Iterator_Pattern

package iterator_pattern;

public abstract class Aggregate {
    public abstract Iterator createIterator();
}

package iterator_pattern;

import java.util.ArrayList;

public class ConcreteAggregate extends Aggregate{
    private ArrayList<Object> items = new ArrayList<Object>();
    @Override
    public Iterator createIterator() {
        return new ConcreteIterator(this);
    }
    public int getCount() {
        return items.size();
    }
    public Object getItem(int index) {//The basic method:get
        return items.get(index);
    }
    public void setItem(int index,Object value) {//The basic method:set
        items.add(index, value);
    }
}

package iterator_pattern;

public abstract class Iterator {
    public abstract Object first();
    public abstract Object next();
    public abstract boolean isDone();
    public abstract Object currentItem();
}

package iterator_pattern;

public class ConcreteIterator extends Iterator{
    private ConcreteAggregate aggregate;
    private int current = 0;
    public ConcreteIterator(ConcreteAggregate aggregate) {
        this.aggregate = aggregate;
        current = aggregate.getCount() - 1;//descend
    }
    @Override
    public Object first() {
        // TODO Auto-generated method stub
        // return aggregate.getItem(0);
        return aggregate.getItem(aggregate.getCount() - 1);
    }
    @Override
    public Object next() {
        // TODO Auto-generated method stub
        Object tmp = null;
        // current++;
        current--;
        //if(current<aggregate.getCount()) {
        if(current >= 0) {
            tmp = aggregate.getItem(current);
        }
        return tmp;
    }
    @Override
    public boolean isDone() {
        // TODO Auto-generated method stub
        // return current>=aggregate.getCount() ? true:false;
        return current < 0 ? true:false;
    }
    @Override
    public Object currentItem() {
        // TODO Auto-generated method stub
        return aggregate.getItem(current);
    }
}

package iterator_pattern;

public class Main {
    public static void main(String args[]) {
        ConcreteAggregate a = new ConcreteAggregate();
        a.setItem(0, "apple");
        a.setItem(1, "banana");
        a.setItem(2, "orange");
        a.setItem(3, "grape");
        a.setItem(4, "pear");
        a.setItem(5, "watermelon");
        Iterator i = new ConcreteIterator(a);
        Object item = i.first();
        System.out.println(item);
        while(!i.isDone()) {
            System.out.println(i.currentItem());
            i.next();
        }
    }
}
This is a general introduction to the 23 design patterns：
https://blog.youkuaiyun.com/GZHarryAnonymous/article/details/81567214

See more source code:[GZHarryAnonymous](https://github.com/GZHarryAnonymous/Design_Pattern)