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Events

Events. Wiring together objects, code, and actions. Events. An ‘event’ is something that the user does move the mouse push down on a key let up on a key click the mouse button … A program should usually respond to these events This happens by attaching ‘code’ to an ‘event’. EventButton

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Events

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  1. Events Wiring together objects, code, and actions

  2. Events • An ‘event’ is something that the user does • move the mouse • push down on a key • let up on a key • click the mouse button • … • A program should usually respond to these events • This happens by attaching ‘code’ to an ‘event’

  3. EventButton «constructor» + EventButton( String txt) «query» + intgetX( ) + intgetY( ) + intgetWidth( ) + intgetHeight( ) + String getText( ) «update» + repaint() + setSize( int, int ) + setText( String ) «event handler» + actionPerformed( ActionEvent ) EventButton • An EventButton • is a Component that when clicked • invokes the actionPerformed method • Write a program to: • Place a button on the window • Draw a “ball” • When the button is pressed, the circle is moved right by 5 pixels

  4. A Solution import java.awt.event.*; import java.awt.*; public class RightButton extends EventButton { private Oval dot; public RightButton(int x, int y, int w, int h, Oval c) { super(“Move Right”); setBounds(x,y,w,h); dot = c; } public void actionPerformed(ActionEvent e) { dot.setLocation(dot.getX() + 5, dot.getY()); dot.repaint(); } }

  5. The Client import javax.swing.*; public class OvalController { public OvalController() { JFrame win = new JFrame(“Demo”); win.setSize(300, 300); win.setLayout(null); Oval oval = new Oval(50,50,50,50); win.add(oval); RightButtonrButton= new RightButton(5, 5, 100, 20, oval); win.add(rButton, 0); win.repaint(); win.setVisible(true); } } Can we make program with two buttons. One moving the circle left and another moving it right? Image courtesy http://www.flickr.com/photos/tmab2003/3464087290/sizes/z/in/photostream/

  6. A Solution import java.awt.event.*; import java.awt.*; public class LeftButtonextends EventButton { private Oval dot; public LeftButton(int x, int y, int w, in th, Oval c) { super(“Move Left”); setBounds(x,y,w,h); dot = c; } public void actionPerformed(ActionEvent e) { dot.setLocation(dot.getX() - 5, dot.getY()); dot.repaint(); } }

  7. The Client import javax.swing.*; public class OvalController { public OvalController() { JFrame win = new JFrame(“Demo”); win.setSize(300, 300); win.setLayout(null); Oval oval = new Oval(50,50,50,50); win.add(oval); RightButtonrButton= new RightButton(5, 5, 100, 20, oval); win.add(rButton, 0); LeftButtonlButton = new LeftButton(5, 30, 100, 20, oval); win.add(lButton); win.repaint(); win.setVisible(true); } } Image courtesy http://www.flickr.com/photos/tmab2003/3464087290/sizes/z/in/photostream/

  8. Another Way (Callbacks) • It is often useful to write a button class that doesn’t know anything about an Oval (or any other object that it is meant to operate on) • The button might command another object to perform the operation. • The other object is typically the controller.

  9. The Client public class OvalController { Oval oval; public OvalController() { JFrame win = new JFrame(“Demo”); win.setSize(300, 300); win.setLayout(null); oval = new Oval(50,50,50,50); win.add(oval); RightButtonrButton= new RightButton(5, 5, 100, 20, oval); win.add(rButton, 0); LeftButtonlButton = new LeftButton(5, 30, 100, 20, oval); win.add(lButton); win.repaint(); win.setVisible(true); } public void moveLeft() { oval.setLocation(oval.getX()-5, oval.getY()); oval.repaint(); } public void moveRight() { oval.setLocation(oval.getX()+5, oval.getY()); oval.repaint(); } } Make the oval an instance variable so it can be used in two new methods. These methods are callback methods. The buttons will “call-back” to them when pushed. Image courtesy http://www.flickr.com/photos/tmab2003/3464087290/sizes/z/in/photostream/

  10. Another Way import java.awt.event.*; public class LeftButton extends EventButton{ private OvalControllercontroller; public LeftButton(int x, int y, int w, int h, OvalController c) { super(“Move Left”); setBounds(x, y, w, h); controller = c; } public void actionPerformed(ActionEvent e) { controller.moveLeft(); } } import java.awt.event.*; public class RightButtonextends EventButton{ // other code omitted public void actionPerformed(ActionEvent e) { controller.moveRight(); } }

