IT. Expert System.

Java Standard Edition (SE)

Checkbox


java.awt

Class Checkbox

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


    public class Checkbox
    extends Component
    implements ItemSelectable, Accessible
    A check box is a graphical component that can be in either an "on" (true) or "off" (false) state. Clicking on a check box changes its state from "on" to "off," or from "off" to "on."

    The following code example creates a set of check boxes in a grid layout:


     setLayout(new GridLayout(3, 1));
     add(new Checkbox("one", null, true));
     add(new Checkbox("two"));
     add(new Checkbox("three"));
     

    This image depicts the check boxes and grid layout created by this code example:

    the following context describes the graphic.

    The button labeled one is in the "on" state, and the other two are in the "off" state. In this example, which uses the GridLayout class, the states of the three check boxes are set independently.

    Alternatively, several check boxes can be grouped together under the control of a single object, using the CheckboxGroup class. In a check box group, at most one button can be in the "on" state at any given time. Clicking on a check box to turn it on forces any other check box in the same group that is on into the "off" state.

    Since:
    JDK1.0
    See Also:
    GridLayout, CheckboxGroup, Serialized Form
    • Constructor Detail

      • Checkbox

        public Checkbox(String label)
                 throws HeadlessException
        Creates a check box with the specified label. The state of this check box is set to "off," and it is not part of any check box group.
        Parameters:
        label - a string label for this check box, or null for no label.
        Throws:
        HeadlessException - if GraphicsEnvironment.isHeadless returns true
        See Also:
        GraphicsEnvironment.isHeadless()
      • Checkbox

        public Checkbox(String label,
                        boolean state)
                 throws HeadlessException
        Creates a check box with the specified label and sets the specified state. This check box is not part of any check box group.
        Parameters:
        label - a string label for this check box, or null for no label
        state - the initial state of this check box
        Throws:
        HeadlessException - if GraphicsEnvironment.isHeadless returns true
        See Also:
        GraphicsEnvironment.isHeadless()
      • Checkbox

        public Checkbox(String label,
                        boolean state,
                        CheckboxGroup group)
                 throws HeadlessException
        Constructs a Checkbox with the specified label, set to the specified state, and in the specified check box group.
        Parameters:
        label - a string label for this check box, or null for no label.
        state - the initial state of this check box.
        group - a check box group for this check box, or null for no group.
        Throws:
        HeadlessException - if GraphicsEnvironment.isHeadless returns true
        Since:
        JDK1.1
        See Also:
        GraphicsEnvironment.isHeadless()
      • Checkbox

        public Checkbox(String label,
                        CheckboxGroup group,
                        boolean state)
                 throws HeadlessException
        Creates a check box with the specified label, in the specified check box group, and set to the specified state.
        Parameters:
        label - a string label for this check box, or null for no label.
        group - a check box group for this check box, or null for no group.
        state - the initial state of this check box.
        Throws:
        HeadlessException - if GraphicsEnvironment.isHeadless returns true
        Since:
        JDK1.1
        See Also:
        GraphicsEnvironment.isHeadless()
    • Method Detail

      • getLabel

        public String getLabel()
        Gets the label of this check box.
        Returns:
        the label of this check box, or null if this check box has no label.
        See Also:
        setLabel(String)
      • setLabel

        public void setLabel(String label)
        Sets this check box's label to be the string argument.
        Parameters:
        label - a string to set as the new label, or null for no label.
        See Also:
        getLabel()
      • getState

        public boolean getState()
        Determines whether this check box is in the "on" or "off" state. The boolean value true indicates the "on" state, and false indicates the "off" state.
        Returns:
        the state of this check box, as a boolean value
        See Also:
        setState(boolean)
      • setState

        public void setState(boolean state)
        Sets the state of this check box to the specified state. The boolean value true indicates the "on" state, and false indicates the "off" state.

        Note that this method should be primarily used to initialize the state of the checkbox. Programmatically setting the state of the checkbox will not trigger an ItemEvent. The only way to trigger an ItemEvent is by user interaction.

        Parameters:
        state - the boolean state of the check box
        See Also:
        getState()
      • getCheckboxGroup

        public CheckboxGroup getCheckboxGroup()
        Determines this check box's group.
        Returns:
        this check box's group, or null if the check box is not part of a check box group.
        See Also:
        setCheckboxGroup(CheckboxGroup)
      • setCheckboxGroup

        public void setCheckboxGroup(CheckboxGroup g)
        Sets this check box's group to the specified check box group. If this check box is already in a different check box group, it is first taken out of that group.

        If the state of this check box is true and the new group already has a check box selected, this check box's state is changed to false. If the state of this check box is true and the new group has no check box selected, this check box becomes the selected checkbox for the new group and its state is true.

        Parameters:
        g - the new check box group, or null to remove this check box from any check box group
        See Also:
        getCheckboxGroup()
      • getListeners

        public <T extends EventListener> T[] getListeners(Class<T> listenerType)
        Returns an array of all the objects currently registered as FooListeners upon this Checkbox. 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 Checkbox 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 checkbox, 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 check box. If the event is an instance of ItemEvent, this method 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 check box 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(java.awt.event.ItemListener), Component.enableEvents(long)
      • paramString

        protected String paramString()
        Returns a string representing the state of this Checkbox. 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 check box
      • getAccessibleContext

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


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