# 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

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `protected class`
  `ScrollPane.AccessibleAWTScrollPane`
  This class implements accessibility support for the `ScrollPane` class.

  ### Nested classes/interfaces declared in class Container

  `Container.AccessibleAWTContainer`

  ### Nested classes/interfaces declared in class Component

  `Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy`

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final int`
  `SCROLLBARS_ALWAYS`
  Specifies that horizontal/vertical scrollbars should always be shown regardless of the respective sizes of the scrollpane and child.
  `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.
  `static final int`
  `SCROLLBARS_NEVER`
  Specifies that horizontal/vertical scrollbars should never be shown regardless of the respective sizes of the scrollpane and child.

  ### Fields declared in class Component

  `accessibleContext, BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT`

  ### Fields declared in interface ImageObserver

  `ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `ScrollPane()`
  Create a new scrollpane container with a scrollbar display policy of "as needed".
  `ScrollPane(int scrollbarDisplayPolicy)`
  Create a new scrollpane container.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected final void`
  `addImpl(Component comp, Object constraints, int index)`
  Adds the specified component to this scroll pane container.
  `void`
  `addNotify()`
  Creates the scroll pane's peer.
  `void`
  `doLayout()`
  Lays out this container by resizing its child to its preferred size.
  `protected boolean`
  `eventTypeEnabled(int type)`
  If wheel scrolling is enabled, we return true for MouseWheelEvents
  `AccessibleContext`
  `getAccessibleContext()`
  Gets the AccessibleContext associated with this ScrollPane.
  `Adjustable`
  `getHAdjustable()`
  Returns the `ScrollPaneAdjustable` object which represents the state of the horizontal scrollbar.
  `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.
  `int`
  `getScrollbarDisplayPolicy()`
  Returns the display policy for the scrollbars.
  `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.
  `Adjustable`
  `getVAdjustable()`
  Returns the `ScrollPaneAdjustable` object which represents the state of the vertical scrollbar.
  `Dimension`
  `getViewportSize()`
  Returns the current size of the scroll pane's view port.
  `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.
  `boolean`
  `isWheelScrollingEnabled()`
  Indicates whether or not scrolling will take place in response to the mouse wheel.
  `void`
  `layout()`
  Deprecated.
  As of JDK version 1.1, replaced by `doLayout()`.
  `String`
  `paramString()`
  Returns a string representing the state of this `ScrollPane`.
  `void`
  `printComponents(Graphics g)`
  Prints the component in this scroll pane.
  `protected void`
  `processMouseWheelEvent(MouseWheelEvent e)`
  Process mouse wheel events that are delivered to this `ScrollPane` by scrolling an appropriate amount.
  `final void`
  `setLayout(LayoutManager mgr)`
  Sets the layout manager for this container.
  `void`
  `setScrollPosition(int x, int y)`
  Scrolls to the specified position within the child component.
  `void`
  `setScrollPosition(Point p)`
  Scrolls to the specified position within the child component.
  `void`
  `setWheelScrollingEnabled(boolean handleWheel)`
  Enables/disables scrolling in response to movement of the mouse wheel.

  ### Methods declared in class Container

  `add, add, add, add, add, addContainerListener, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, countComponents, deliverEvent, findComponentAt, findComponentAt, getAlignmentX, getAlignmentY, getComponent, getComponentAt, getComponentAt, getComponentCount, getComponents, getComponentZOrder, getContainerListeners, getFocusTraversalKeys, getFocusTraversalPolicy, getInsets, getLayout, getListeners, getMaximumSize, getMinimumSize, getMousePosition, getPreferredSize, insets, invalidate, isAncestorOf, isFocusCycleRoot, isFocusCycleRoot, isFocusTraversalPolicyProvider, isFocusTraversalPolicySet, isValidateRoot, list, list, locate, minimumSize, paint, paintComponents, preferredSize, print, processContainerEvent, processEvent, remove, remove, removeAll, removeContainerListener, removeNotify, setComponentZOrder, setFocusCycleRoot, setFocusTraversalKeys, setFocusTraversalPolicy, setFocusTraversalPolicyProvider, setFont, transferFocusDownCycle, update, validate, validateTree`

  ### Methods declared in class Component

  `action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, createVolatileImage, createVolatileImage, disable, disableEvents, dispatchEvent, enable, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getBackground, getBaseline, getBaselineResizeBehavior, getBounds, getBounds, getColorModel, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeysEnabled, getFont, getFontMetrics, getForeground, getGraphics, getGraphicsConfiguration, getHeight, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getLocale, getLocation, getLocation, getLocationOnScreen, getMouseListeners, getMouseMotionListeners, getMousePosition, getMouseWheelListeners, getName, getParent, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getSize, getToolkit, getTreeLock, getWidth, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, isBackgroundSet, isCursorSet, isDisplayable, isDoubleBuffered, isEnabled, isFocusable, isFocusOwner, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isOpaque, isPreferredSizeSet, isShowing, isValid, isVisible, keyDown, keyUp, list, list, list, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, postEvent, prepareImage, prepareImage, printAll, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, requestFocus, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, requestFocusInWindow, reshape, resize, resize, revalidate, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeysEnabled, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setMixingCutoutShape, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle`

  ### Methods declared in class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- ## 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

  - ### ScrollPane

    public ScrollPane() throws HeadlessException
    Create a new scrollpane container with a scrollbar display policy of "as needed".
    Throws:
      `HeadlessException` - if GraphicsEnvironment.isHeadless() returns true
    See Also:
      - `GraphicsEnvironment.isHeadless()`

  - ### ScrollPane

    @ConstructorProperties("scrollbarDisplayPolicy") public ScrollPane(int scrollbarDisplayPolicy) throws HeadlessException
    Create a new scrollpane container.
    Parameters:
      `scrollbarDisplayPolicy` - policy for when scrollbars should be shown
    Throws:
      `IllegalArgumentException` - if the specified scrollbar display policy is invalid
      `HeadlessException` - if GraphicsEnvironment.isHeadless() returns true
    See Also:
      - `GraphicsEnvironment.isHeadless()`

- ## 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(Graphics)`
      - `Component.printAll(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(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