Draw a shape with a different color (JavaFX)
richardxmercado
CSC255_JavaFX_event.pdf
JAVAFX - EVENT-DRIVEN PROGRAMMING
PROFESSOR SYLVIA YEUNG
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MOTIVATIONS
SUPPOSE YOU WANT TO WRITE A GUI
PROGRAM THAT LETS THE USER ENTER A
LOAN AMOUNT, ANNUAL INTEREST
RATE, AND NUMBER OF YEARS AND
CLICK THE COMPUTE PAYMENT BUTTON
TO OBTAIN THE MONTHLY PAYMENT
AND TOTAL PAYMENT. HOW DO YOU
ACCOMPLISH THE TASK? YOU HAVE TO
USE EVENT-DRIVEN PROGRAMMING TO
WRITE THE CODE TO RESPOND TO THE
BUTTON-CLICKING EVENT.
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PROCEDURAL VS. EVENT-DRIVEN PROGRAMMING
PROCEDURAL PROGRAMMING IS EXECUTED IN PROCEDURAL ORDER.
IN EVENT-DRIVEN PROGRAMMING, CODE IS EXECUTED UPON ACTIVATION
OF EVENTS.
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SAY HELLO
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EVENTS
AN EVENT CAN BE DEFINED AS A TYPE OF
SIGNAL TO THE PROGRAM THAT SOMETHING
HAS HAPPENED.
THE EVENT IS GENERATED BY EXTERNAL USER
ACTIONS SUCH AS MOUSE MOVEMENTS,
MOUSE CLICKS, OR KEYSTROKES.
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EVENT CLASSES
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EVENT INFORMATION
AN EVENT OBJECT CONTAINS WHATEVER PROPERTIES ARE PERTINENT TO THE
EVENT.
YOU CAN IDENTIFY THE SOURCE OBJECT OF THE EVENT USING THE
GETSOURCE() INSTANCE METHOD IN THE EVENTOBJECT CLASS.
THE SUBCLASSES OF EVENTOBJECT DEAL WITH SPECIAL TYPES OF EVENTS,
SUCH AS BUTTON ACTIONS, WINDOW EVENTS, MOUSE MOVEMENTS, AND
KEYSTROKES.
TABLE 1 LISTS EXTERNAL USER ACTIONS, SOURCE OBJECTS, AND EVENT TYPES
GENERATED.
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TABLE 1: SELECTED USER ACTIONS AND HANDLERS
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HANDLING GUI EVENTS
SOURCE OBJECT (E.G., BUTTON)
LISTENER OBJECT CONTAINS A METHOD FOR
PROCESSING THE EVENT.
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THE DELEGATION MODEL
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THE DELEGATION MODEL: EXAMPLE
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Button btOK = new Button("OK");
OKHandlerClass handler = new OKHandlerClass();
btOK.setOnAction(handler);//register
Source object listener object
class OKHandlerClass implements EventHandler<ActionEvent> {
@Override
public void handle(ActionEvent e) {
System.out.println("OK button clicked");
}
}
INNER CLASS
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Button btn = new Button(“Say ‘Hello World’");
SayHelloEvent handler = new SayHelloEvent();
btn.setOnAction(handler);//register
TASTE OF EVENT-DRIVEN PROGRAMMING
THE EXAMPLE DISPLAYS A BUTTON IN THE FRAME. A MESSAGE IS DISPLAYED ON THE CONSOLE WHEN A BUTTON IS CLICKED.
