Mega Code Archive
Demonstration of observer pattern
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import java.util.Observable;
import java.util.Observer;
class Library {
private boolean isOpen;
private OpenNotifier oNotify = new OpenNotifier();
private CloseNotifier cNotify = new CloseNotifier();
public Library() {
isOpen = false;
}
public void open() { // Opens its petals
isOpen = true;
oNotify.notifyObservers();
cNotify.open();
}
public void close() { // Closes its petals
isOpen = false;
cNotify.notifyObservers();
oNotify.close();
}
public Observable opening() {
return oNotify;
}
public Observable closing() {
return cNotify;
}
private class OpenNotifier extends Observable {
private boolean alreadyOpen = false;
public void notifyObservers() {
if (isOpen && !alreadyOpen) {
setChanged();
super.notifyObservers();
alreadyOpen = true;
}
}
public void close() {
alreadyOpen = false;
}
}
private class CloseNotifier extends Observable {
private boolean alreadyClosed = false;
public void notifyObservers() {
if (!isOpen && !alreadyClosed) {
setChanged();
super.notifyObservers();
alreadyClosed = true;
}
}
public void open() {
alreadyClosed = false;
}
}
}
class Student {
private String name;
private OpenObserver openObsrv = new OpenObserver();
private CloseObserver closeObsrv = new CloseObserver();
public Student(String nm) {
name = nm;
}
private class OpenObserver implements Observer {
public void update(Observable ob, Object a) {
System.out.println("Student " + name + "'s study time!");
}
}
private class CloseObserver implements Observer {
public void update(Observable ob, Object a) {
System.out.println("Student " + name + "'s bed time!");
}
}
public Observer openObserver() {
return openObsrv;
}
public Observer closeObserver() {
return closeObsrv;
}
}
class Professor {
private String name;
private OpenObserver openObsrv = new OpenObserver();
private CloseObserver closeObsrv = new CloseObserver();
public Professor(String nm) {
name = nm;
}
private class OpenObserver implements Observer {
public void update(Observable ob, Object a) {
System.out.println("Professor " + name + "'s research time!");
}
}
private class CloseObserver implements Observer {
public void update(Observable ob, Object a) {
System.out.println("Professor " + name + "'s bed time!");
}
}
public Observer openObserver() {
return openObsrv;
}
public Observer closeObserver() {
return closeObsrv;
}
}
public class ObservedFlower {
public static void main(String args[]) {
Library f = new Library();
Student ba = new Student("A"), bb = new Student("B");
Professor ha = new Professor("A"), hb = new Professor("B");
f.opening().addObserver(ha.openObserver());
f.opening().addObserver(hb.openObserver());
f.opening().addObserver(ba.openObserver());
f.opening().addObserver(bb.openObserver());
f.closing().addObserver(ha.closeObserver());
f.closing().addObserver(hb.closeObserver());
f.closing().addObserver(ba.closeObserver());
f.closing().addObserver(bb.closeObserver());
f.opening().deleteObserver(hb.openObserver());
f.open();
f.closing().deleteObserver(ba.closeObserver());
f.close();
f.opening().deleteObservers();
f.open();
f.close();
}
}
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