FocusListener or
* FocusAdapter object which registered to receive such events
* using the Component's addFocusListener method. (
* FocusAdapter objects implement the FocusListener
* interface.) Each such listener object gets this FocusEvent when
* the event occurs.
*
* There are two levels of focus events: permanent and temporary. Permanent
* focus change events occur when focus is directly moved from one Component to
* another, such as through a call to requestFocus() or as the user uses the
* TAB key to traverse Components. Temporary focus change events occur when
* focus is temporarily lost for a Component as the indirect result of another
* operation, such as Window deactivation or a Scrollbar drag. In this case,
* the original focus state will automatically be restored once that operation
* is finished, or, for the case of Window deactivation, when the Window is
* reactivated. Both permanent and temporary focus events are delivered using
* the FOCUS_GAINED and FOCUS_LOST event ids; the level may be distinguished in
* the event using the isTemporary() method.
*
* @see FocusAdapter
* @see FocusListener
* @see Tutorial: Writing a Focus Listener
* @see Reference: The Java Class Libraries (update file)
*
* @author Carl Quinn
* @author Amy Fowler
* @version 1.30 12/19/03
* @since 1.1
*/
public class FocusEvent extends ComponentEvent {
/**
* The first number in the range of ids used for focus events.
*/
public static final int FOCUS_FIRST = 1004;
/**
* The last number in the range of ids used for focus events.
*/
public static final int FOCUS_LAST = 1005;
/**
* This event indicates that the Component is now the focus owner.
*/
public static final int FOCUS_GAINED = FOCUS_FIRST; //Event.GOT_FOCUS
/**
* This event indicates that the Component is no longer the focus owner.
*/
public static final int FOCUS_LOST = 1 + FOCUS_FIRST; //Event.LOST_FOCUS
/**
* A focus event can have two different levels, permanent and temporary.
* It will be set to true if some operation takes away the focus
* temporarily and intends on getting it back once the event is completed.
* Otherwise it will be set to false.
*
* @serial
* @see #isTemporary
*/
boolean temporary;
/**
* The other Component involved in this focus change. For a FOCUS_GAINED
* event, this is the Component that lost focus. For a FOCUS_LOST event,
* this is the Component that gained focus. If this focus change occurs
* with a native application, a Java application in a different VM, or with
* no other Component, then the opposite Component is null.
*
* @see #getOppositeComponent
* @since 1.4
*/
transient Component opposite;
/*
* JDK 1.1 serialVersionUID
*/
private static final long serialVersionUID = 523753786457416396L;
/**
* Constructs a FocusEvent object with the
* specified temporary state and opposite Component.
* The opposite Component is the other
* Component involved in this focus change.
* For a FOCUS_GAINED event, this is the
* Component that lost focus. For a
* FOCUS_LOST event, this is the Component
* that gained focus. If this focus change occurs with a native
* application, with a Java application in a different VM,
* or with no other Component, then the opposite
* Component is null.
*
Note that passing in an invalid id results in
* unspecified behavior. This method throws an
* IllegalArgumentException if source
* is null.
*
* @param source the Component that originated the event
* @param id FOCUS_GAINED or FOCUS_LOST
* @param temporary true if the focus change is temporary;
* false otherwise
* @param opposite the other Component involved in the focus change,
* or null
* @throws IllegalArgumentException if source is null
*/
public FocusEvent(Component source, int id, boolean temporary,
Component opposite) {
super(source, id);
this.temporary = temporary;
this.opposite = opposite;
}
/**
* Constructs a FocusEvent object and identifies
* whether or not the change is temporary.
*
Note that passing in an invalid id results in
* unspecified behavior. This method throws an
* IllegalArgumentException if source
* is null.
*
* @param source the Component that originated the event
* @param id an integer indicating the type of event
* @param temporary true if the focus change is temporary;
* false otherwise
* @throws IllegalArgumentException if source is null
*/
public FocusEvent(Component source, int id, boolean temporary) {
this(source, id, temporary, null);
}
/**
* Constructs a FocusEvent object and identifies it
* as a permanent change in focus.
*
Note that passing in an invalid id results in
* unspecified behavior. This method throws an
* IllegalArgumentException if source
* is null.
*
* @param source the Component that originated the event
* @param id an integer indicating the type of event
* @throws IllegalArgumentException if source is null
*/
public FocusEvent(Component source, int id) {
this(source, id, false);
}
/**
* Identifies the focus change event as temporary or permanent.
*
* @return true if the focus change is temporary;
* false otherwise
*/
public boolean isTemporary() {
return temporary;
}
/**
* Returns the other Component involved in this focus change. For a
* FOCUS_GAINED event, this is the Component that lost focus. For a
* FOCUS_LOST event, this is the Component that gained focus. If this
* focus change occurs with a native application, with a Java application
* in a different VM or context, or with no other Component, then null is
* returned.
*
* @return the other Component involved in the focus change, or null
* @since 1.4
*/
public Component getOppositeComponent() {
if (opposite == null) {
return null;
}
return (SunToolkit.targetToAppContext(opposite) ==
AppContext.getAppContext())
? opposite
: null;
}
/**
* Returns a parameter string identifying this event.
* This method is useful for event-logging and for debugging.
*
* @return a string identifying the event and its attributes
*/
public String paramString() {
String typeStr;
switch(id) {
case FOCUS_GAINED:
typeStr = "FOCUS_GAINED";
break;
case FOCUS_LOST:
typeStr = "FOCUS_LOST";
break;
default:
typeStr = "unknown type";
}
return typeStr + (temporary ? ",temporary" : ",permanent") +
",opposite=" + getOppositeComponent();
}
}