ArrayList,数组中的存储类型

package com.web;

import java.util.ArrayList;

public class Test39 {
    
    
    public static void main(String[] args) {
    
    
        ArrayList arrayList = new ArrayList();
        arrayList.add("a");
        arrayList.add('c');
        arrayList.add(true);
        arrayList.add(5);
        System.out.println(arrayList);//[a, c, true, 5]各种类型都可以存进去,但取出来时容易报错，用泛型<>事先指定类型

        double[] arr = new double[4];
        arr[0]= 1.2;
        arr[1]=1;
        arr[2]=2;
        for (int i = 0; i < arr.length; i++) {
    
    
            System.out.println(arr[i]);
             //1.2
            //1.0
            //2.0
            //0.0 默认加上去的
        }
        boolean[] arr2 = {
    
    true,false,true,true};
        for (boolean b : arr2) {
    
    
            System.out.println(b);
        }
        //true
        //false
        //true
        //true
        Object[] arr3 = {
    
    new Object(),new Object(),new Object()};
        for (int i = 0; i < arr3.length; i++) {
    
    
            System.out.println(arr[i]);
        }//不知道为啥输出了数字
        //1.2
        //1.0
        //2.0
    }
}