Java设计模式(八)观察者模式 迭代器模式
(十五)观察者模式
观察者模式,定义对象间一对多关系,一个对象状态发生改变,所有依赖于它的对象都收到通知并且自动更新,观察者与被观察者分开。例如邮件订阅、RSS订阅,如果有更新就会邮件通知你。
interface Observers{ public void update(); } class Observer1 implements Observers{ public void update(){ System.out.println("observer1 has received"); } } class Observer2 implements Observers{ public void update(){ System.out.println("observer2 has received"); } } interface Subject { public void add(Observers ob); public void delete(Observers ob); public void notifyObservers(); public void operation(); } abstract class AbstractSubject implements Subject{ private Vector<Observers> vector = new Vector<>(); public void add(Observers ob){ vector.add(ob); } public void delete(Observers ob){ vector.remove(ob); } public void notifyObservers(){ Enumeration<Observers> enumo = vector.elements(); while(enumo.hasMoreElements()){ enumo.nextElement().update(); } } } class MySubject extends AbstractSubject{ public void operation(){ System.out.println("update self"); notifyObservers(); } } public class Observer { public static void main(String[] args){ Subject sub = new MySubject(); sub.add(new Observer1()); sub.add(new Observer2()); sub.operation(); } }(十六)迭代器模式
说到迭代器首先想到 Iterator ,使用迭代器来为顺序访问集合元素提供一种方式。下面是自己的一个集合,当然只能放 int ,简单的实现了 迭代器的功能,当然实际的Java迭代器比这要复杂很多。
interface Collection{ public Iterator iterator(); public Object get(int i); public int size(); public void add(int n); } interface Iterator{ public Object previous(); public Object next(); public boolean hasNext(); public Object first(); } class MyCollection implements Collection{ private int count = 10; private int[] num = new int[count]; public void add(int n){ for(int i = 0;i < num.length;i++){ if(num[i] == 0){ num[i] = n; return; } } } public MyCollection(int count){ this.count = count; } @Override public Iterator iterator() { return new MyIterator(this); } @Override public Object get(int i) { return num[i]; } @Override public int size() { return num.length; } } class MyIterator implements Iterator{ private Collection collection; private int pos = -1; public MyIterator(Collection collection){ this.collection = collection; } @Override public Object previous() { if(pos > 0){ pos--; } return collection.get(pos); } @Override public Object next() { if(pos < collection.size() - 1){ pos ++; } return collection.get(pos); } @Override public boolean hasNext() { if(pos < collection.size() - 1){ return true; }else{ return false; } } @Override public Object first() { pos = 0; return collection.get(pos); } } public class IteratorTest { public static void main(String[] args){ Collection col = new MyCollection(10); for(int i = 0 ; i < 10;i++){ col.add(i * 23); } Iterator it = col.iterator(); while(it.hasNext()){ System.out.println(it.next()); } } }
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