[Chapter 19] Container

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| Chapter 19 java.awt Reference |

# Container

## Name

Container

##

## Description

The `Container` class serves as a general purpose holder of other `Component` objects.

## Class Definition

    public abstract class java.awt.Container
        extends java.awt.Component {
      // Constructors
      protected Container();

      // Instance Methods
      public Component add (Component component);
      public Component add (Component component, int position);
      public void add (Component comp, Object constraints);
      public void add (Component comp, Object constraints,
          int position);
      public Component add (String name, Component component);
      public void addContainerListener (ContainerListener l);
      public void addNotify();
      public int countComponents();
      public void deliverEvent (Event e);
      public void doLayout();
      public float getAlignmentX();
      public float getAlignmentY();
      public Component getComponent (int n);
      public Component getComponentAt (int x, int y);
      public Component getComponentAt (Point p);
      public int getComponentCount();
      public Component[] getComponents();
      public Insets getInsets();
      public LayoutManager getLayout();
      public Dimension getMaximumSize();
      public Dimension getMinimumSize();
      public Dimension getPreferredSize();
      public Insets insets();
      public void invalidate();
      public boolean isAncestorOf (Component c);
      public void layout();
      public void list (PrintStream out, int indentation);
      public void list (PrintWriter out, int indentation);
      public Component locate (int x, int y);
      public Dimension minimumSize();
      public void paint (Graphics g);
      public void paintComponents (Graphics g);
      public Dimension preferredSize();
      public void print (Graphics g);
      public void printComponents (Graphics g);
      public void remove (int index);
      public void remove (Component component);
      public void removeAll();
      public void removeContainerListener (ContainerListener l);
      public void removeNotify();
      public void setLayout (LayoutManager manager);
      public void validate();
      // Protected Instance Methods
      protected void addImpl (Component comp, Object constraints,
          int index);
      protected String paramString();
      protected void processContainerEvent (ContainerEvent e);
      protected void processEvent (AWTEvent e);
      protected void validateTree();
    }

## Constructors

### Container

#### protected Container()

Description

  This constructor creates a "lightweight" container. This constructor allows `Container` to be subclassed using code written entirely in Java.

## Instance Methods

### add

#### public Component add (Component component)

Parameters

  component

    `Component` to add to container.

Returns

  `Component` just added.

Throws

  `IllegalArgumentException` if you add `component` to itself.

Description

  Adds `component` as the last component in the container.

#### public Component add (Component component, int position)

Parameters

  component

    `Component` to add to container.

  position

    Position of component; -1 adds the component as the last in the container.

Returns

  `Component just added.`

Throws

  `ArrayIndexOutOfBoundsException`

    If `position` invalid.

  `IllegalArgumentException`

    If you add `Component` to itself.

Description

  Adds `component` to container at a certain position.

#### public void add (Component component, Object constraints)

Parameters

  component

    `Component` to add to container.

  constraints

    An object describing constraints on the component being added.

Description

  Adds `component` to container subject to `contraints`.

#### public void add (Component component, Object constraints, int index)

Parameters

  component

    `Component` to add to container.

  constraints

    An object describing constraints on the component being added.

  index

    The position of the component in the container's list.

Description

  Adds `component` to container subject to `contraints` at position `index`.

#### public Component add (String name, Component component)

Parameters

  name

    Name of component being added. This parameter is often significant to the layout manager of the container (e.g "North", "Center").

  component

    `Component` to add to container.

Returns

  `Component` just added.

Throws

  IllegalArgumentException

    If you add `component` to itself.

Description

  Adds the component to the container with the given `name`. Replaced by the more general `add(Component, Object)`.

### addContainerListener

#### public void addContainerListener (ContainerListener l)

Parameters

  l

    An object that implements the `ContainerListener` interface.

Description

  Add a listener for the container events.

### addNotify

#### public void addNotify()

Overrides

  `Component.addNotify()`

Description

  Creates `Container`'s peer and peers of contained components.

### countComponents

#### public int countComponents()

Returns

  Number of components within `Container`.

### deliverEvent

#### public void deliverEvent (Event e)

Parameters

  e

    `Event` instance to deliver.

Overrides

  `Component.deliverEvent(Event)`

Description

  Tries to locate the component contained in the container that should receive the event.

### doLayout

#### public void doLayout()

Description

  Lays out the container. This method is a replacement for `layout()`.

### getAlignmentX

#### public float getAlignmentX()

Returns

  A number between 0 and 1 representing the horizontal alignment of this component.

Overrides

  `Component.getAlignmentX()`

Description

  If the container's layout manager implements `LayoutManager2`, this method returns the `getLayoutAlignmentX()` value of the layout manager. Otherwise the `getAlignmentX()` value of `Component` is returned.

### getAlignmentY

#### public float getAlignmentY()

Returns

  A number between 0 and 1 representing the vertical alignment of this component.

Overrides

  `Component.getAlignmentY()`

Description

  If the container's layout manager implements `LayoutManager2`, this method returns the `getLayoutAlignmentY()` value of the layout manager. Otherwise the `getAlignmentY()` value of `Component` is returned.

### getComponent

#### public synchronized Component getComponent (int position)

Parameters

  position

    Position of component to get.

Throws

  `ArrayIndexOutOfBoundsException`

    If `position` is invalid.

Returns

  `Component` at designated `position` within `Container`.

### getComponentAt

#### public Component getComponentAt (int x, int y)

Parameters

  x

    The x coordinate, in this `Container`'s coordinate system.

  y

    The y coordinate, in this `Container`'s coordinate system.

Returns

  Returns the `Component` containing the give point.

