list集合深入理解

list集合常用操作

package com.gcx.demo;import java.util.ArrayList;import java.util.Date;import java.util.List;public class Test2 {public static void main(String[] args) {List list=new ArrayList();// Collection list=new ArrayList(); Collection无序,不能使用带顺序的方法list.add("aaa");list.add("aaa");list.add(new Date());list.add(1234);//jdk1.5自动装箱System.out.println(list.size());list.remove("aaa");//只会删除第一个 底层用return 两个作用:1.方法的返回值 2.结束运行System.out.println(list.size());Object object = list.get(0);//拿到第一个,底层是数组，下标0开始System.out.println(object);list.set(1, "gcx");//把索引为1的值替换掉System.out.println(list.size());}}

简单list底层实现，更加深入的理解

package com.gcx.demo2;public class Demo1 {private Object[] elementData;private int size;/** * 返回个数 * @return */public int size(){return size;}/** * 调用重载构造器 */public Demo1(){this(10);}/** * 初始化容器 * @param initialCapacity */public Demo1(int initialCapacity){if(initialCapacity<0 try="" throw="" new="" exception="" catch="" exception="" e="" e="" printstacktrace="" this="" elementdata="new" object="" initialcapacity="" param="" obj="" public="" void="" add="" object="" obj="" ensurecapacity="" elementdata="" size="" obj="" return="" public="" boolean="" isempty="" return="" size="=0;" param="" index="" return="" public="" object="" get="" int="" index="" rangecheck="" index="" return="" elementdata="" index="" param="" index="" public="" void="" remove="" int="" index="" rangecheck="" index="" int="" nummoved="size-index-1;" if="" nummoved="">0){ System.arraycopy(elementData, index+1, elementData, index, numMoved); } elementData[--size]=null;}/** * 检查是否越界 * @param index */public void RangeCheck(int index){if(index>=size){try {throw new Exception();} catch (Exception e) {e.printStackTrace();}}}/** * 删除对象 * @param obj */public void remove(Object obj){for(int i=0;i<size;i++){if(get(i).equals(obj)){remove(i);}}}/** * 把指定索引的值替换掉 * @param index * @param obj * @return */public Object set(int index,Object obj){RangeCheck(index);Object object = elementData[index];elementData[index]=obj;return object;}/** * 在指定索引处添加值 * @param index * @param obj */public void add(int index,Object obj){RangeCheck(index);ensureCapacity();System.arraycopy(elementData, index, elementData, index+1, size-index);elementData[index]=obj;size++;}/** * 数组扩容 */public void ensureCapacity(){if(size==elementData.length){Object[] newArray=new Object[size*2+1];System.arraycopy(elementData, 0, newArray, 0, elementData.length);elementData=newArray;}}public static void main(String[] args) {Demo1 d=new Demo1(3);d.add("333");d.add("333");d.add("444");d.add("555");System.out.println(d.size());Object object = d.get(3);System.out.println(object);}} </0>