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TRACE EXECUTION
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public class HandleEvent extends Application {
public void start(Stage primaryStage) {
…
OKHandlerClass handler1 = new OKHandlerClass();
btOK.setOnAction(handler1);
CancelHandlerClass handler2 = new CancelHandlerClass();
btCancel.setOnAction(handler2);
…
primaryStage.show(); // Display the stage
}
}
class OKHandlerClass implements EventHandler<ActionEvent> {
@Override
public void handle(ActionEvent e) {
System.out.println("OK button clicked");
}
}
1. Start from the
main method to
create a window and
display it
animation
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TRACE EXECUTION
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public class HandleEvent extends Application {
public void start(Stage primaryStage) {
…
OKHandlerClass handler1 = new OKHandlerClass();
btOK.setOnAction(handler1);
CancelHandlerClass handler2 = new CancelHandlerClass();
btCancel.setOnAction(handler2);
…
primaryStage.show(); // Display the stage
}
}
class OKHandlerClass implements EventHandler<ActionEvent> {
@Override
public void handle(ActionEvent e) {
System.out.println("OK button clicked");
}
}
animation
2. Click OK
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TRACE EXECUTION
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public class HandleEvent extends Application {
public void start(Stage primaryStage) {
…
OKHandlerClass handler1 = new OKHandlerClass();
btOK.setOnAction(handler1);
CancelHandlerClass handler2 = new CancelHandlerClass();
btCancel.setOnAction(handler2);
…
primaryStage.show(); // Display the stage
}
}
class OKHandlerClass implements EventHandler<ActionEvent> {
@Override
public void handle(ActionEvent e) {
System.out.println("OK button clicked");
}
}
animation
3. The JVM invokes
the listener’s handle
method
INNER CLASS
LISTENER
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Two source objects and
two listener objects within
two Inner classes
INNER CLASS LISTENERS
A LISTENER CLASS IS DESIGNED SPECIFICALLY
TO CREATE A LISTENER OBJECT FOR A GUI
COMPONENT (E.G., A BUTTON). IT WILL NOT
BE SHARED BY OTHER APPLICATIONS. SO, IT
IS APPROPRIATE TO DEFINE THE LISTENER
CLASS INSIDE THE FRAME CLASS AS AN
INNER CLASS.
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INNER CLASSES
INNER CLASS: A CLASS IS A MEMBER OF ANOTHER
CLASS.
ADVANTAGES: IN SOME APPLICATIONS, YOU CAN
USE AN INNER CLASS TO MAKE PROGRAMS SIMPLE.
AN INNER CLASS CAN REFERENCE THE DATA AND
METHODS DEFINED IN THE OUTER CLASS IN WHICH IT
NESTS, SO YOU DO NOT NEED TO PASS THE
REFERENCE OF THE OUTER CLASS TO THE
CONSTRUCTOR OF THE INNER CLASS.
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INNER CLASSES, CONT.
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INNER CLASSES (CONT.)
INNER CLASSES CAN MAKE PROGRAMS SIMPLE AND CONCISE.
AN INNER CLASS SUPPORTS THE WORK OF ITS CONTAINING OUTER
CLASS AND IS COMPILED INTO A CLASS NAMED
OUTERCLASSNAME$INNERCLASSNAME.CLASS. FOR EXAMPLE, THE
INNER CLASS INNERCLASS IN OUTERCLASS IS COMPILED INTO
OUTERCLASS$INNERCLASS.CLASS.
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INNER CLASSES (CONT.)
AN INNER CLASS CAN BE DECLARED PUBLIC, PROTECTED, OR
PRIVATE SUBJECT TO THE SAME VISIBILITY RULES APPLIED TO A
MEMBER OF THE CLASS.
AN INNER CLASS CAN BE DECLARED STATIC.
A STATIC INNER CLASS CAN BE ACCESSED USING THE OUTER
CLASS NAME. A STATIC INNER CLASS CANNOT ACCESS NONSTATIC
MEMBERS OF THE OUTER CLASS
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Two source objects and
ONE listener object within
one Inner classes
getSource() method object
ANONYMOUS INNER CLASSES
AN ANONYMOUS INNER CLASS MUST ALWAYS EXTEND A
SUPERCLASS OR IMPLEMENT AN INTERFACE, BUT IT CANNOT HAVE
AN EXPLICIT EXTENDS OR IMPLEMENTS CLAUSE.
AN ANONYMOUS INNER CLASS MUST IMPLEMENT ALL THE ABSTRACT
METHODS IN THE SUPERCLASS OR IN THE INTERFACE.
AN ANONYMOUS INNER CLASS ALWAYS USES THE NO-ARG
CONSTRUCTOR FROM ITS SUPERCLASS TO CREATE AN INSTANCE. IF
AN ANONYMOUS INNER CLASS IMPLEMENTS AN INTERFACE, THE
CONSTRUCTOR IS OBJECT().
