be scrolling while the viewport is obscured by another window or offscreen, so this optimization is usually worth the performance hit when obscured. <strong>Warning:</strong> Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. A future release of Swing will provide support for long term persistence.<P><DL><DT><B>See Also: </B><DD><A HREF="../../javax/swing/JScrollPane.html"><CODE>JScrollPane</CODE></A>, <A HREF="../../serialized-form.html#javax.swing.JViewport">Serialized Form</A></DL><HR><P><!-- ======== INNER CLASS SUMMARY ======== --><A NAME="inner_class_summary"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TD COLSPAN=2><FONT SIZE="+2"><B>Inner Class Summary</B></FONT></TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE>protected class</CODE></FONT></TD><TD><CODE><B><A HREF="../../javax/swing/JViewport.AccessibleJViewport.html">JViewport.AccessibleJViewport</A></B></CODE><BR> This class implements accessibility support for the <code>JViewport</code> class.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE>protected class</CODE></FONT></TD><TD><CODE><B><A HREF="../../javax/swing/JViewport.ViewListener.html">JViewport.ViewListener</A></B></CODE><BR> A listener for the view.</TD></TR></TABLE> <A NAME="inner_classes_inherited_from_class_javax.swing.JComponent"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor"><TD><B>Inner classes inherited from class javax.swing.<A HREF="../../javax/swing/JComponent.html">JComponent</A></B></TD>⌨️ 快捷键说明
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