迭代器模式（Interator Pattern）

public interface Iterator {
    public void first();              //将游标指向第一个元素
    public void next();               //将游标指向下一个元素
    public boolean hasNext();         //判断是否存在下一个元素
    public Object currentItem();      //获取游标指向的当前元素
}

public class ConcreteIterator implements Iterator {
    private ConcreteAggregate objects; //维持一个对具体聚合对象的引用，以便于访问存储在聚合对象中的数据
    private int cursor;         //定义一个游标，用于记录当前访问位置
    public ConcreteIterator(ConcreteAggregate objects) {
        this.objects=objects;
    }
    public void first() {  ......  }		
    public void next() {  ......  }
    public boolean hasNext( ) {  ......  }	
    public Object currentItem( ) {  ......  }
}

public interface Aggregate {
    Iterator createIterator( );
}

public class ConcreteAggregate implements Aggregate {	
    ......	
    public Iterator createIterator( ) {
        return new ConcreteIterator(this);
    }
    ......
}

public interface TVInterator {

    void setChannel(int i);
    Object currentChannel();
    void next();
    void previous();
    boolean isLast();
    boolean isFirst();

}

public interface Television {

    TVInterator createInterator();

}

public class SkyworthTelevision implements Television{

    private Object[] obj = {"CCTV-1","CCTV-2","CCTV-3","CCTV-4","CCTV-5","CCTV-6"};

    @Override
    public TVInterator createInterator() {
        return new SkyworthInterator(obj);
    }

}

public class TCLTelevision implements Television{

    private Object[] obj = {"湖南卫视","上海卫视","山西卫视","河北卫视","上海卫视","北京卫视"};

    @Override
    public TVInterator createInterator() {
        return new SkyworthInterator(obj);
    }

}

public class SkyworthInterator implements TVInterator{

    private int currentIndex = 0;
    private Object obj[];

    public SkyworthInterator(Object[] obj) {
        this.obj = obj;
    }

    @Override
    public void setChannel(int i) {
        currentIndex = i;
    }

    @Override
    public Object currentChannel() {
        return obj[currentIndex];
    }

    @Override
    public void next() {
        if (currentIndex < obj.length){
            currentIndex ++;
        }
    }

    @Override
    public void previous() {
        if (currentIndex > 0){
            currentIndex --;
        }
    }

    @Override
    public boolean isLast() {
        return currentIndex == obj.length;
    }

    @Override
    public boolean isFirst() {
        return currentIndex ==0;
    }
}

public class TCLInterator implements TVInterator{

    private int currentIndex = 0;
    private Object obj[];

    public TCLInterator(Object[] obj) {
        this.obj = obj;
    }

    @Override
    public void setChannel(int i) {
        currentIndex = i;
    }

    @Override
    public Object currentChannel() {
        return obj[currentIndex];
    }

    @Override
    public void next() {
        if (currentIndex < obj.length){
            currentIndex ++;
        }
    }

    @Override
    public void previous() {
        if (currentIndex > 0){
            currentIndex --;
        }
    }

    @Override
    public boolean isLast() {
        return currentIndex == obj.length;
    }

    @Override
    public boolean isFirst() {
        return currentIndex ==0;
    }
}

public class Client {

    public static void display(Television tv){
        TVInterator interator = tv.createInterator();
        System.out.println("电视机频道：");
        while (!interator.isLast()){
            System.out.println(interator.currentChannel().toString());
            interator.next();
        }
    }
    public static void reverseDisplay(Television tv){
        TVInterator interator = tv.createInterator();
        interator.setChannel(6);
        System.out.println("逆向遍历电视机频道：");
        while (!interator.isFirst()){
            interator.previous();
            System.out.println(interator.currentChannel().toString());
        }
    }

    public static void main(String a[]) {
        Television tv = (Television) XMLUtil.getBean();
        display(tv);
        System.out.println("===============");
        reverseDisplay(tv);
    }

}