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93 lines (88 loc) · 2.22 KB
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package com.lyss.java.util;
/**
* 手写ArrayList
* @author Administrator
*
*/
public class MyArrayList {
//创建一个空数组对象
private static final Object[] EMPTY_ELEMENTDATA = {};
//申明一个临时的数组
transient Object[] elementData;
//默认的初始化长度为10
private static final int DEFAULT_CAPACITY = 10;
//集合的长度
private int size;
//初始化一个空集合，并制定初始化容量
public MyArrayList(int initialCapacity){
//如果初始化长度大于0，则创建一个对象数组
if (initialCapacity>0) {
this.elementData = new Object[initialCapacity];
}else {
//否则置空
this.elementData =EMPTY_ELEMENTDATA;
throw new IllegalArgumentException("集合的初始化长度为"+initialCapacity);
}
}
//默认初始长度是10
public MyArrayList(){
this(10);
}
//定义判断长度方法size()
public int size(){
return size;
}
//判断是否非空
public boolean isEmpty(){
return size == 0;
}
//判断数组是否越界
public void rangeCheck(int index){
if (index<0 || index >=size) {
throw new IndexOutOfBoundsException("数组越界异常，下标为："+index);
}
}
//扩展长度
private void ensureCapacity(){
if (size>=elementData.length) {
Object[] temp = new Object[elementData.length*3/2];
System.arraycopy(elementData, 0, temp, 0, size);
elementData = temp;
}
}
/**
* 增删改查
*/
public void add(Object object){
ensureCapacity();
elementData[size++]=object;
}
public void add(int index,Object object){
rangeCheck(index);
ensureCapacity();
System.arraycopy(elementData, index, elementData, index+1, size-index);
elementData[index] = object;
size++;
}
public Object get(int index) {
rangeCheck(index);
return elementData[index];
}
public Object set(int index, Object obj) {
rangeCheck(index);
Object oldValue = elementData[index];
elementData[index] = obj;
return oldValue;
}
public void remove(int index) {
rangeCheck(index);
ensureCapacity();
System.arraycopy(elementData, index+1, elementData, index, size-index-1);
size--;
}
public static void main(String[] args) {
MyArrayList list = new MyArrayList();
list.add("asdsad");
System.out.println(list.get(0));
}
}