IT. Expert System.

Java Standard Edition (SE)

Choice


java.awt

Class Choice

  • All Implemented Interfaces:
    ImageObserver, ItemSelectable, MenuContainer, Serializable, Accessible


    public class Choice
    extends Component
    implements ItemSelectable, Accessible
    The Choice class presents a pop-up menu of choices. The current choice is displayed as the title of the menu.

    The following code example produces a pop-up menu:


     Choice ColorChooser = new Choice();
     ColorChooser.add("Green");
     ColorChooser.add("Red");
     ColorChooser.add("Blue");
     

    After this choice menu has been added to a panel, it appears as follows in its normal state:

    the following text describes the graphic

    In the picture, "Green" is the current choice. Pushing the mouse button down on the object causes a menu to appear with the current choice highlighted.

    Some native platforms do not support arbitrary resizing of Choice components and the behavior of setSize()/getSize() is bound by such limitations. Native GUI Choice components' size are often bound by such attributes as font size and length of items contained within the Choice.

    Since:
    JDK1.0
    See Also:
    Serialized Form
    • Method Detail

      • getItemCount

        public int getItemCount()
        Returns the number of items in this Choice menu.
        Returns:
        the number of items in this Choice menu
        Since:
        JDK1.1
        See Also:
        getItem(int)
      • countItems

        @Deprecated
        public int countItems()
        Deprecated. As of JDK version 1.1, replaced by getItemCount().
      • getItem

        public String getItem(int index)
        Gets the string at the specified index in this Choice menu.
        Parameters:
        index - the index at which to begin
        See Also:
        getItemCount()
      • add

        public void add(String item)
        Adds an item to this Choice menu.
        Parameters:
        item - the item to be added
        Throws:
        NullPointerException - if the item's value is null
        Since:
        JDK1.1
      • addItem

        public void addItem(String item)
        Obsolete as of Java 2 platform v1.1. Please use the add method instead.

        Adds an item to this Choice menu.

        Parameters:
        item - the item to be added
        Throws:
        NullPointerException - if the item's value is equal to null
      • insert

        public void insert(String item,
                           int index)
        Inserts the item into this choice at the specified position. Existing items at an index greater than or equal to index are shifted up by one to accommodate the new item. If index is greater than or equal to the number of items in this choice, item is added to the end of this choice.

        If the item is the first one being added to the choice, then the item becomes selected. Otherwise, if the selected item was one of the items shifted, the first item in the choice becomes the selected item. If the selected item was no among those shifted, it remains the selected item.

        Parameters:
        item - the non-null item to be inserted
        index - the position at which the item should be inserted
        Throws:
        IllegalArgumentException - if index is less than 0
      • remove

        public void remove(String item)
        Removes the first occurrence of item from the Choice menu. If the item being removed is the currently selected item, then the first item in the choice becomes the selected item. Otherwise, the currently selected item remains selected (and the selected index is updated accordingly).
        Parameters:
        item - the item to remove from this Choice menu
        Throws:
        IllegalArgumentException - if the item doesn't exist in the choice menu
        Since:
        JDK1.1
      • remove

        public void remove(int position)
        Removes an item from the choice menu at the specified position. If the item being removed is the currently selected item, then the first item in the choice becomes the selected item. Otherwise, the currently selected item remains selected (and the selected index is updated accordingly).
        Parameters:
        position - the position of the item
        Throws:
        IndexOutOfBoundsException - if the specified position is out of bounds
        Since:
        JDK1.1
      • removeAll

        public void removeAll()
        Removes all items from the choice menu.
        Since:
        JDK1.1
        See Also:
        remove(java.lang.String)
      • getSelectedItem

        public String getSelectedItem()
        Gets a representation of the current choice as a string.
        Returns:
        a string representation of the currently selected item in this choice menu
        See Also:
        getSelectedIndex()
      • getSelectedIndex

        public int getSelectedIndex()
        Returns the index of the currently selected item. If nothing is selected, returns -1.
        Returns:
        the index of the currently selected item, or -1 if nothing is currently selected
        See Also:
        getSelectedItem()
      • select

        public void select(int pos)
        Sets the selected item in this Choice menu to be the item at the specified position.

        Note that this method should be primarily used to initially select an item in this component. Programmatically calling this method will not trigger an ItemEvent. The only way to trigger an ItemEvent is by user interaction.

        Parameters:
        pos - the position of the selected item
        Throws:
        IllegalArgumentException - if the specified position is greater than the number of items or less than zero
        See Also:
        getSelectedItem(), getSelectedIndex()
      • select

        public void select(String str)
        Sets the selected item in this Choice menu to be the item whose name is equal to the specified string. If more than one item matches (is equal to) the specified string, the one with the smallest index is selected.

        Note that this method should be primarily used to initially select an item in this component. Programmatically calling this method will not trigger an ItemEvent. The only way to trigger an ItemEvent is by user interaction.

        Parameters:
        str - the specified string
        See Also:
        getSelectedItem(), getSelectedIndex()
      • getListeners

        public <T extends EventListener> T[] getListeners(Class<T> listenerType)
        Returns an array of all the objects currently registered as FooListeners upon this Choice. FooListeners are registered using the addFooListener method.

        You can specify the listenerType argument with a class literal, such as FooListener.class. For example, you can query a Choice c for its item listeners with the following code:

        ItemListener[] ils = (ItemListener[])(c.getListeners(ItemListener.class));
        If no such listeners exist, this method returns an empty array.
        Overrides:
        getListeners in class Component
        Parameters:
        listenerType - the type of listeners requested; this parameter should specify an interface that descends from java.util.EventListener
        Returns:
        an array of all objects registered as FooListeners on this choice, or an empty array if no such listeners have been added
        Throws:
        ClassCastException - if listenerType doesn't specify a class or interface that implements java.util.EventListener
        Since:
        1.3
        See Also:
        getItemListeners()
      • processEvent

        protected void processEvent(AWTEvent e)
        Processes events on this choice. If the event is an instance of ItemEvent, it invokes the processItemEvent method. Otherwise, it calls its superclass's processEvent method.

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

        Overrides:
        processEvent in class Component
        Parameters:
        e - the event
        Since:
        JDK1.1
        See Also:
        ItemEvent, processItemEvent(java.awt.event.ItemEvent)
      • processItemEvent

        protected void processItemEvent(ItemEvent e)
        Processes item events occurring on this Choice menu by dispatching them to any registered ItemListener objects.

        This method is not called unless item events are enabled for this component. Item events are enabled when one of the following occurs:

        • An ItemListener object is registered via addItemListener.
        • Item events are enabled via enableEvents.

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

        Parameters:
        e - the item event
        Since:
        JDK1.1
        See Also:
        ItemEvent, ItemListener, addItemListener(ItemListener), Component.enableEvents(long)
      • paramString

        protected String paramString()
        Returns a string representing the state of this Choice menu. 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 Component
        Returns:
        the parameter string of this Choice menu
      • getAccessibleContext

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


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