AN ANONYMOUS INNER CLASS IS COMPILED INTO A CLASS NAMED
OUTERCLASSNAME$N.CLASS. FOR EXAMPLE, IF THE OUTER CLASS
TEST HAS TWO ANONYMOUS INNER CLASSES, THESE TWO CLASSES
ARE COMPILED INTO TEST$1.CLASS AND TEST$2.CLASS.
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ANONYMOUS INNER CLASSES (CONT.)
INNER CLASS LISTENERS CAN BE SHORTENED USING
ANONYMOUS INNER CLASSES. AN ANONYMOUS INNER
CLASS IS AN INNER CLASS WITHOUT A NAME. IT
COMBINES DECLARING AN INNER CLASS AND CREATING
AN INSTANCE OF THE CLASS IN ONE STEP. AN
ANONYMOUS INNER CLASS IS DECLARED AS FOLLOWS:
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new SuperClassName/InterfaceName() {
// Implement or override methods in superclass or interface
// Other methods if necessary
}
ANONYMOUS INNER CLASSES (CONT.)
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Anonymous Inner classes
Lambda Expression
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Two source objects and
ONE listener object
NO Inner classes
SIMPLIFYING EVENT HANDING USING LAMBDA EXPRESSIONS
LAMBDA EXPRESSION IS A NEW FEATURE IN JAVA 8. LAMBDA
EXPRESSIONS CAN BE VIEWED AS AN ANONYMOUS METHOD
WITH A CONCISE SYNTAX. FOR EXAMPLE, THE FOLLOWING
CODE IN (A) CAN BE GREATLY SIMPLIFIED USING A LAMBDA
EXPRESSION IN (B) IN THREE LINES.
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btEnlarge.setOnAction(
new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent e) {
// Code for processing event e
}
}
});
(a) Anonymous inner class event handler
btEnlarge.setOnAction(e -> {
// Code for processing event e
});
(b) Lambda expression event handler
BASIC SYNTAX FOR A LAMBDA EXPRESSION
THE BASIC SYNTAX FOR A LAMBDA EXPRESSION IS EITHER
(TYPE1 PARAM1, TYPE2 PARAM2, ...) -> EXPRESSION
OR
(TYPE1 PARAM1, TYPE2 PARAM2, ...) -> { STATEMENTS; }
THE DATA TYPE FOR A PARAMETER MAY BE EXPLICITLY DECLARED OR IMPLICITLY
INFERRED BY THE COMPILER. THE PARENTHESES CAN BE OMITTED IF THERE IS ONLY
ONE PARAMETER WITHOUT AN EXPLICIT DATA TYPE.
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sourceObj.setOnAction ((ActionEvent e ) -> {expressions; } );
THE MOUSEEVENT CLASS
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THE KEYEVENT CLASS
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THE KEYCODE CONSTANTS
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LISTENERS FOR OBSERVABLE OBJECTS
YOU CAN ADD A LISTENER TO PROCESS A VALUE CHANGE IN AN
OBSERVABLE OBJECT.
AN INSTANCE OF OBSERVABLE IS KNOWN AS AN OBSERVABLE OBJECT,
WHICH CONTAINS THE ADDLISTENER(INVALIDATIONLISTENER
LISTENER) METHOD FOR ADDING A LISTENER.
ONCE THE VALUE IS CHANGED IN THE PROPERTY, A LISTENER IS
NOTIFIED. THE LISTENER CLASS SHOULD IMPLEMENT THE
INVALIDATIONLISTENER INTERFACE, WHICH USES THE
INVALIDATED(OBSERVABLE O) METHOD TO HANDLE THE PROPERTY
VALUE CHANGE. EVERY BINDING PROPERTY IS AN INSTANCE OF
OBSERVABLE.
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The program registers the listeners for
the stack pane’s width and height
properties. When the user resizes the
window, the pane’s size is changed, so
the listeners are called to invoke the
resize() method to change the size of the
circle and rectangle
