Module java.desktop
Package java.awt

Class ScrollPane

java.lang.Object
java.awt.Component
java.awt.Container
java.awt.ScrollPane
All Implemented Interfaces:
ImageObserver, MenuContainer, Serializable, Accessible
public class ScrollPane
extends Container
implements Accessible
A container class which implements automatic horizontal and/or vertical scrolling for a single child component. The display policy for the scrollbars can be set to:
  1. as needed: scrollbars created and shown only when needed by scrollpane
  2. always: scrollbars created and always shown by the scrollpane
  3. never: scrollbars never created or shown by the scrollpane

The state of the horizontal and vertical scrollbars is represented by two ScrollPaneAdjustable objects (one for each dimension) which implement the Adjustable interface. The API provides methods to access those objects such that the attributes on the Adjustable object (such as unitIncrement, value, etc.) can be manipulated.

Certain adjustable properties (minimum, maximum, blockIncrement, and visibleAmount) are set internally by the scrollpane in accordance with the geometry of the scrollpane and its child and these should not be set by programs using the scrollpane.

If the scrollbar display policy is defined as "never", then the scrollpane can still be programmatically scrolled using the setScrollPosition() method and the scrollpane will move and clip the child's contents appropriately. This policy is useful if the program needs to create and manage its own adjustable controls.

The placement of the scrollbars is controlled by platform-specific properties set by the user outside of the program.

The initial size of this container is set to 100x100, but can be reset using setSize().

Scrolling with the wheel on a wheel-equipped mouse is enabled by default. This can be disabled using setWheelScrollingEnabled. Wheel scrolling can be customized by setting the block and unit increment of the horizontal and vertical Adjustables. For information on how mouse wheel events are dispatched, see the class description for MouseWheelEvent.

Insets are used to define any space used by scrollbars and any borders created by the scroll pane. getInsets() can be used to get the current value for the insets. If the value of scrollbarsAlwaysVisible is false, then the value of the insets will change dynamically depending on whether the scrollbars are currently visible or not.

See Also:
Serialized Form

  • Field Details

    • SCROLLBARS_AS_NEEDED

      public static final int SCROLLBARS_AS_NEEDED
      Specifies that horizontal/vertical scrollbar should be shown only when the size of the child exceeds the size of the scrollpane in the horizontal/vertical dimension.
      See Also:
      Constant Field Values

    • SCROLLBARS_ALWAYS

      public static final int SCROLLBARS_ALWAYS
      Specifies that horizontal/vertical scrollbars should always be shown regardless of the respective sizes of the scrollpane and child.
      See Also:
      Constant Field Values

    • SCROLLBARS_NEVER

      public static final int SCROLLBARS_NEVER
      Specifies that horizontal/vertical scrollbars should never be shown regardless of the respective sizes of the scrollpane and child.
      See Also:
      Constant Field Values

  • Constructor Details

  • Method Details

    • addImpl

      protected final void addImpl​(Component comp, Object constraints, int index)
      Adds the specified component to this scroll pane container. If the scroll pane has an existing child component, that component is removed and the new one is added.
      Overrides:
      addImpl in class Container
      Parameters:
      comp - the component to be added
      constraints - not applicable
      index - position of child component (must be <= 0)
      See Also:
      Container.add(Component), Container.add(Component, int), Container.add(Component, java.lang.Object), Container.invalidate(), LayoutManager, LayoutManager2

    • getScrollbarDisplayPolicy

      public int getScrollbarDisplayPolicy()
      Returns the display policy for the scrollbars.
      Returns:
      the display policy for the scrollbars

    • getViewportSize

      public Dimension getViewportSize()
      Returns the current size of the scroll pane's view port.
      Returns:
      the size of the view port in pixels

    • getHScrollbarHeight

      public int getHScrollbarHeight()
      Returns the height that would be occupied by a horizontal scrollbar, which is independent of whether it is currently displayed by the scroll pane or not.
      Returns:
      the height of a horizontal scrollbar in pixels

    • getVScrollbarWidth

      public int getVScrollbarWidth()
      Returns the width that would be occupied by a vertical scrollbar, which is independent of whether it is currently displayed by the scroll pane or not.
      Returns:
      the width of a vertical scrollbar in pixels

    • getVAdjustable

      public Adjustable getVAdjustable()
      Returns the ScrollPaneAdjustable object which represents the state of the vertical scrollbar. The declared return type of this method is Adjustable to maintain backward compatibility.
      Returns:
      the vertical scrollbar state
      See Also:
      ScrollPaneAdjustable

    • getHAdjustable

      public Adjustable getHAdjustable()
      Returns the ScrollPaneAdjustable object which represents the state of the horizontal scrollbar. The declared return type of this method is Adjustable to maintain backward compatibility.
      Returns:
      the horizontal scrollbar state
      See Also:
      ScrollPaneAdjustable

