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What are Objects like so far? They offer Services:- Reading an number from the console- Storing data- Keeping an account status An interface often serves as users‘ instructions for ausing class:Using Class Interface Service Classknowsimplements Objects are passive, they only work when called upon- readNumber(), transferSum()(c)schmiedecke 06 Inf1-7a: Animation 2

Active Objects• Balls in BallWorld behave differently• They do react to impulses (clicking), but they alsowork without outer impulse.• The general situation is similar,BallWorld Ball Exploderknowsimplements• but Ball Objects behave differently.(c)schmiedecke 06 Inf1-7a: Animation 3

How does Object Activity Happen?ModellCall-Center• Prozedurales Functional concept: Modell:nur objects scheinbar seem active, aktive Objekte,• reagieren react to stimuli nur auf of aAnfrage calling (durch process einen rufenden• Prozess) BallWorld calls the act() method of all ist Ball objects• in Ballworld an indefinte ruft in loop einer Endlosschleife immer wiederact()ModellService• OO concept:objects are independant, interacting units• act independantly (also react to stimuli)• Every Ball object has its own process which indefinitelycalls its act() method(c)schmiedecke 06 Inf1-7a: Animation 4

Counter and Timer(c)schmiedecke 06 Inf1-7a: Animation 5

Common Interfacepublic interface Incrementor {}public void increment();public void reset();public int getValue();public class Counter implements Incrementor {protected int value = 0;public void increment() { value++; }public void reset() { value = 0; }public int getValue() { return value; }}public class Timer extends Counter implements Animate {public void act() { increment(); }} Only(c)schmiedecke 06 Inf1-7a: Animation difference 6

... who calls act()?Processes and ThreadsA process is an instruction follower which is started andcontrolled by the operating system.An instruction follower which is started and controlled withina process is called a Thread ("Lebens-Faden").In Java, threads are instances of Thread .A Thread object can be started.Once started, it is "alive" and can animate otherobjects (e.g. call act()).(c)schmiedecke 06 Inf1-7a: Animation 7

AnimatorThread animates Timeract!AnimatorThreadinstance(has its own Thread)"animates" passive objectof type Animate(without a Thread)(c)schmiedecke 06 Inf1-7a: Animation 8

AnimatorThread animates Ballact!ExploderAnimatorThreadinstance(has its own Thread)"animates" passive objectof type Animate(without a Thread)(c)schmiedecke 06 Inf1-7a: Animation 9

The AnimatorThread ClassAnimatorThreadknowsAnimateimplementsAnimatedObject Every instance of AnimatorThread possesses its own thread. Its constructor attaches it to a (passive) Animate object which itanimates. Once started, it calls the Aminate's act() method indefinitely.Animate timer = new Timer();AnimatorThread timerThread = new AnimatorThread(timer);timerThread.startExecution();Animate :timer xBall = new Exploder();AnimatorThreadAnimate:timertimerThread = new AnimatorThread(xBall);timerThread.startExecution();kenntimplementiert(c)schmiedecke 06 Inf1-7a: Animation 10

package cs101.lang;AnimatorThread Servicespublic class AnimatorThread extends Thread {public AnimatorThread(Animate animatedObject);public void startExecution(); //indefinite looppublic void stopExecution (); //for goodpublic void suspendExecution (); //temporarilypublic void resumeExecution (); //following suspend}public void setSleepMinInterval(long millis);public void setSleepRange(long millis);(c)schmiedecke 06 Inf1-7a: Animation 11

Set Alivepublic class BallWorld extends World{// ...// method is called when button is pressedpublic void startExploder() {// create and launch ballExploder xBall = new Exploder();this.addBall(xBall);}// animate ballAnimatorThread explThread =new AnimatorThread(xBall);explThread.startExecution();}//...(c)schmiedecke 06 Inf1-7a: Animation 12

