# ArrayList

**Repository Path**: gaohanghang/ArrayList

## Basic Information

- **Project Name**: ArrayList
- **Description**: 手写ArrayList
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2018-03-02
- **Last Updated**: 2020-12-19

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

> MyArraylist.java

```java
package ArrayList;

import java.util.Arrays;

public class MyArraylist {
    private Object[] objs = new Object[10]; //定义数组，初始化长度是10
    private int index = 0; //数组下标

    /**
     * 添加
     *@param o
     */
    public void add(Object o){
        if (index == objs.length){
            // 扩容
            extend();
        }
        objs[index++] =o;
    }

    /**
     * 根据下标获取对象
     * @param index 下标
     * @return
     */
    public Object get(int index){
        return objs[index];
    }

    /**
     * 计算元素个数
     * @return
     */
    public int size(){
        int size = 0;
        for (int i = 0; i < objs.length; i++) {
            if(objs[i]!=null){
                size++;
            }
        }
        return size;
    }

    /**
     * 清空
     */
    public void clear(){
        for (int i = 0; i < objs.length; i++) {
            objs[i] = null;
        }
    }

    /**
     * 判断是否包含
     * @param o
     * @return
     */
    public boolean contains(Object o){
        for (int i = 0; i < objs.length; i++) {
            if(o!=null&&o.equals(objs[i])){
                return true;
            }
        }
        return false;
    }

    /**
     * 根据下标删除
     */
    public void remove(int index){
        if (index<0 || index>= this.size()){
            System.out.println("下标无效，无法删除。。。");
            throw new IndexOutOfBoundsException();
        }
        for (int i = index; i < objs.length; i++) {
            objs[i] = objs[i+1];
            if (i==this.size()){
                break;
            }
        }
    }

    /**
     * 根据对象删除
     * @param o
     */
    public void remove(Object o){
        int index = getIndexByObject(o);
        remove(index);
    }

    /**
     * 根据对象获取对象的下标
     * @return
     */
    public int getIndexByObject(Object o){
        for (int i = 0; i < objs.length; i++) {
            if(o!=null&&o.equals(objs[i])){
                return i;
            }
        }
        return -1;
    }

    /**
     * 自定义迭代器
     */
    public MyIterator iterator(){
        return new Iterator();
    }

    class Iterator implements MyIterator{
        private int size = 0;
        @Override
        public boolean hasNext() {
            if(objs[size]!=null) return true;
            else return false;
        }

        @Override
        public Object next() {
            size++;
            return objs[size-1];
        }
    }




    /**
     * 扩容
     */
    private void extend(){
        Arrays.copyOf(objs,objs.length+1);
    }


}
```

> MyIterator.java

```java
package ArrayList;

/**
 * 自定义迭代器
 *
 */
public interface MyIterator {
    boolean hasNext();
    Object next();
}
```

> Test.java

```java
package ArrayList;

import java.util.ArrayList;

public class Test {
    public static void main(String[] args) {
        ArrayList list = new ArrayList();
        list.add("111");
        list.add("222");
        list.add("333");


//        System.out.println(list.get(0));
//
//        for (int i = 0; i < list.size(); i++) {
//            System.out.println(list.get(i));
//        }
//
//        list.remove(1);
//        for (int i = 0; i < list.size(); i++) {
//            System.out.println(list.get(i));
//        }
//
//        //迭代器遍历
//        System.out.println("迭代器遍历：");
//        Iterator itor = list.iterator();
//        while (itor.hasNext()){
//            System.out.println(itor.next());
//        }

        System.out.println("自定义ArrayList:");
        MyArraylist my = new MyArraylist();
        my.add("aaa");
        my.add("bbb");
        my.add("ccc");
        my.add("ddd");

        System.out.println(my.get(1));
        System.out.println(my.size());

        System.out.println("自定义ArrayList集合for循环：");
        for (int i = 0; i < my.size() ; i++) {
            System.out.println(my.get(i));
        }

//        my.clear();
//        System.out.println("测试清空：");
//        for (int i = 0; i < my.size() ; i++) {
//            System.out.println(my.get(i));
//        }
//        System.out.println("清空后的长度"+my.size());


        System.out.println(my.contains("ccc"));

//        my.remove(4);
//        my.remove("dddd");
        System.out.println("测试删除：");
        for (int i = 0; i < my.size(); i++) {
            System.out.println(my.get(i));
        }

        System.out.println("测试自定义的迭代器");
        MyIterator itor = my.iterator();
        while (itor.hasNext()){
            System.out.println(itor.next());
        }

    }
}
```