    • setScrollPosition

      public void setScrollPosition​(int x, int y)
      Scrolls to the specified position within the child component. A call to this method is only valid if the scroll pane contains a child. Specifying a position outside of the legal scrolling bounds of the child will scroll to the closest legal position. Legal bounds are defined to be the rectangle: x = 0, y = 0, width = (child width - view port width), height = (child height - view port height). This is a convenience method which interfaces with the Adjustable objects which represent the state of the scrollbars.
      Parameters:
      x - the x position to scroll to
      y - the y position to scroll to
      Throws:
      NullPointerException - if the scrollpane does not contain a child

    • setScrollPosition

      public void setScrollPosition​(Point p)
      Scrolls to the specified position within the child component. A call to this method is only valid if the scroll pane contains a child and the specified position is within legal scrolling bounds of the child. Specifying a position outside of the legal scrolling bounds of the child will scroll to the closest legal position. Legal bounds are defined to be the rectangle: x = 0, y = 0, width = (child width - view port width), height = (child height - view port height). This is a convenience method which interfaces with the Adjustable objects which represent the state of the scrollbars.
      Parameters:
      p - the Point representing the position to scroll to
      Throws:
      NullPointerException - if p is null

    • getScrollPosition

      public Point getScrollPosition()
      Returns the current x,y position within the child which is displayed at the 0,0 location of the scrolled panel's view port. This is a convenience method which interfaces with the adjustable objects which represent the state of the scrollbars.
      Returns:
      the coordinate position for the current scroll position
      Throws:
      NullPointerException - if the scrollpane does not contain a child

    • setLayout

      public final void setLayout​(LayoutManager mgr)
      Sets the layout manager for this container. This method is overridden to prevent the layout mgr from being set.
      Overrides:
      setLayout in class Container
      Parameters:
      mgr - the specified layout manager
      See Also:
      Container.doLayout(), Container.getLayout(), Container.invalidate()

    • doLayout

      public void doLayout()
      Lays out this container by resizing its child to its preferred size. If the new preferred size of the child causes the current scroll position to be invalid, the scroll position is set to the closest valid position.
      Overrides:
      doLayout in class Container
      See Also:
      Component.validate()

    • layout

      @Deprecated public void layout()
      Deprecated.
      As of JDK version 1.1, replaced by doLayout().
      Overrides:
      layout in class Container

    • printComponents

      public void printComponents​(Graphics g)
      Prints the component in this scroll pane.
      Overrides:
      printComponents in class Container
      Parameters:
      g - the specified Graphics window
      See Also:
      Component.print(java.awt.Graphics), Component.printAll(java.awt.Graphics)

    • addNotify

      public void addNotify()
      Creates the scroll pane's peer.
      Overrides:
      addNotify in class Container
      See Also:
      Component.isDisplayable(), Container.removeNotify()

    • paramString

      public String paramString()
      Returns a string representing the state of this ScrollPane. 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 Container
      Returns:
      the parameter string of this scroll pane

    • processMouseWheelEvent

      protected void processMouseWheelEvent​(MouseWheelEvent e)
      Process mouse wheel events that are delivered to this ScrollPane by scrolling an appropriate amount.

      Note that if the event parameter is null the behavior is unspecified and may result in an exception.

      Overrides:
      processMouseWheelEvent in class Component
      Parameters:
      e - the mouse wheel event
      Since:
      1.4
      See Also:
      MouseWheelEvent, MouseWheelListener, Component.addMouseWheelListener(java.awt.event.MouseWheelListener), Component.enableEvents(long)

    • eventTypeEnabled

      protected boolean eventTypeEnabled​(int type)
      If wheel scrolling is enabled, we return true for MouseWheelEvents
      Since:
      1.4

    • setWheelScrollingEnabled

      public void setWheelScrollingEnabled​(boolean handleWheel)
      Enables/disables scrolling in response to movement of the mouse wheel. Wheel scrolling is enabled by default.
      Parameters:
      handleWheel - true if scrolling should be done automatically for a MouseWheelEvent, false otherwise.
      Since:
      1.4
      See Also:
      isWheelScrollingEnabled(), MouseWheelEvent, MouseWheelListener

    • isWheelScrollingEnabled

      public boolean isWheelScrollingEnabled()
      Indicates whether or not scrolling will take place in response to the mouse wheel. Wheel scrolling is enabled by default.
      Returns:
      true if the wheel scrolling enabled; otherwise false
      Since:
      1.4
      See Also:
      setWheelScrollingEnabled(boolean)

    • getAccessibleContext

      public AccessibleContext getAccessibleContext()
      Gets the AccessibleContext associated with this ScrollPane. For scroll panes, the AccessibleContext takes the form of an AccessibleAWTScrollPane. A new AccessibleAWTScrollPane instance is created if necessary.
      Specified by:
      getAccessibleContext in interface Accessible
      Overrides:
      getAccessibleContext in class Component
      Returns:
      an AccessibleAWTScrollPane that serves as the AccessibleContext of this ScrollPane
      Since:
      1.3