JDK8/Java8源码在线阅读
/*
* Copyright (c) 1995, 2014, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.awt;
import java.awt.peer.LabelPeer;
import java.io.IOException;
import java.io.ObjectInputStream;
import javax.accessibility.*;
/**
* A <code>Label</code> object is a component for placing text in a
* container. A label displays a single line of read-only text.
* The text can be changed by the application, but a user cannot edit it
* directly.
* <p>
* For example, the code . . .
*
* <hr><blockquote><pre>
* setLayout(new FlowLayout(FlowLayout.CENTER, 10, 10));
* add(new Label("Hi There!"));
* add(new Label("Another Label"));
* </pre></blockquote><hr>
* <p>
* produces the following labels:
* <p>
* <img src="doc-files/Label-1.gif" alt="Two labels: 'Hi There!' and 'Another label'"
* style="float:center; margin: 7px 10px;">
*
* @author Sami Shaio
* @since JDK1.0
*/
public class Label extends Component implements Accessible {
static {
/* ensure that the necessary native libraries are loaded */
Toolkit.loadLibraries();
if (!GraphicsEnvironment.isHeadless()) {
initIDs();
}
}
/**
* Indicates that the label should be left justified.
*/
public static final int LEFT = 0;
/**
* Indicates that the label should be centered.
*/
public static final int CENTER = 1;
/**
* Indicates that the label should be right justified.
* @since JDK1.0t.
*/
public static final int RIGHT = 2;
/**
* The text of this label.
* This text can be modified by the program
* but never by the user.
*
* @serial
* @see #getText()
* @see #setText(String)
*/
String text;
/**
* The label's alignment. The default alignment is set
* to be left justified.
*
* @serial
* @see #getAlignment()
* @see #setAlignment(int)
*/
int alignment = LEFT;
private static final String base = "label";
private static int nameCounter = 0;
/*
* JDK 1.1 serialVersionUID
*/
private static final long serialVersionUID = 3094126758329070636L;
/**
* Constructs an empty label.
* The text of the label is the empty string <code>""</code>.
* @exception HeadlessException if GraphicsEnvironment.isHeadless()
* returns true.
* @see java.awt.GraphicsEnvironment#isHeadless
*/
public Label() throws HeadlessException {
this("", LEFT);
}
/**
* Constructs a new label with the specified string of text,
* left justified.
* @param text the string that the label presents.
* A <code>null</code> value
* will be accepted without causing a NullPointerException
* to be thrown.
* @exception HeadlessException if GraphicsEnvironment.isHeadless()
* returns true.
* @see java.awt.GraphicsEnvironment#isHeadless
*/
public Label(String text) throws HeadlessException {
this(text, LEFT);
}
/**
* Constructs a new label that presents the specified string of
* text with the specified alignment.
* Possible values for <code>alignment</code> are <code>Label.LEFT</code>,
* <code>Label.RIGHT</code>, and <code>Label.CENTER</code>.
* @param text the string that the label presents.
* A <code>null</code> value
* will be accepted without causing a NullPointerException
* to be thrown.
* @param alignment the alignment value.
* @exception HeadlessException if GraphicsEnvironment.isHeadless()
* returns true.
* @see java.awt.GraphicsEnvironment#isHeadless
*/
public Label(String text, int alignment) throws HeadlessException {
GraphicsEnvironment.checkHeadless();
this.text = text;
setAlignment(alignment);
}
/**
* Read a label from an object input stream.
* @exception HeadlessException if
* <code>GraphicsEnvironment.isHeadless()</code> returns
* <code>true</code>
* @serial
* @since 1.4
* @see java.awt.GraphicsEnvironment#isHeadless
*/
private void readObject(ObjectInputStream s)
throws ClassNotFoundException, IOException, HeadlessException {
GraphicsEnvironment.checkHeadless();
s.defaultReadObject();
}
/**
* Construct a name for this component. Called by getName() when the
* name is <code>null</code>.
*/
String constructComponentName() {
synchronized (Label.class) {
return base + nameCounter++;
}
}
/**
* Creates the peer for this label. The peer allows us to
* modify the appearance of the label without changing its
* functionality.
*/
public void addNotify() {
synchronized (getTreeLock()) {
if (peer == null)
peer = getToolkit().createLabel(this);
super.addNotify();
}
}
/**
* Gets the current alignment of this label. Possible values are
* <code>Label.LEFT</code>, <code>Label.RIGHT</code>, and
* <code>Label.CENTER</code>.
* @see java.awt.Label#setAlignment
*/
public int getAlignment() {
return alignment;
}
/**
* Sets the alignment for this label to the specified alignment.
* Possible values are <code>Label.LEFT</code>,
* <code>Label.RIGHT</code>, and <code>Label.CENTER</code>.
* @param alignment the alignment to be set.
* @exception IllegalArgumentException if an improper value for
* <code>alignment</code> is given.
* @see java.awt.Label#getAlignment
*/
public synchronized void setAlignment(int alignment) {
switch (alignment) {
case LEFT:
case CENTER:
case RIGHT:
this.alignment = alignment;
LabelPeer peer = (LabelPeer)this.peer;
if (peer != null) {
peer.setAlignment(alignment);
}
return;
}
throw new IllegalArgumentException("improper alignment: " + alignment);
}
/**
* Gets the text of this label.
* @return the text of this label, or <code>null</code> if
* the text has been set to <code>null</code>.
* @see java.awt.Label#setText
*/
public String getText() {
return text;
}
/**
* Sets the text for this label to the specified text.
* @param text the text that this label displays. If
* <code>text</code> is <code>null</code>, it is
* treated for display purposes like an empty
* string <code>""</code>.
* @see java.awt.Label#getText
*/
public void setText(String text) {
boolean testvalid = false;
synchronized (this) {
if (text != this.text && (this.text == null ||
!this.text.equals(text))) {
this.text = text;
LabelPeer peer = (LabelPeer)this.peer;
if (peer != null) {
peer.setText(text);
}
testvalid = true;
}
}
// This could change the preferred size of the Component.
if (testvalid) {
invalidateIfValid();
}
}
/**
* Returns a string representing the state of this <code>Label</code>.
* This method is intended to be used only for debugging purposes, and the
* content and format of the returned string may vary between
* implementations. The returned string may be empty but may not be
* <code>null</code>.
*
* @return the parameter string of this label
*/
protected String paramString() {
String align = "";
switch (alignment) {
case LEFT: align = "left"; break;
case CENTER: align = "center"; break;
case RIGHT: align = "right"; break;
}
return super.paramString() + ",align=" + align + ",text=" + text;
}
/**
* Initialize JNI field and method IDs
*/
private static native void initIDs();
/////////////////
// Accessibility support
////////////////
/**
* Gets the AccessibleContext associated with this Label.
* For labels, the AccessibleContext takes the form of an
* AccessibleAWTLabel.
* A new AccessibleAWTLabel instance is created if necessary.
*
* @return an AccessibleAWTLabel that serves as the
* AccessibleContext of this Label
* @since 1.3
*/
public AccessibleContext getAccessibleContext() {
if (accessibleContext == null) {
accessibleContext = new AccessibleAWTLabel();
}
return accessibleContext;
}
/**
* This class implements accessibility support for the
* <code>Label</code> class. It provides an implementation of the
* Java Accessibility API appropriate to label user-interface elements.
* @since 1.3
*/
protected class AccessibleAWTLabel extends AccessibleAWTComponent
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