IT. Expert System.

Java Standard Edition (SE)

JLabel


javax.swing

Class JLabel

  • All Implemented Interfaces:
    ImageObserver, MenuContainer, Serializable, Accessible, SwingConstants
    Direct Known Subclasses:
    BasicComboBoxRenderer, DefaultListCellRenderer, DefaultTableCellRenderer, DefaultTreeCellRenderer


    public class JLabel
    extends JComponent
    implements SwingConstants, Accessible
    A display area for a short text string or an image, or both. A label does not react to input events. As a result, it cannot get the keyboard focus. A label can, however, display a keyboard alternative as a convenience for a nearby component that has a keyboard alternative but can't display it.

    A JLabel object can display either text, an image, or both. You can specify where in the label's display area the label's contents are aligned by setting the vertical and horizontal alignment. By default, labels are vertically centered in their display area. Text-only labels are leading edge aligned, by default; image-only labels are horizontally centered, by default.

    You can also specify the position of the text relative to the image. By default, text is on the trailing edge of the image, with the text and image vertically aligned.

    A label's leading and trailing edge are determined from the value of its ComponentOrientation property. At present, the default ComponentOrientation setting maps the leading edge to left and the trailing edge to right.

    Finally, you can use the setIconTextGap method to specify how many pixels should appear between the text and the image. The default is 4 pixels.

    See How to Use Labels in The Java Tutorial for further documentation.

    Warning: Swing is not thread safe. For more information see Swing's Threading Policy.

    Warning: 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. As of 1.4, support for long term storage of all JavaBeans™ has been added to the java.beans package. Please see XMLEncoder.

    • Constructor Detail

      • JLabel

        public JLabel(String text,
                      Icon icon,
                      int horizontalAlignment)
        Creates a JLabel instance with the specified text, image, and horizontal alignment. The label is centered vertically in its display area. The text is on the trailing edge of the image.
        Parameters:
        text - The text to be displayed by the label.
        icon - The image to be displayed by the label.
        horizontalAlignment - One of the following constants defined in SwingConstants: LEFT, CENTER, RIGHT, LEADING or TRAILING.
      • JLabel

        public JLabel(String text,
                      int horizontalAlignment)
        Creates a JLabel instance with the specified text and horizontal alignment. The label is centered vertically in its display area.
        Parameters:
        text - The text to be displayed by the label.
        horizontalAlignment - One of the following constants defined in SwingConstants: LEFT, CENTER, RIGHT, LEADING or TRAILING.
      • JLabel

        public JLabel(String text)
        Creates a JLabel instance with the specified text. The label is aligned against the leading edge of its display area, and centered vertically.
        Parameters:
        text - The text to be displayed by the label.
      • JLabel

        public JLabel(Icon image,
                      int horizontalAlignment)
        Creates a JLabel instance with the specified image and horizontal alignment. The label is centered vertically in its display area.
        Parameters:
        image - The image to be displayed by the label.
        horizontalAlignment - One of the following constants defined in SwingConstants: LEFT, CENTER, RIGHT, LEADING or TRAILING.
      • JLabel

        public JLabel(Icon image)
        Creates a JLabel instance with the specified image. The label is centered vertically and horizontally in its display area.
        Parameters:
        image - The image to be displayed by the label.
      • JLabel

        public JLabel()
        Creates a JLabel instance with no image and with an empty string for the title. The label is centered vertically in its display area. The label's contents, once set, will be displayed on the leading edge of the label's display area.
    • Method Detail

      • getUI

        public LabelUI getUI()
        Returns the L&F object that renders this component.
        Returns:
        LabelUI object
      • getIcon

        public Icon getIcon()
        Returns the graphic image (glyph, icon) that the label displays.
        Returns:
        an Icon
        See Also:
        setIcon(javax.swing.Icon)
      • setDisabledIcon

        public void setDisabledIcon(Icon disabledIcon)
        Set the icon to be displayed if this JLabel is "disabled" (JLabel.setEnabled(false)).

        The default value of this property is null.

        Parameters:
        disabledIcon - the Icon to display when the component is disabled
        See Also:
        getDisabledIcon(), JComponent.setEnabled(boolean)
      • setDisplayedMnemonic

        public void setDisplayedMnemonic(int key)
        Specify a keycode that indicates a mnemonic key. This property is used when the label is part of a larger component. If the labelFor property of the label is not null, the label will call the requestFocus method of the component specified by the labelFor property when the mnemonic is activated.
        See Also:
        getLabelFor(), setLabelFor(java.awt.Component)
      • setDisplayedMnemonic

        public void setDisplayedMnemonic(char aChar)
        Specifies the displayedMnemonic as a char value.
        Parameters:
        aChar - a char specifying the mnemonic to display
        See Also:
        setDisplayedMnemonic(int)
      • getDisplayedMnemonic

        public int getDisplayedMnemonic()
        Return the keycode that indicates a mnemonic key. This property is used when the label is part of a larger component. If the labelFor property of the label is not null, the label will call the requestFocus method of the component specified by the labelFor property when the mnemonic is activated.
        Returns:
        int value for the mnemonic key
        See Also:
        getLabelFor(), setLabelFor(java.awt.Component)
      • setDisplayedMnemonicIndex

        public void setDisplayedMnemonicIndex(int index)
                                       throws IllegalArgumentException
        Provides a hint to the look and feel as to which character in the text should be decorated to represent the mnemonic. Not all look and feels may support this. A value of -1 indicates either there is no mnemonic, the mnemonic character is not contained in the string, or the developer does not wish the mnemonic to be displayed.

