LayoutFocusTraversalPolicy (Java Platform SE 8 )
Keywords: javax.swing.LayoutFocusTraversalPolicy class
Date: 2015-05-24

javax.swing

## Class LayoutFocusTraversalPolicy

- java.lang.Object
- - java.awt.FocusTraversalPolicy
  - - javax.swing.InternalFrameFocusTraversalPolicy
    - - javax.swing.SortingFocusTraversalPolicy
      - - javax.swing.LayoutFocusTraversalPolicy

- All Implemented Interfaces:
    Serializable

      public class LayoutFocusTraversalPolicy
      extends SortingFocusTraversalPolicy
      implements Serializable

  A SortingFocusTraversalPolicy which sorts Components based on their size, position, and orientation. Based on their size and position, Components are roughly categorized into rows and columns. For a Container with horizontal orientation, columns run left-to-right or right-to-left, and rows run top- to-bottom. For a Container with vertical orientation, columns run top-to- bottom and rows run left-to-right or right-to-left. See `ComponentOrientation` for more information. All columns in a row are fully traversed before proceeding to the next row.
  Since:
    1.4
  See Also:
    `ComponentOrientation`

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `LayoutFocusTraversalPolicy()` Constructs a LayoutFocusTraversalPolicy.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected boolean` | `accept(Component aComponent)` Determines whether the specified `Component` is an acceptable choice as the new focus owner.
    `Component` | `getComponentAfter(Container aContainer, Component aComponent)` Returns the Component that should receive the focus after aComponent.
    `Component` | `getComponentBefore(Container aContainer, Component aComponent)` Returns the Component that should receive the focus before aComponent.
    `Component` | `getFirstComponent(Container aContainer)` Returns the first Component in the traversal cycle.
    `Component` | `getLastComponent(Container aContainer)` Returns the last Component in the traversal cycle.

    - ### Methods inherited from class javax.swing.SortingFocusTraversalPolicy

      `getComparator, getDefaultComponent, getImplicitDownCycleTraversal, setComparator, setImplicitDownCycleTraversal`

    - ### Methods inherited from class javax.swing.InternalFrameFocusTraversalPolicy

      `getInitialComponent`

    - ### Methods inherited from class java.awt.FocusTraversalPolicy

      `getInitialComponent`

    - ### Methods inherited from class java.lang.Object

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

- - ### Constructor Detail

    - #### LayoutFocusTraversalPolicy

          public LayoutFocusTraversalPolicy()

      Constructs a LayoutFocusTraversalPolicy.

  - ### Method Detail

    - #### getComponentAfter

          public Component getComponentAfter(Container aContainer,
                                             Component aComponent)

      Returns the Component that should receive the focus after aComponent. aContainer must be a focus cycle root of aComponent.

      By default, LayoutFocusTraversalPolicy implicitly transfers focus down- cycle. That is, during normal focus traversal, the Component traversed after a focus cycle root will be the focus-cycle-root's default Component to focus. This behavior can be disabled using the `setImplicitDownCycleTraversal` method.

      If aContainer is focus traversal policy provider, the focus is always transferred down-cycle.

      Overrides:
        `getComponentAfter` in class `SortingFocusTraversalPolicy`
      Parameters:
        `aContainer` - a focus cycle root of aComponent or a focus traversal policy provider
        `aComponent` - a (possibly indirect) child of aContainer, or aContainer itself
      Returns:
        the Component that should receive the focus after aComponent, or null if no suitable Component can be found
      Throws:
        `IllegalArgumentException` - if aContainer is not a focus cycle root of aComponent or a focus traversal policy provider, or if either aContainer or aComponent is null

    - #### getComponentBefore

          public Component getComponentBefore(Container aContainer,
                                              Component aComponent)

      Returns the Component that should receive the focus before aComponent. aContainer must be a focus cycle root of aComponent.

      By default, LayoutFocusTraversalPolicy implicitly transfers focus down- cycle. That is, during normal focus traversal, the Component traversed after a focus cycle root will be the focus-cycle-root's default Component to focus. This behavior can be disabled using the `setImplicitDownCycleTraversal` method.

      If aContainer is focus traversal policy provider, the focus is always transferred down-cycle.

      Overrides:
        `getComponentBefore` in class `SortingFocusTraversalPolicy`
      Parameters:
        `aContainer` - a focus cycle root of aComponent or a focus traversal policy provider
        `aComponent` - a (possibly indirect) child of aContainer, or aContainer itself
      Returns:
        the Component that should receive the focus before aComponent, or null if no suitable Component can be found
      Throws:
        `IllegalArgumentException` - if aContainer is not a focus cycle root of aComponent or a focus traversal policy provider, or if either aContainer or aComponent is null

    - #### getFirstComponent

          public Component getFirstComponent(Container aContainer)

      Returns the first Component in the traversal cycle. This method is used to determine the next Component to focus when traversal wraps in the forward direction.
      Overrides:
        `getFirstComponent` in class `SortingFocusTraversalPolicy`
      Parameters:
        `aContainer` - a focus cycle root of aComponent or a focus traversal policy provider whose first Component is to be returned
      Returns:
        the first Component in the traversal cycle of aContainer, or null if no suitable Component can be found
      Throws:
        `IllegalArgumentException` - if aContainer is null

    - #### getLastComponent

          public Component getLastComponent(Container aContainer)

      Returns the last Component in the traversal cycle. This method is used to determine the next Component to focus when traversal wraps in the reverse direction.
      Overrides:
        `getLastComponent` in class `SortingFocusTraversalPolicy`
      Parameters:
        `aContainer` - a focus cycle root of aComponent or a focus traversal policy provider whose last Component is to be returned
      Returns:
        the last Component in the traversal cycle of aContainer, or null if no suitable Component can be found
      Throws:
        `IllegalArgumentException` - if aContainer is null

    - #### accept

          protected boolean accept(Component aComponent)

      Determines whether the specified `Component` is an acceptable choice as the new focus owner. This method performs the following sequence of operations:
      1. Checks whether `aComponent` is visible, displayable, enabled, and focusable. If any of these properties is `false`, this method returns `false`.
      2. If `aComponent` is an instance of `JTable`, returns `true`.
      3. If `aComponent` is an instance of `JComboBox`, then returns the value of `aComponent.getUI().isFocusTraversable(aComponent)`.
      4. If `aComponent` is a `JComponent` with a `JComponent.WHEN_FOCUSED` `InputMap` that is neither `null` nor empty, returns `true`.
      5. Returns the value of `DefaultFocusTraversalPolicy.accept(aComponent)`.
      Overrides:
        `accept` in class `SortingFocusTraversalPolicy`
      Parameters:
        `aComponent` - the `Component` whose fitness as a focus owner is to be tested
      Returns:
        `true` if `aComponent` is a valid choice for a focus owner; otherwise `false`
      See Also:
        `Component.isVisible()`, `Component.isDisplayable()`, `Component.isEnabled()`, `Component.isFocusable()`, `ComboBoxUI.isFocusTraversable(javax.swing.JComboBox)`, `JComponent.getInputMap(int)`, `DefaultFocusTraversalPolicy.accept(java.awt.Component)`

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