如何先声明数组指针，然后在java中初始化

Question

When I want to use an array for storing the inputs from Scanner, but don't know how many tokens it contain, aren't there any ways to get all the inputs stored in the array with the exact same size as the tokens?

The situation is like this.

    public static void main(String[] args){
         Scanner sc = new Scanner(System.in);

         int[] arr; // just declare not initialize
         int i = 0;


         while(sc.hasNextInt()){
                 arr[i++] = sc.nextInt(); // of course it would cause an error, 
                                          // but as I don't know how many tokens it has,
                                          // I can't initialize like 
                                          // int[] arr = new int[number of tokens] 
         } 
    }

In this situation, I declared some array pointer first, arr, but didn't know the size of the tokens so I couldn't initialize it. Instead I was looking for the ways - making the pointer first, then storing all the data, and then the original pointer pointing the arrays of inputs-stored-array.

Wouldn't there be any ways for this?

Answer 1

When you are not sure of the size of array you need you can use java.util.ArrayList instead of array . ArrayList internally consists of an array and a logic for resizing it based on need. Please refer the below code for your reference :

import java.util.*;

public static void main(String[] args){
     Scanner sc = new Scanner(System.in);

     List<Integer> arrList = new ArrayList<>(); // No need to specify size
     int i = 0;
     while(sc.hasNextInt()){
             arrList.add(sc.nextInt()); // it will take care of resizing the array internally based on the inputs
     } 
}