        The value of this is updated as the properties relating to the mnemonic change (such as the mnemonic itself, the text...). You should only ever have to call this if you do not wish the default character to be underlined. For example, if the text was 'Save As', with a mnemonic of 'a', and you wanted the 'A' to be decorated, as 'Save As', you would have to invoke setDisplayedMnemonicIndex(5) after invoking setDisplayedMnemonic(KeyEvent.VK_A).

        Parameters:
        index - Index into the String to underline
        Throws:
        IllegalArgumentException - will be thrown if index is >= length of the text, or < -1
        Since:
        1.4
      • getDisplayedMnemonicIndex

        public int getDisplayedMnemonicIndex()
        Returns the character, as an index, that the look and feel should provide decoration for as representing the mnemonic character.
        Returns:
        index representing mnemonic character
        Since:
        1.4
        See Also:
        setDisplayedMnemonicIndex(int)
      • getIconTextGap

        public int getIconTextGap()
        Returns the amount of space between the text and the icon displayed in this label.
        Returns:
        an int equal to the number of pixels between the text and the icon.
        See Also:
        setIconTextGap(int)
      • setIconTextGap

        public void setIconTextGap(int iconTextGap)
        If both the icon and text properties are set, this property defines the space between them.

        The default value of this property is 4 pixels.

        This is a JavaBeans bound property.

        See Also:
        getIconTextGap()
      • getVerticalAlignment

        public int getVerticalAlignment()
        Returns the alignment of the label's contents along the Y axis.
        Returns:
        The value of the verticalAlignment property, one of the following constants defined in SwingConstants: TOP, CENTER, or BOTTOM.
        See Also:
        SwingConstants, setVerticalAlignment(int)
      • setVerticalAlignment

        public void setVerticalAlignment(int alignment)
        Sets the alignment of the label's contents along the Y axis.

        The default value of this property is CENTER.

        Parameters:
        alignment - One of the following constants defined in SwingConstants: TOP, CENTER (the default), or BOTTOM.
        See Also:
        SwingConstants, getVerticalAlignment()
      • getHorizontalAlignment

        public int getHorizontalAlignment()
        Returns the alignment of the label's contents along the X axis.
        Returns:
        The value of the horizontalAlignment property, one of the following constants defined in SwingConstants: LEFT, CENTER, RIGHT, LEADING or TRAILING.
        See Also:
        setHorizontalAlignment(int), SwingConstants
      • setHorizontalAlignment

        public void setHorizontalAlignment(int alignment)
        Sets the alignment of the label's contents along the X axis.

        This is a JavaBeans bound property.

        Parameters:
        alignment - One of the following constants defined in SwingConstants: LEFT, CENTER (the default for image-only labels), RIGHT, LEADING (the default for text-only labels) or TRAILING.
        See Also:
        SwingConstants, getHorizontalAlignment()
      • getVerticalTextPosition

        public int getVerticalTextPosition()
        Returns the vertical position of the label's text, relative to its image.
        Returns:
        One of the following constants defined in SwingConstants: TOP, CENTER, or BOTTOM.
        See Also:
        setVerticalTextPosition(int), SwingConstants
      • setVerticalTextPosition

        public void setVerticalTextPosition(int textPosition)
        Sets the vertical position of the label's text, relative to its image.

        The default value of this property is CENTER.

        This is a JavaBeans bound property.

        Parameters:
        textPosition - One of the following constants defined in SwingConstants: TOP, CENTER (the default), or BOTTOM.
        See Also:
        SwingConstants, getVerticalTextPosition()
      • getHorizontalTextPosition

        public int getHorizontalTextPosition()
        Returns the horizontal position of the label's text, relative to its image.
        Returns:
        One of the following constants defined in SwingConstants: LEFT, CENTER, RIGHT, LEADING or TRAILING.
        See Also:
        SwingConstants
      • setHorizontalTextPosition

        public void setHorizontalTextPosition(int textPosition)
        Sets the horizontal position of the label's text, relative to its image.
        Parameters:
        textPosition - One of the following constants defined in SwingConstants: LEFT, CENTER, RIGHT, LEADING, or TRAILING (the default).
        Throws:
        IllegalArgumentException
        See Also:
        SwingConstants
      • imageUpdate

        public boolean imageUpdate(Image img,
                                   int infoflags,
                                   int x,
                                   int y,
                                   int w,
                                   int h)
        This is overridden to return false if the current Icon's Image is not equal to the passed in Image img.
        Specified by:
        imageUpdate in interface ImageObserver
        Overrides:
        imageUpdate in class Component
        Parameters:
        img - the image being observed
        infoflags - see imageUpdate for more information
        x - the x coordinate
        y - the y coordinate
        w - the width
        h - the height
        Returns:
        false if the infoflags indicate that the image is completely loaded; true otherwise.
        See Also:
        ImageObserver, Component.imageUpdate(java.awt.Image, int, int, int, int, int)
      • paramString

        protected String paramString()
        Returns a string representation of this JLabel. 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.
        Overrides:
        paramString in class JComponent
        Returns:
        a string representation of this JLabel.
      • getLabelFor

        public Component getLabelFor()
        Get the component this is labelling.
        Returns:
        the Component this is labelling. Can be null if this does not label a Component. If the displayedMnemonic property is set and the labelFor property is also set, the label will call the requestFocus method of the component specified by the labelFor property when the mnemonic is activated.
        See Also:
        getDisplayedMnemonic(), setDisplayedMnemonic(int)
      • setLabelFor

        public void setLabelFor(Component c)
        Set the component this is labelling. Can be null if this does not label a Component. If the displayedMnemonic property is set and the labelFor property is also set, the label will call the requestFocus method of the component specified by the labelFor property when the mnemonic is activated.
        Parameters:
        c - the Component this label is for, or null if the label is not the label for a component
        See Also:
        getDisplayedMnemonic(), setDisplayedMnemonic(int)


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