Class JLabel

java.lang.Object
java.awt.Component
java.awt.Container
javax.swing.JComponent
javax.swing.JLabel
All Implemented Interfaces:
ImageObserver, MenuContainer, Serializable, Accessible, SwingConstants
Direct Known Subclasses:
BasicComboBoxRenderer, DefaultListCellRenderer, DefaultTableCellRenderer, DefaultTreeCellRenderer
@JavaBean(defaultProperty="UI", description="A component that displays a short string and an icon.") 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.

Since:
1.2

  • Field Details

    • labelFor

      protected Component labelFor
      The Component this label is for; null if the label is not the label for a component

  • Constructor Details

    • 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 Details

    • getUI

      public LabelUI getUI()
      Returns the L&F object that renders this component.
      Overrides:
      getUI in class JComponent
      Returns:
      LabelUI object

    • setUI

      @BeanProperty(hidden=true, visualUpdate=true, description="The UI object that implements the Component's LookAndFeel.") public void setUI(LabelUI ui)
      Sets the L&F object that renders this component.
      Parameters:
      ui - the LabelUI L&F object
      See Also:

    • updateUI

      public void updateUI()
      Resets the UI property to a value from the current look and feel.
      Overrides:
      updateUI in class JComponent
      See Also:

    • getUIClassID

      @BeanProperty(bound=false) public String getUIClassID()
      Returns a string that specifies the name of the l&f class that renders this component.
      Overrides:
      getUIClassID in class JComponent
      Returns:
      the string "LabelUI"
      See Also:

    • getText

      public String getText()
      Returns the text string that the label displays.
      Returns:
      a String
      See Also:

    • setText

      @BeanProperty(preferred=true, visualUpdate=true, description="Defines the single line of text this component will display.") public void setText(String text)
      Defines the single line of text this component will display. If the value of text is null or empty string, nothing is displayed.

      The default value of this property is null.

      This is a JavaBeans bound property.

      Parameters:
      text - the single line of text this component will display
      See Also:

    • getIcon

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

    • setIcon

      @BeanProperty(preferred=true, visualUpdate=true, description="The icon this component will display.") public void setIcon(Icon icon)
      Defines the icon this component will display. If the value of icon is null, nothing is displayed.

      The default value of this property is null.

      This is a JavaBeans bound property.

      Parameters:
      icon - the default icon this component will display
      See Also:

    • getDisabledIcon

      public Icon getDisabledIcon()
      Returns the icon used by the label when it's disabled. If no disabled icon has been set this will forward the call to the look and feel to construct an appropriate disabled Icon.

      Some look and feels might not render the disabled Icon, in which case they will ignore this.

      Returns:
      the disabledIcon property
      See Also:

    • setDisabledIcon

      @BeanProperty(visualUpdate=true, description="The icon to display if the label is disabled.") 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:

    • setDisplayedMnemonic

      @BeanProperty(visualUpdate=true, description="The mnemonic keycode.") 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.
      Parameters:
      key - a keycode that indicates a mnemonic key
      See Also:

    • setDisplayedMnemonic

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

    • 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:

    • setDisplayedMnemonicIndex

      @BeanProperty(visualUpdate=true, description="the index into the String to draw the keyboard character mnemonic at") 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:

    • checkHorizontalKey

      protected int checkHorizontalKey(int key, String message)
      Verify that key is a legal value for the horizontalAlignment properties.
      Parameters:
      key - the property value to check
      message - the IllegalArgumentException detail message
      Returns:
      the key value if key is a legal value for the horizontalAlignment properties
      Throws:
      IllegalArgumentException - if key isn't LEFT, CENTER, RIGHT, LEADING or TRAILING.
      See Also:

    • checkVerticalKey

      protected int checkVerticalKey(int key, String message)
      Verify that key is a legal value for the verticalAlignment or verticalTextPosition properties.
      Parameters:
      key - the property value to check
      message - the IllegalArgumentException detail message
      Returns:
      the key value if key is a legal value for the verticalAlignment or verticalTextPosition properties
      Throws:
      IllegalArgumentException - if key isn't TOP, CENTER, or BOTTOM.
      See Also:

    • 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

      @BeanProperty(visualUpdate=true, description="If both the icon and text properties are set, this property defines the space between them.") 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.

      Parameters:
      iconTextGap - the space between the icon and text properties
      See Also:

    • 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:

    • setVerticalAlignment

      @BeanProperty(visualUpdate=true, enumerationValues={"SwingConstants.TOP","SwingConstants.CENTER","SwingConstants.BOTTOM"}, description="The alignment of the label's contents along the Y axis.") 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:

    • 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

      @BeanProperty(visualUpdate=true, enumerationValues={"SwingConstants.LEFT","SwingConstants.CENTER","SwingConstants.RIGHT","SwingConstants.LEADING","SwingConstants.TRAILING"}, description="The alignment of the label's content along the X axis.") 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:

    • 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

      @BeanProperty(expert=true, visualUpdate=true, enumerationValues={"SwingConstants.TOP","SwingConstants.CENTER","SwingConstants.BOTTOM"}, description="The vertical position of the text relative to it's image.") 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:

    • 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:

    • setHorizontalTextPosition

      @BeanProperty(expert=true, visualUpdate=true, enumerationValues={"SwingConstants.LEFT","SwingConstants.CENTER","SwingConstants.RIGHT","SwingConstants.LEADING","SwingConstants.TRAILING"}, description="The horizontal position of the label's text, relative to its image.") 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).
      See Also:

    • imageUpdate

      public boolean imageUpdate(Image img, int infoflags, int x, int y, int w, int h)
      If the component is not showing or either the icon or disabled icon is not an ImageIcon with an Image equal to the passed in Image, return false; otherwise it will delegate to the super-class.
      Specified by:
      imageUpdate in interface ImageObserver
      Overrides:
      imageUpdate in class Component
      Parameters:
      img - the Image to be compared
      infoflags - flags used to repaint the label when the image is updated and which determine how much is to be painted
      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:

    • 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:

    • setLabelFor

      @BeanProperty(description="The component this is labelling.") 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:

    • getAccessibleContext

      @BeanProperty(bound=false, expert=true, description="The AccessibleContext associated with this Label.") public AccessibleContext getAccessibleContext()
      Get the AccessibleContext of this object
      Specified by:
      getAccessibleContext in interface Accessible
      Overrides:
      getAccessibleContext in class Component
      Returns:
      the AccessibleContext of this object