js数组和list和map基础用法

说明:最近接触到一些js的功能代码，然后发现很多基础都不会弄，
尤其是涉及到数据处理的，java里面常用的数组 ，list ，map，转到js里面，就完全搞不明白，一头雾水，非常影响工作效率，
因此弄了这个小demo，用来记录一下js里面的常用处理数据的一些工具类写法。

js篇
step1: map的基本用法

import {Component, OnInit} from '@angular/core';

@Component({
  selector: 'app-user',
  standalone: true,
  imports: [],
  templateUrl: './user.component.html',
  styleUrl: './user.component.css'
})
export class UserComponent implements OnInit{


  constructor() {
    console.log('constructor')
  }

  ngOnInit(): void {
    console.log('ngOnInit')

    name.set('a', 1);
    name.set('b', 2);
    name.set('c', 3);


    console.log(name);

    console.log(name.get('a'));

    name.set('a', 97);
    console.log(name.get('a'));

    console.log(name);

    console.log(name.size);

    name.delete('b');
    console.log(name);

    console.log(name.size);

  }

}


var name = new Map();

step2: js数组的基本用法，相当于java的arraylist，只不过js里面的数组非常的随意，或者叫自由，数组里基本啥都能装，什么乱起八糟的都能往里面塞，也没有固定长度，对于那些写惯了java的人看来，这很离谱

import {Component, OnInit} from '@angular/core';

@Component({
  selector: 'app-user',
  standalone: true,
  imports: [],
  templateUrl: './user.component.html',
  styleUrl: './user.component.css'
})
export class UserComponent implements OnInit{


  constructor() {
    console.log('constructor')
  }

  ngOnInit(): void {

    console.log('ngOnInit')

    console.log(mycars)
    console.log(mycars2)

    var name=mycars2[2];  //获取 修改

    mycars2[0]="Opel";


    console.log(name)

    console.log(mycars2)


    console.log(apples)

    console.log(apples2)
    console.log(apples3)



    var bannale =  mycars2[3]

    console.log(bannale)


    mycars2[4] = "无解"
    console.log(mycars2)

    myArray = myArray.filter(item => item !== "banana");
    console.log(myArray); // ["apple", "orange", "grape"]

    mycars2 =   myArray

    console.log(myArray)

    myArray.push('测试数据')
    console.log(myArray)

  }

}


var mycars = new Array();
mycars[0] = "Saab";
mycars[1] = "Volvo";
mycars[2] = "BMW";

var mycars2=new Array("Saab","Volvo","BMW","奥迪");



var apples= new Array()

var size=10

var apples2 = new Array(size)



var apples3 = new Array(1,2,3,4)


let myArray = ["apple", "banana", "orange", "grape", "bananas", "grape", "bananas"];

=我是分割线====
java篇章
step1: java数组

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Num {
    public static void main(String[] args) {
        double[] myList;         // 首选的方法
        double myList2[];         //  效果相同，但不是首选方法
        myList = new double[8];
        double[] arrayRefVar = new double[10];
        double[] arrayRefVar2 = {1, 2, 3, 4};
        arrayRefVar[0] = 5.6;
        arrayRefVar[1] = 4.5;
        arrayRefVar[2] = 3.3;
        arrayRefVar[3] = 13.2;
        arrayRefVar[4] = 4.0;
        arrayRefVar[5] = 34.33;
        arrayRefVar[6] = 34.0;
        arrayRefVar[7] = 45.45;
        arrayRefVar[8] = 99.993;
        arrayRefVar[9] = 11123;

        System.out.println("arrayRefVar数组："+ Arrays.toString(arrayRefVar));
        System.out.println("arrayRefVar2数组："+Arrays.toString(arrayRefVar2));

        // 打印所有数组元素
        for (int i = 0; i < arrayRefVar.length; i++) {
            System.out.println(arrayRefVar[i] + " ");
        }
        // 计算所有元素的总和
        double total = 0;
        for (int i = 0; i < arrayRefVar.length; i++) {
            total += arrayRefVar[i];
        }
        System.out.println("数组总和：" + total);
        // 查找最大元素
        double max = arrayRefVar[0];
        for (int i = 1; i < arrayRefVar.length; i++) {
            if (arrayRefVar[i] > max) {
                max = arrayRefVar[i];
            }
        }
        System.out.println("最大值为： " + max);


    }
}

step2: java 使用arraylist

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Lists {
    public static void main(String[] args) {
        ArrayList<String> sites = new ArrayList<String>();
        sites.add("Google");
        sites.add("Runoob");
        sites.add("Taobao");
        sites.add("Weibo");


        // sites.clear(); 清除所有元素

        int si = sites.size();

        String name = sites.get(0);

        sites.add("韩工");

        sites.remove(0);



        System.out.println(name);

        System.out.println(si);

        System.out.println(sites);
    }
}

step3: java 使用hashmap

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;

public class Mpas {
    public static void main(String[] args) {

        // 创建 HashMap 对象 Sites
        HashMap<Integer, String> maps = new HashMap<Integer, String>();
        // 添加键值对
        maps.put(1, "Google");
        maps.put(2, "Runoob");
        maps.put(3, "Taobao");
        maps.put(4, "Zhihu");


        // maps.clear(); 清除所有


        int si = maps.size();

        String name = maps.get(3);

        boolean isNum = maps.isEmpty();

        System.out.println(isNum);

        System.out.println(name);
        System.out.println(si);
        System.out.println(maps);

    }
}

end