https://openjdk.java.net/ 
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package java.awt;

import java.awt.peer.LabelPeer;
import java.io.IOException;
import java.io.ObjectInputStream;
import javax.accessibility.*;


A Label 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. 

For example, the code . . .

setLayout(new FlowLayout(FlowLayout.CENTER, 10, 10));
add(new Label("Hi There!"));
add(new Label("Another Label"));




produces the following labels:




Author:     Sami Shaio
Since:      1.0
/**
 * A {@code Label} 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&nbsp;.&nbsp;.&nbsp;.
 *
 * <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       1.0
 */
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.

/**
     * Indicates that the label should be left justified.
     */
    public static final int LEFT        = 0;

    
Indicates that the label should be centered.

/**
     * Indicates that the label should be centered.
     */
    public static final int CENTER      = 1;

    
Indicates that the label should be right justified.

/**
     * Indicates that the label should be right justified.
     */
    public static final int RIGHT       = 2;

    
The text of this label.
This text can be modified by the program
but never by the user.

See Also:
@serial
/**
     * 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.

See Also:
@serial
/**
     * 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 "". 
Throws:
See Also:
/**
     * Constructs an empty label.
     * The text of the label is the empty string {@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.

Params:
  • text – the string that the label presents. A null value will be accepted without causing a NullPointerException to be thrown.
Throws:
See Also:
/**
     * Constructs a new label with the specified string of text,
     * left justified.
     * @param text the string that the label presents.
     *        A {@code null} 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 alignment are Label.LEFT, Label.RIGHT, and Label.CENTER. 
Params:
  • text – the string that the label presents. A null value will be accepted without causing a NullPointerException to be thrown.
  • alignment –   the alignment value.
Throws:
See Also:
/**
     * Constructs a new label that presents the specified string of
     * text with the specified alignment.
     * Possible values for {@code alignment} are {@code Label.LEFT},
     * {@code Label.RIGHT}, and {@code Label.CENTER}.
     * @param text the string that the label presents.
     *        A {@code null} 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.

Throws:
  • HeadlessException – if GraphicsEnvironment.isHeadless() returns true
See Also:
@serial
Since:1.4
/**
     * Read a label from an object input stream.
     * @exception HeadlessException if
     * {@code GraphicsEnvironment.isHeadless()} returns
     * {@code true}
     * @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 null. 
/**
     * Construct a name for this component.  Called by getName() when the
     * name is {@code null}.
     */
    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.

/**
     * 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 = getComponentFactory().createLabel(this);
            super.addNotify();
        }
    }

    
Gets the current alignment of this label. Possible values are Label.LEFT, Label.RIGHT, and Label.CENTER. 
See Also:
Returns:the alignment of this label
/**
     * Gets the current alignment of this label. Possible values are
     * {@code Label.LEFT}, {@code Label.RIGHT}, and
     * {@code Label.CENTER}.
     * @return the alignment of this label
     * @see java.awt.Label#setAlignment
     */
    public int getAlignment() {
        return alignment;
    }

    
Sets the alignment for this label to the specified alignment. Possible values are Label.LEFT, Label.RIGHT, and Label.CENTER. 
Params:
  • alignment –    the alignment to be set.
Throws:
See Also:
/**
     * Sets the alignment for this label to the specified alignment.
     * Possible values are {@code Label.LEFT},
     * {@code Label.RIGHT}, and {@code Label.CENTER}.
     * @param      alignment    the alignment to be set.
     * @exception  IllegalArgumentException if an improper value for
     *                          {@code alignment} 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.

See Also:
Returns: the text of this label, or null if the text has been set to null.
/**
     * Gets the text of this label.
     * @return     the text of this label, or {@code null} if
     *             the text has been set to {@code null}.
     * @see        java.awt.Label#setText
     */
    public String getText() {
        return text;
    }

    
Sets the text for this label to the specified text.

Params:
  • text – the text that this label displays. If text is null, it is treated for display purposes like an empty string "".
See Also:
/**
     * Sets the text for this label to the specified text.
     * @param      text the text that this label displays. If
     *             {@code text} is {@code null}, it is
     *             treated for display purposes like an empty
     *             string {@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 Label. 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 null. 
Returns:    the parameter string of this label
/**
     * Returns a string representing the state of this {@code Label}.
     * 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}.
     *
     * @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

/**
     * 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.

Returns:an AccessibleAWTLabel that serves as the
        AccessibleContext of this Label
Since:1.3
/**
     * 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 Label class. It provides an implementation of the Java Accessibility API appropriate to label user-interface elements. 
Since:1.3
/**
     * This class implements accessibility support for the
     * {@code Label} class.  It provides an implementation of the
     * Java Accessibility API appropriate to label user-interface elements.
     * @since 1.3
     */
    protected class AccessibleAWTLabel extends AccessibleAWTComponent
    {
        /*
         * JDK 1.3 serialVersionUID
         */
        private static final long serialVersionUID = -3568967560160480438L;

        
Constructor for the accessible label.

/**
         * Constructor for the accessible label.
         */
        public AccessibleAWTLabel() {
            super();
        }

        
Get the accessible name of this object.

See Also:
Returns:the localized name of the object -- can be null if this
object does not have a name
/**
         * Get the accessible name of this object.
         *
         * @return the localized name of the object -- can be null if this
         * object does not have a name
         * @see AccessibleContext#setAccessibleName
         */
        public String getAccessibleName() {
            if (accessibleName != null) {
                return accessibleName;
            } else {
                if (getText() == null) {
                    return super.getAccessibleName();
                } else {
                    return getText();
                }
            }
        }

        
Get the role of this object.

See Also:
Returns:an instance of AccessibleRole describing the role of the object
/**
         * Get the role of this object.
         *
         * @return an instance of AccessibleRole describing the role of the object
         * @see AccessibleRole
         */
        public AccessibleRole getAccessibleRole() {
            return AccessibleRole.LABEL;
        }

    } // inner class AccessibleAWTLabel

}