Iterator

public interface Collection {
    void add(Object o);
    int size();
}


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public class ArrayList implements Collection {
    private int size=0;
    Object[] os = new Object[10];
    @Override
    public void add(Object o) {
        if(size == os.length){
            Object[] newOs = new Object[os.length*2];
            System.arraycopy(os, 0, newOs, 0, os.length);
            os = newOs;
        }
        os[size] = o;
        size++;
    }

    @Override
    public int size() {
        return size;
    }

    Iterator iterator(){
        ArrayListIterator it = new ArrayListIterator();
        return it;
    }
    class ArrayListIterator implements Iterator{
        int current = 0;
        @Override
        public boolean hasNext() {
            if(current==size)
                return false;
            else { 
                current++;///
                return true;
            }
        }

        @Override
        public Object next() {
            return os[current-1];
        }

    }

}


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import static org.junit.Assert.*;

import org.junit.Assert;
import org.junit.Test;
/**
 * @author Thinkpad
 *
 */
public class ArrayListTest {
    /**
     * Test method for {@link ArrayList#add(java.lang.Object)}.
     */
    @Test
    public void testAdd() {
        String str="test---";
        ArrayList al = new ArrayList();
        for(int i=0;i<3;i++){
            al.add(str+i);
        }
        Iterator it = al.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    } 
}


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public interface Iterator {
    boolean hasNext();
    Object next();
}


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public class LinkedList implements Collection {
    private int size = 0;
    Node head = new Node();
    Node tail = head;

    @Override
    public void add(Object o) {
        Node n = new Node();
        tail.setData(o);
        tail.setNode(n);
        tail = n;
        size++;
    }

    @Override
    public int size() {
        return size;
    }

    Iterator iterator() {
        return new LinkedListIterator();
    }

    private class Node {
        Object data;
        Node node;

        public Object getData() {
            return data;
        }

        public void setData(Object data) {
            this.data = data;
        }

        public Node getNode() {
            return node;
        }

        public void setNode(Node node) {
            this.node = node;
        }
    }

    class LinkedListIterator implements Iterator {
        Node temp = head;
        Node data = temp;
        @Override
        public boolean hasNext() {
            if (temp.node == null)
                return false;
            else {
                data = temp;
                temp = temp.node;
                return true;
            }
        }

        @Override
        public Object next() {
            return data.data;
        }

    }
}


----------
import static org.junit.Assert.*;

import org.junit.Assert;
import org.junit.Test;
/**
 * @author Thinkpad
 *
 */
public class LinkedListTest {

    /**
     * Test method for {@link LinkedList#add(java.lang.Object)}.
     */
    @Test
    public void testAdd() {
        LinkedList ll = new LinkedList();
        ll.add(new String("ni hao a!"));
        ll.add(new String("wo ye hao a!"));
        Iterator it = ll.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }
}