[Chapter 19] ScrollPane
Author: John Zukowski
Date: Thu Jul 31 15:15:53 1997

#

| Chapter 19 java.awt Reference |

# ScrollPane

## Name

ScrollPane

##

## Description

The `ScrollPane` class provides automatic scrolling of a child component.

## Class Definition

    public class java.awt.ScrollPane
        extends java.awt.Container {
      // Constants
      public final static int SCROLLBARS_ALWAYS;
      public final static int SCROLLBARS_AS_NEEDED;
      public final static int SCROLLBARS_NEVER;
      // Constructors
      public ScrollPane();
      public ScrollPane (int scrollbarDisplayPolicy);
      // Public Instance Methods
      public void addNotify();
      public void doLayout();
      public Adjustable getHAdjustable();
      public int getHScrollbarHeight();
      public Point getScrollPosition();
      public int getScrollbarDisplayPolicy();
      public Adjustable getVAdjustable();
      public int getVScrollbarWidth();
      public Dimension getViewportSize();
      public void layout();
      public String paramString();
      public void printComponents (Graphics g);
      public final void setLayout (LayoutManager mgr);
      public void setScrollPosition (int x, int y);
      public void setScrollPosition (Point p);

      //Protected Instance Methods
      protected final void addImpl (Component comp, Object constraints,
        int index);
    }

## Constants

### SCROLLBARS_ALWAYS

#### public final static int SCROLLBARS_ALWAYS

Always show the scrollbars.

### SCROLLBARS_AS_NEEDED

#### public final static int SCROLLBARS_AS_NEEDED

Only show the scrollbars if the contents of the `ScrollPane` are larger than what is visible.

### SCROLLBARS_NEVER

#### public final static int SCROLLBARS_NEVER

Don't ever show the scrollbars. The `ScrollPane` can still be scrolled programmatically.

## Constructors

### ScrollPane

#### public ScrollPane()

Description

  Constructs a `ScrollPane` object with `SCROLLBARS_AS_NEEDED`.

#### public ScrollPane (int scrollbarDisplayPolicy)

Parameters

  scrollbarDisplayPolicy

    One of the `SCROLLBARS_` constants.

Description

  Constructs a `ScrollPane` object with the specified scrollbar display policy.

## Instance Methods

### addImpl

#### protected final void addImpl (Component comp, Object constraints, int index)

Parameters

  comp

    The component to add to the `Scrollpane`.

  constraints

    Layout constraints; ignored.

  index

    The position at which to add the component; should always be less than or equal to 0.

Returns

  The component that was added.

Overrides

  `Container.addImpl (Component, Object, int)`

Throws

  IllegalArgumentException

    If `pos` is greater than 0.

Description

  Adds a child component to the `Scrollpane`. If there already was a child component, it is replaced by the new component.

### addNotify

#### public void addNotify()

Overrides

  `Container.addNotify()`

Description

  Creates `ScrollPane`'s peer.

### doLayout

#### public void doLayout()

Overrides

  `Container.doLayout()`

Description

  Lays out the `ScrollPane`. Resizes the child component to its preferred size.

### getHAdjustable

#### public Adjustable getHAdjustable()

Returns

  The object implementing the `Adjustable` interface that is used to adjust the `ScrollPane` horizontally. Usually this is a `Scrollbar`.

### getHScrollbarHeight

#### public int getHScrollbarHeight()

Returns

  The height a horizontal scrollbar would occupy, regardless of whether it's shown or not.

### getScrollPosition

#### public Point getScrollPosition()

Returns

  Returns the position within the child component that is displayed at 0, 0 in the `ScrollPane`.

### getScrollbarDisplayPolicy

#### public int getScrollbarDisplayPolicy()

Returns

  The display policy for the scrollbars (one of the `SCROLLBARS_` constants).

### getVAdjustable

#### public Adjustable getVAdjustable()

Returns

  The object implementing the `Adjustable` interface that is used to adjust the `ScrollPane` vertically. Usually this is a `Scrollbar`.

### getVScrollbarWidth

#### public int getVScrollbarWidth()

Returns

  The width a vertical scrollbar would occupy, regardless of whether it's shown or not.

### getViewportSize

#### public Dimension getViewportSize()

Returns

  The size of the `ScrollPane`'s port (the area of the child component that is shown).

### layout

#### public void layout()

Overrides

  `Container.layout()`

Description

  Lays out component. Replaced by `doLayout()`.

### paramString

#### public String paramString()

Returns

  String with current settings of `ScrollPane`.

Overrides

  `Container.paramString()`

Description

  Helper method for `toString()` to generate string of current settings.

### printComponents

#### public void printComponents (Graphics g)

Parameters

  g

    Graphics context.

Overrides

  `Container.printComponents(Graphics)`

Description

  Prints the `ScrollPane`'s child component.

### setLayout

#### public void setLayout (LayoutManager manager)

Parameters

  manager

    Ignored.

Overrides

  `Container.setLayout(LayoutManager)`

Description

  Does nothing. No layout manager is needed because there is only one child component.

### setScrollPosition

#### public void setScrollPosition (int x, int y)

Parameters

  x

    New horizontal position.

  y

    New vertical position.

Throws

  IllegalArgumentException

    If the point given is not valid.

Description

  Scroll to the given position in the child component.

#### public void setScrollPosition (Point p)

Parameters

  p

    New position.

Throws

  IllegalArgumentException

    If the point given is not valid.

Description

  Scroll to the given position in the child component.

## See Also

`Adjustable`, `Container`, `Point`, `Scrollbar`

Rectangle |  | Scrollbar