设计模式——容器(iterator) 学习笔记

最新推荐文章于 2022-05-06 10:40:36 发布

原创最新推荐文章于 2022-05-06 10:40:36 发布 · 554 阅读

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主要用在容器的遍历上；；容器是指能够容纳其他对象的

模拟数组的容器

package com.bjsxt.iterator;

public class ArrayList {

package com.bjsxt.iterator;

import com.bjsxt.iterator.ArrayList;
public class Test {

public static void main(String[] args) {

  ArrayList al = new ArrayList();

  for(int i = 0; i < 15 ; i ++) {
   al.add(new Object());
  }
  System.out.println(al.size());
}
}

模拟链表的容器

package com.bjsxt.iterator;

public class LinkedList {

//记录节点的开始位置
Node head = null;
//记录上一次最后一个节点的位置
Node tail = null;
int size = 0;

public void add(Object o) {

  Node n = new Node(o , null);
  if(head == null) { //说明该节点是第一个节点
   head = n;
   tail = n;
  }
  //如果不是第一个节点，，未加该节点之前的最后一个节点的next应该指向新加的节点
  tail.setNext(n);
  //并且此时，，最后一个节点是新加的节点，，所以应该将tail 改成新加的节点 n
  tail = n;
  size ++;
}

public int size () {
  return size;
}
}

接口中所有方法都是public

当考虑想把ArrayList 和 LinkedList 封装起来时

想到了用接口Collection

package com.bjsxt.iterator;

public interface Collection {

void add(Object o) ;
int size();
}

package com.bjsxt.iterator;

import com.bjsxt.iterator.ArrayList;
public class Test {

public static void main(String[] args) {

  LinkedList ll = new LinkedList();


  //面向接口編程   ，，這樣更零活    ，，，如果写在配置文件中会更加的方便
  Collection c = new ArrayList();

  Collection c2 = new LinkedList();
  for(int i = 0; i < 15 ; i ++) {
   c.add(new Cat(i));
  }
  System.out.println(c.size());
}
}

当想到要遍历ArrayList 和 ListedList 时，想到了可以再接口中添加一个方法2 showAll();

package com.bjsxt.iterator;

import com.bjsxt.iterator.Collection;
public class ArrayList implements Collection{

private Object [] objects = new Object[10];
private int index = 0;
public void add (Object o) {
  if(index == objects.length) {
   Object [] newObjects = new Object[objects.length*2];
   System.arraycopy(objects, 0, newObjects, 0, objects.length);
   objects = newObjects;
  }
  objects[index] = o;
  index ++;
}

public int size() {
  return index;
}

public void showAll() {
  for(int i = 0 ; i < index; i++){
   Object b = objects[i];
   System.out.println(b);
  }
}
}

package com.bjsxt.iterator;
import com.bjsxt.iterator.Collection;

public class LinkedList implements Collection{

//记录节点的开始位置
Node head = null;
//记录上一次最后一个节点的位置
Node tail = null;
int size = 0;

public void add(Object o) {

package com.bjsxt.iterator;

public interface Collection {

void add(Object o) ;
int size();
void showAll();
}

还有一种更好的方法：

package com.bjsxt.iterator;

import com.bjsxt.iterator.Collection;
public class ArrayList implements Collection{

private class ArrayListIterator implements Iterator {

  private int currentIndex = 0;
  @Override
  public boolean hasNext() {
   if(currentIndex >= index )
    return false;
   return true;
  }

  @Override
  public Object next() {
   Object tmp = objects[currentIndex];
   currentIndex ++;
   return tmp;
  }

}

}

package com.bjsxt.iterator;
import com.bjsxt.iterator.Collection;

public class LinkedList implements Collection{

//记录节点的开始位置
Node head = null;
//记录上一次最后一个节点的位置
Node tail = null;
int size = 0;

public void add(Object o) {

@Override
public Iterator iterator() {

  return new LinkedListIterator();
}

private class LinkedListIterator implements Iterator {

  Node currentNode = head ;
  @Override
  public boolean hasNext() {

   if(currentNode == null) {
    return false;
   }

   return true;
  }

  @Override
  public Object next() {
   //取到當前的節點
   Object tmp = currentNode;
   //將該節點指針向下移一個
   currentNode = currentNode.getNext();
   return tmp;
  }

}
}

package com.bjsxt.iterator;

public interface Collection {

void add(Object o) ;
int size();
void showAll();

Iterator iterator();
}

package com.bjsxt.iterator;

public interface Iterator {

Object next();
boolean hasNext();
}

package com.bjsxt.iterator;

import com.bjsxt.iterator.ArrayList;
public class Test {

public static void main(String[] args) {

  LinkedList ll = new LinkedList();


  //面向接口編程   ，，這樣更零活
  Collection c = new ArrayList();

  Collection c2 = new LinkedList();
  for(int i = 0; i < 15 ; i ++) {
   c.add(new Cat(i));
  }
  System.out.println(c.size());


  Iterator it = c.iterator();
  while(it.hasNext()) {
   Object o = it.next();
   System.out.println(o + "");
  }
}
}

下面是泛型的一个例子： {泛型有点像C++中的模板}

package com.bjsxt.iterator;

//泛型
public class GenericArrayList<Element> {

private Object [] objects = new Object[10];
private int index = 0;
public void add (Element o) {
  if(index == objects.length) {
   Object [] newObjects = new Object[objects.length*2];
   System.arraycopy(objects, 0, newObjects, 0, objects.length);
   objects = newObjects;
  }
  objects[index] = o;
  index ++;
}

public int size() {
  return index;
}

public static void main(String args[]) {
  GenericArrayList<String> a = new GenericArrayList<String>();
  a.add("String");
}
}