Create Aliveclass Throbber implements Ball, Animate {World world;// Animation in the constructorpublic Throbber(World world) {this(); // initialize x, y, radiusthis.world = world;}// create and grasp your own threadAnimatorThread throbThread =new AnimatorThread(this);throbThread.startExecution();}public void act() { // called by explThread}//...(c)schmiedecke 06 Inf1-7a: Animation 13

Active Timerpublic class Timer extends Counter implementsAnimate {private AnimatorThread timerThread;public Timer () {timerThread = new AnimatorThread(this);timerThread.startExecution();}}public void act() {increment();}(c)schmiedecke 06 Inf1-7a: Animation 14

Delayed Startpublic class Timer extends Counter implementsAnimate {private AnimatorThread timerThread;}public Timer () {timerThread = new AnimatorThread(this);}public void init() {timerThread.startExecution();}public void act() {increment();}Use init() formethods thatare called onlyonce for setup.(c)schmiedecke 06 Inf1-7a: Animation 15

Now put it all into the GUI:public class VisibleTimer extends Timer {private AnimationGUI gui;public VisibleTimer(AnimationGUI gui){super();this.gui = gui;}public void increment() {super.increment();gui.updateTimer(value); // shows value in GUI}}public void reset() {super.reset();gui.updateTimer(0); // shows 0 in GUI}(c)schmiedecke 06 Inf1-7a: Animation 16

The AnimationGUI Class(for the curious only...) paints the graphical user interface instantiates VisibleCounter and VisibleTimerYou can download AnimationGui,everything else is up to you towrite. calls on button action their methods increment() undreset() defines two output methods, updateCounter() andupdateTimer(), which are called by VisibleCounter andVisibleTimer on every increment() or reset(). The buttons "pause" and "cont." are used to call two Timermethods, pause() and continue(), which have not yetbeen implemented (your job ) (Hint: It is common practice to put the main method into the GUIclass)(c)schmiedecke 06 Inf1-7a: Animation 17

Observing an Object(two active objects involved)public class CountingMonitor implements Animate {private Counter whoToMonitor;private AnimatorThread mover;public CountingMonitor(Counter whoToMonitor ) {this.whoToMonitor = whoToMonitor;}this.mover = new AnimatorThread( this );this.mover.startExecution();public void act(){ Console.println( "The timer says " +whoToMonitor.getValue() );}Gets to know itsobject in theconstructorTry it!}Timer timer = new Timer(); // live creationCountingMonitor monitor = new CountingMonitor(timer);(c)schmiedecke 06 Inf1-7a: Animation 18

How Many Threads Can You Get? Any number. An object can – when it's method is executed- create any number of new threads. Result: Tree structure of running threads.(c)schmiedecke 06 Inf1-7a: Animation 19

Java Standard Threadspackage java.lang;Interface Runnable{ public void run(); } // c.f. Animatepublic class Thread { // c.f. AnimatorThreadpublic Thread(Runnable runnerObject);public void start();public boolean isAlive();public void interrupt();public void join();}static void sleep(long millis)throws InterruptedException;static void yield();// ...(c)schmiedecke 06 Inf1-7a: Animation 20

Thread vs. AnimatorThread Similar concept:so, if you can use AnimatorThread, you can work with Thread as well. The animated Object must implement Runnable, rather thanAnimateRunnable ticker; // has a run() methodThread tickerthread = new Thread(ticker);tickerThread.start(); // calls run() ONLY ONCE Thread has NO indefinite loop –if wanted, implement it inside the run() method. Thread's methods suspend, resume and stop are not quite safe(supposedly mended in Java5) Thread has an unfair scheduler.(c)schmiedecke 06 Inf1-7a: Animation 21

Understanding Programm StartThe operating system starts the virtualmachine ProcessThe virtual machine starts a newThread, in which it calls the mainmethodApplets too are run as VM threads.(c)schmiedecke 06 Inf1-7a: Animation 22

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