001: /*
002: * Copyright 1995-2006 Sun Microsystems, Inc. All Rights Reserved.
003: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004: *
005: * This code is free software; you can redistribute it and/or modify it
006: * under the terms of the GNU General Public License version 2 only, as
007: * published by the Free Software Foundation. Sun designates this
008: * particular file as subject to the "Classpath" exception as provided
009: * by Sun in the LICENSE file that accompanied this code.
010: *
011: * This code is distributed in the hope that it will be useful, but WITHOUT
012: * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013: * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014: * version 2 for more details (a copy is included in the LICENSE file that
015: * accompanied this code).
016: *
017: * You should have received a copy of the GNU General Public License version
018: * 2 along with this work; if not, write to the Free Software Foundation,
019: * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020: *
021: * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022: * CA 95054 USA or visit www.sun.com if you need additional information or
023: * have any questions.
024: */
025: package java.awt;
026:
027: import java.awt.peer.LabelPeer;
028: import java.io.IOException;
029: import java.io.ObjectInputStream;
030: import javax.accessibility.*;
031:
032: /**
033: * A <code>Label</code> object is a component for placing text in a
034: * container. A label displays a single line of read-only text.
035: * The text can be changed by the application, but a user cannot edit it
036: * directly.
037: * <p>
038: * For example, the code . . .
039: * <p>
040: * <hr><blockquote><pre>
041: * setLayout(new FlowLayout(FlowLayout.CENTER, 10, 10));
042: * add(new Label("Hi There!"));
043: * add(new Label("Another Label"));
044: * </pre></blockquote><hr>
045: * <p>
046: * produces the following labels:
047: * <p>
048: * <img src="doc-files/Label-1.gif" alt="Two labels: 'Hi There!' and 'Another label'"
049: * ALIGN=center HSPACE=10 VSPACE=7>
050: *
051: * @version 1.66, 05/05/07
052: * @author Sami Shaio
053: * @since JDK1.0
054: */
055: public class Label extends Component implements Accessible {
056:
057: static {
058: /* ensure that the necessary native libraries are loaded */
059: Toolkit.loadLibraries();
060: if (!GraphicsEnvironment.isHeadless()) {
061: initIDs();
062: }
063: }
064:
065: /**
066: * Indicates that the label should be left justified.
067: */
068: public static final int LEFT = 0;
069:
070: /**
071: * Indicates that the label should be centered.
072: */
073: public static final int CENTER = 1;
074:
075: /**
076: * Indicates that the label should be right justified.
077: * @since JDK1.0t.
078: */
079: public static final int RIGHT = 2;
080:
081: /**
082: * The text of this label.
083: * This text can be modified by the program
084: * but never by the user.
085: *
086: * @serial
087: * @see #getText()
088: * @see #setText(String)
089: */
090: String text;
091:
092: /**
093: * The label's alignment. The default alignment is set
094: * to be left justified.
095: *
096: * @serial
097: * @see #getAlignment()
098: * @see #setAlignment(int)
099: */
100: int alignment = LEFT;
101:
102: private static final String base = "label";
103: private static int nameCounter = 0;
104:
105: /*
106: * JDK 1.1 serialVersionUID
107: */
108: private static final long serialVersionUID = 3094126758329070636L;
109:
110: /**
111: * Constructs an empty label.
112: * The text of the label is the empty string <code>""</code>.
113: * @exception HeadlessException if GraphicsEnvironment.isHeadless()
114: * returns true.
115: * @see java.awt.GraphicsEnvironment#isHeadless
116: */
117: public Label() throws HeadlessException {
118: this ("", LEFT);
119: }
120:
121: /**
122: * Constructs a new label with the specified string of text,
123: * left justified.
124: * @param text the string that the label presents.
125: * A <code>null</code> value
126: * will be accepted without causing a NullPointerException
127: * to be thrown.
128: * @exception HeadlessException if GraphicsEnvironment.isHeadless()
129: * returns true.
130: * @see java.awt.GraphicsEnvironment#isHeadless
131: */
132: public Label(String text) throws HeadlessException {
133: this (text, LEFT);
134: }
135:
136: /**
137: * Constructs a new label that presents the specified string of
138: * text with the specified alignment.
139: * Possible values for <code>alignment</code> are <code>Label.LEFT</code>,
140: * <code>Label.RIGHT</code>, and <code>Label.CENTER</code>.
141: * @param text the string that the label presents.
142: * A <code>null</code> value
143: * will be accepted without causing a NullPointerException
144: * to be thrown.
145: * @param alignment the alignment value.
146: * @exception HeadlessException if GraphicsEnvironment.isHeadless()
147: * returns true.
148: * @see java.awt.GraphicsEnvironment#isHeadless
149: */
150: public Label(String text, int alignment) throws HeadlessException {
151: GraphicsEnvironment.checkHeadless();
152: this .text = text;
153: setAlignment(alignment);
154: }
155:
156: /**
157: * Read a label from an object input stream.
158: * @exception HeadlessException if
159: * <code>GraphicsEnvironment.isHeadless()</code> returns
160: * <code>true</code>
161: * @serial
162: * @since 1.4
163: * @see java.awt.GraphicsEnvironment#isHeadless
164: */
165: private void readObject(ObjectInputStream s)
166: throws ClassNotFoundException, IOException,
167: HeadlessException {
168: GraphicsEnvironment.checkHeadless();
169: s.defaultReadObject();
170: }
171:
172: /**
173: * Construct a name for this component. Called by getName() when the
174: * name is <code>null</code>.
