List length length() size() 区别与应用

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