java - 如何在java中使用某些特定索引將值存儲到arraylist中 (how to store value into arraylist with some specific index in java)

問題描述

java ‑ 如何在java中使用某些特定索引將值存儲到arraylist中 (how to store value into arraylist with some specific index in java)

我有價值列表，例如

0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.10, 0.11, 0.12< /p>

我想將它存儲到具有特定索引的 ArrayList 中

0.1, 0.2, 0.3, = = 索引 1

0.4, 0.5, 0.6, == 索引 2

0.7, 0.8, 0.9, == 索引3

0.10, 0.11, 0.12, == 索引 4

謝謝

參考解法

方法 1:

ArrayList[][] array = {{0.1,0.2,0.3},{0.4,0.5,0.6},{0.7,0.8,0.9},{0.10,0.11,0.12}}

This is a multi‑dimensional array

To set values:

array[0][0] = 0.1;
array[0][1] = 0.2;
array[1][0] = 0.4;
array[1][1] = 0.5;

...ect

Also see How to create a Multidimensional ArrayList in Java?

方法 2:

you use array List and HaspMap for you requirement

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

public class Test {

    public static void main(String[] args) {
        ArrayList<Double> list  = new ArrayList<Double>();  
        Map<String, ArrayList<Double>> map = new HashMap<String, ArrayList<Double>>();

        list.add(0.1);
        list.add(0.2);

        map.put("key", list);

        System.out.println(map.get("key").get(0));
    }   
}

方法 3:

In an ArrayList<Double> a single index can have a single value.

If you want to store more than one value try using a ArrayList<ArrayList<Double>>.

If you want to store it in an index use .set(index, value)

ArrayList<Double> list = new ArrayList<>();

list.add(0.1);
list.add(0.2);
list.add(0.3);

ArrayList<ArrayList<Double>> mainList = new ArrayList();

mainList.set(0, list);

From your list I see that 3 values make a list.

double []values = {0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.10, 0.11, 0.12};

ArrayList<ArrayList<Double>> mainList = new ArrayList();
int k = 0;
for(int i = 0; i < values.length; i += 3)
{
  ArrayList<Double> list = new ArrayList();
  list.add(values[i]);
  list.add(values[i + 1]);
  list.add(values[i + 2]);

  mainList.set(k ++, list);
}

方法 4:

In arrayList you can't keep multiple value in same index, it just doesn't work that way.

Based on your requirement, i think, you can design the data structure in two way ‑

1. Map

Map<Integer, List<Double>>

a map keeping index as key, and list of the items as value. Thus keep (1, [0.1, 0.2, 0.3]) means 1 index as key and corresponding list as value

2. List of User Defined Object

class IndexValue {
  int index;
  double value;
  IndexValue(int index, double value) {
     this.index = index;
     this.value = value;
  }
}

List<IndexValue> indexValueList = new ArrayList<>();
indexValueList.add(new IndexValue(1, .1));
indexValueList.add(new IndexValue(1, .2));
indexValueList.add(new IndexValue(1, .3));

(by Putra Nurfajar、JavaFox、Kumaresan Perumal、Uma Kanth、shakhawat)

參考文件

1. how to store value into arraylist with some specific index in java (CC BY‑SA 2.5/3.0/4.0)