  11. EventTextField «constructor» + EventTextField( String txt) «query» + intgetX() + intgetY() + intgetWidth() + intgetHeight() + Color getParent() + String getText() . . . «update» + void repaint() + void setBounds( int, int, int, int ) + void setSize( int, int ) + void setLocation( int, int ) + void setText( String ) . . . «event handler» + void actionPerformed( actionEvent ) Text Fields • A text field is a way for users to type in textual information. • An EventTextField is • A Component • A JTextField

  12. Example import java.awt.event.*; public class OvalSizerField extends EventTextField { private Oval oval; public OvalSizerField(int x, int y, int w, int h, Oval c) { super(c.getWidth() + “”); setBounds(x, y, w, h); oval = c; } public void actionPerformed(ActionEvent e) { String fieldText = getText(); intnumericValue = new Scanner(fieldText).nextInt(); oval.setSize(numericValue, numericValue); } }

  13. The Client import javax.swing.*; public class OvalController { public OvalController() { JFrame win = new JFrame(“Demo”); win.setSize(300, 300); win.setLayout(null); Oval oval = new Oval(50,50,50,50); win.add(oval); OvalSizerField f = new OvalSizerField(5, 5, 100, 20, oval); win.add(f); win.repaint(); win.setVisible(true); } } Image courtesy http://www.flickr.com/photos/tmab2003/3464087290/sizes/z/in/photostream/

  14. Sliders • A slider represents a single integer value. • The value is within a range of integers [min, max] • The value is controlled by the position of the slider • To the left: value is min • To the right: value is max • Elsewhere: a value in [min, max]

  15. EventSlider Crash Course EventSlider + static final intHORIZONTAL + static final intVERTICAL «constructor» + EventSlider( int, int, int, int ) «query» + intgetX() + intgetY() + intgetWidth() + intgetHeight() + intgetMaximum() + intgetMinimum() + Container getParent() + intgetValue() . . . «update» + void repaint() + void setBounds( int, int, int, int ) + void setSize( int, int ) + void setLocation( int, int ) + void setMinimum( int ) + void setMaximum( int ) + void setValue( int ) . . . «event handler» + void stateChanged(javax.swing.event.ChangeEvent) knob getValue() getMinimum() getMaximum() assigns new values to HORIZONTAL or VERTICAL getMinimum(), getMaximum() & getValue() called when user adjusts the knob or arrow buttons

  16. Example • Write a program to use three sliders to change the color of an oval. Each slider controls the amount of red, green or blue in the color of the on-screen oval.

  17. Type Conformance • For any class C, an object V conforms to C if • V is an object of that exact type • OR V is a subclass of class C • For assignment of the form • VAR = EXPRESSION; • The EXPRESSION must conform to the class of VAR • For a method of the form • TYPE NAME(type1 name1, type2 name2, …) {…} • All actual parameters must conform to the specified types

  18. Conformance Write a method to return true if the height of a Rectangle is 10 pixels or greater and false otherwise. public boolean isTall(Rectangle r) { return r.getHeight() >= 10; } Write a method to return true if the height of an Oval is 10 pixels or greater and false otherwise. public boolean isTall(Oval o) { return o.getHeight() >= 10; } Write a method to return true if the height of an Oval or Rectangle or Line is 10 pixels or greater and false otherwise. public boolean isTall(Component v) { return v.getHeight() >= 10; } Oval oval = new Oval(); Rectangle rect = new Rectangle(); SelectableRectangle rect2 = new ASelectableRectangle(); …isTall(rect)… …isTall(oval)… …isTall(rect2)…

  19. Dynamic Conformance Testing • The instanceof operator tests conformance • Syntax: • ExpressioninstanceofClassName • Semantics: • Binary boolean-valued infix operator • Left-hand side is an object • Right-hand side is the name of a class • returns true if the LHS conforms to the RHS and false otherwise

  20. Conformance Write a method that accepts a Component object. If the object conforms to Rectangle then move it right by 5 pixels. If the object conforms to Oval then move it left by 5 pixels. All other Components should move down by 5 pixels. public void move(Component v) { int dx = 0, dy = 0; if(v instanceof Rectangle) { dx = 5; } else if(v instanceof Oval) { dx = -5; } else { dy = 5; } v.setLocation(v.getX() + dx, v.getY() + dy); }

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