175: */
176: String constructComponentName() {
177: synchronized (Label.class) {
178: return base + nameCounter++;
179: }
180: }
181:
182: /**
183: * Creates the peer for this label. The peer allows us to
184: * modify the appearance of the label without changing its
185: * functionality.
186: */
187: public void addNotify() {
188: synchronized (getTreeLock()) {
189: if (peer == null)
190: peer = getToolkit().createLabel(this );
191: super .addNotify();
192: }
193: }
194:
195: /**
196: * Gets the current alignment of this label. Possible values are
197: * <code>Label.LEFT</code>, <code>Label.RIGHT</code>, and
198: * <code>Label.CENTER</code>.
199: * @see java.awt.Label#setAlignment
200: */
201: public int getAlignment() {
202: return alignment;
203: }
204:
205: /**
206: * Sets the alignment for this label to the specified alignment.
207: * Possible values are <code>Label.LEFT</code>,
208: * <code>Label.RIGHT</code>, and <code>Label.CENTER</code>.
209: * @param alignment the alignment to be set.
210: * @exception IllegalArgumentException if an improper value for
211: * <code>alignment</code> is given.
212: * @see java.awt.Label#getAlignment
213: */
214: public synchronized void setAlignment(int alignment) {
215: switch (alignment) {
216: case LEFT:
217: case CENTER:
218: case RIGHT:
219: this .alignment = alignment;
220: LabelPeer peer = (LabelPeer) this .peer;
221: if (peer != null) {
222: peer.setAlignment(alignment);
223: }
224: return;
225: }
226: throw new IllegalArgumentException("improper alignment: "
227: + alignment);
228: }
229:
230: /**
231: * Gets the text of this label.
232: * @return the text of this label, or <code>null</code> if
233: * the text has been set to <code>null</code>.
234: * @see java.awt.Label#setText
235: */
236: public String getText() {
237: return text;
238: }
239:
240: /**
241: * Sets the text for this label to the specified text.
242: * @param text the text that this label displays. If
243: * <code>text</code> is <code>null</code>, it is
244: * treated for display purposes like an empty
245: * string <code>""</code>.
246: * @see java.awt.Label#getText
247: */
248: public void setText(String text) {
249: boolean testvalid = false;
250: synchronized (this ) {
251: if (text != this .text
252: && (this .text == null || !this .text.equals(text))) {
253: this .text = text;
254: LabelPeer peer = (LabelPeer) this .peer;
255: if (peer != null) {
256: peer.setText(text);
257: }
258: testvalid = true;
259: }
260: }
261:
262: // This could change the preferred size of the Component.
263: if (testvalid && valid) {
264: invalidate();
265: }
266: }
267:
268: /**
269: * Returns a string representing the state of this <code>Label</code>.
270: * This method is intended to be used only for debugging purposes, and the
271: * content and format of the returned string may vary between
272: * implementations. The returned string may be empty but may not be
273: * <code>null</code>.
274: *
275: * @return the parameter string of this label
276: */
277: protected String paramString() {
278: String str = ",align=";
279: switch (alignment) {
280: case LEFT:
281: str += "left";
282: break;
283: case CENTER:
284: str += "center";
285: break;
286: case RIGHT:
287: str += "right";
288: break;
289: }
290: return super .paramString() + str + ",text=" + text;
291: }
292:
293: /**
294: * Initialize JNI field and method IDs
295: */
296: private static native void initIDs();
297:
298: /////////////////
299: // Accessibility support
300: ////////////////
301:
302: /**
303: * Gets the AccessibleContext associated with this Label.
304: * For labels, the AccessibleContext takes the form of an
305: * AccessibleAWTLabel.
306: * A new AccessibleAWTLabel instance is created if necessary.
307: *
308: * @return an AccessibleAWTLabel that serves as the
309: * AccessibleContext of this Label
310: * @since 1.3
311: */
312: public AccessibleContext getAccessibleContext() {
313: if (accessibleContext == null) {
314: accessibleContext = new AccessibleAWTLabel();
315: }
316: return accessibleContext;
317: }
318:
319: /**
320: * This class implements accessibility support for the
321: * <code>Label</code> class. It provides an implementation of the
322: * Java Accessibility API appropriate to label user-interface elements.
323: * @since 1.3
324: */
325: protected class AccessibleAWTLabel extends AccessibleAWTComponent {
326: /*
327: * JDK 1.3 serialVersionUID
328: */
329: private static final long serialVersionUID = -3568967560160480438L;
330:
331: public AccessibleAWTLabel() {
332: super ();
333: }
334:
335: /**
336: * Get the accessible name of this object.
337: *
338: * @return the localized name of the object -- can be null if this
339: * object does not have a name
340: * @see AccessibleContext#setAccessibleName
341: */
342: public String getAccessibleName() {
343: if (accessibleName != null) {
344: return accessibleName;
345: } else {
346: if (getText() == null) {
347: return super .getAccessibleName();
348: } else {
349: return getText();
350: }
351: }
352: }
353:
354: /**
355: * Get the role of this object.
356: *
357: * @return an instance of AccessibleRole describing the role of the object
358: * @see AccessibleRole
359: */
360: public AccessibleRole getAccessibleRole() {
361: return AccessibleRole.LABEL;
362: }
363:
364: } // inner class AccessibleAWTLabel
365:
366: }
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