#### public Component getComponentAt (Point p)

Parameters

  p

    The point to be tested, in this `Container`'s coordinate system.

Returns

  Returns the `Component` containing the give point.

### getComponentCount

#### public int getComponentCount()

Returns

  Returns the number of components in the container.

### getComponents

#### public Component[] getComponents()

Returns

  Array of components within the container.

### getInsets

#### public Insets getInsets()

Returns

  The insets of the container.

### getLayout

#### public LayoutManager getLayout()

Returns

  `LayoutManager` of `Container`.

### getMaximumSize

#### public Dimension getMaximumSize()

Overrides

  `Component.getMaximumSize()`

Returns

  The maximum dimensions of the component.

### getMinimumSize

#### public Dimension getMinimumSize()

Overrides

  `Component.getMinimumSize()`

Returns

  The minimum dimensions of the component.

### getPreferredSize

#### public Dimension getPreferredSize()

Returns

  The preferred dimensions of the component.

### insets

#### public Insets insets()

Returns

  Current `Insets` of `Container`. Replaced by `getInsets()`.

### invalidate

#### public void invalidate()

Overrides

  `Component.invalidate()`

Description

  Sets the container's valid state to `false`.

### isAncestorOf

#### public boolean isAncestorOf (Component c)

Parameters

  c

    The component in question.

Returns

  If `c` is contained in the container's hierarchy, returns `true`; otherwise `false`.

### layout

#### public void layout()

Overrides

  `Component.layout()`

Description

  Replaced by `doLayout()`.

### list

#### public void list (PrintStream out, int indentation)

Parameters

  out

    Output `Stream` to send results to.

  indentation

    Indentation to use when printing.

Overrides

  `Component.list(PrintStream, int)`

Description

  Recursively lists all components in `Container`.

#### public void list (PrintWriter out, int indentation)

Parameters

  out

    Output `Writer` to send results to.

  indentation

    Indentation to use when printing.

Overrides

  `Component.list(PrintWriter, int)`

Description

  Recursively lists all components in `Container`.

### locate

#### public Component locate (int x, int y)

Parameters

  x

    Horizontal position to check.

  y

    Vertical position to check.

Returns

  `Component` within `Container` at given coordinates, or `Container`.

Overrides

  `Component.locate(int, int)`

Description

  Replaced by `getComponentAt(int, int)`.

### minimizeSize

#### public Dimension minimumSize()

Returns

  Minimum dimensions of contained objects.

Overrides

  `Component.minimumSize()`

Description

  Replaced by `getMinimumSize()`.

### paint

#### public void paint (Graphics g)

Parameters

  g

    Graphics context of container.

Overrides

  `Component.paint()`

Description

  This method tells any lightweight components that are children of this container to paint themselves.

### paintComponents

#### public void paintComponents (Graphics g)

Parameters

  g

    Graphics context of `Container`.

Description

  Paints the different components in `Container`.

### preferredSize

#### public Dimension preferredSize()

Returns

  Preferred dimensions of contained objects.

Overrides

  `Component.preferredSize()`

Description

  Replaced by `getPreferredSize()`.

### print

#### public void print (Graphics g)

Parameters

  g

    Graphics context of container.

Overrides

  `Component.print()`

Description

  This method tells any lightweight components that are children of this container to print themselves.

### printComponents

#### public void printComponents (Graphics g)

Parameters

  g

    Graphics context of `Container`.

Description

  Prints the different components in `Container`.

### remove

#### public void remove (int index)

Parameters

  index

    Index of the component to remove.

Description

  Removes the component in position `index` from `Container`.

#### public void remove (Component component)

Parameters

  component

    `Component` to remove.

Description

  Removes `component` from `Container`.

### removeAll

#### public void removeAll()

Description

  Removes all components from `Container`.

### removeContainerListener

#### public void removeContainerListener (ContainerListener l)

Parameters

  l

    One of this `Container`'s `ContainerListener`s.

Description

  Remove a container event listener.

### removeNotify

#### public void removeNotify()

Overrides

  `Component.removeNotify()`

Description

  Removes `Container`'s peer and peers of contained components.

### setLayout

#### public void setLayout (LayoutManager manager)

Parameters

  manager

    New `LayoutManager` for `Container`.

Description

  Changes `LayoutManager` of `Container`.

### validate

#### public void validate()

Overrides

  `Component.validate()`

Description

  Sets `Container`'s valid state to `true` and recursively validates its children.

## Protected Instance Methods

### addImpl

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

Parameters

  comp

    The component to add.

  constraints

    Constraints on the component.

  index

    Position at which to add this component. Pass -1 to add the component at the end.

Description

  This method adds a component subject to the given constraints at a specific position in the container's list of components. It is a helper method for the various overrides of `add()`.

### paramString

#### protected String paramString()

Returns

  String with current settings of `Container`.

Overrides

  `Component.paramString()`

Description

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

### processContainerEvent

#### protected void processContainerEvent (ContainerEvent e)

Parameters

  e

    The event to process.

Description

  Container events are passed to this method for processing. Normally, this method is called by `processEvent()`.

### processEvent

#### protected void processEvent (AWTEvent e)

Parameters

  e

    The event to process.

Overrides

  `Component.processEvent()`

Description

  Low level `AWTEvent`s are passed to this method for processing.

### validateTree

#### protected void validateTree()

Description

  Descends recursively into the `Container`'s components and recalculates layout for any subtrees that are marked invalid.

## See Also

`Component`, `Dimension`, `Event`, `Graphics`, `Insets`, `LayoutManager`, `Panel`, `PrintStream`, `String`, `Window`

Component |  | Cursor