package com.byd.cn;import java.util.ArrayList;import java.util.List;import org.apache.catalina.User;public class TestArryList {public static void main(String[] args) {//java中的length属性是针对数组,数组的长度则用到了length这个属性.String[] list = {"12","12","12"};//java中的length()方法是针对字符串String说的,如果想看这个字符串的长度则用到length()这个方法.String a = "123232";//java中的size()方法是针对泛型集合说的,如果想看这个泛型有多少个元素,就调用此方法来查看!List<Object> array=new ArrayList<Object>();array.add(a);System.out.println("length:"+list.length+"<<==>>length():"+a.length()+"《《《Size():"+array.size());List<User> list1 = new ArrayList<User>(); if (list1 != null) { System.out.println(list1.size() + "1"); } if (list1.size() > 0) { System.out.println("2"); } if (null == list1) { System.out.println("3"); } if (list1.size() == 0) { System.out.println("4"); } if (list1 != null && list1.size() == 0) { System.out.println("test list==0"); } if (list1 != null && list1.size() > 0) { System.out.println("test list>0"); } List<User> list2 = null; System.out.println(list2 + "==>list2=null");}}
输出结果：
length:3<<>>length():6《《《Size():1
01
4
test list0
null==>list2=null