有没有办法在 Java 中创建一个空数组，但可以有无限量

Question

I'm working on a program in java that takes all user inputted numbers until -99 with a loop, I am using Arrays but I have no way of knowing how many numbers will be inputted. I'm also a novice with java and I don't know that much. ` import java.util.*; public class ArrayComputing {

public  int[] makeArray()
{
    int[] nums = //where I need help
    int numArray;
    int i =0;
    Scanner input = new Scanner(System.in);
    boolean negative99=false;
    while (negative99==false)
    {
    i++;
    System.out.println("Enter a number");
    numArray= input.nextInt();
    if (numArray==-99)
    {
        break;
    }
    else    
    {
    nums[i]=numArray;
    System.out.println(Arrays.toString(nums));
    }
    
    }
    return nums;
    
    
    
}

} `

Answer 1

If you use List (ArrayList in particular) it will do what you need. It can expand as you add the members to the list and will not run out space. As opposed to Array where you need to allocate space in advance and need to know how many members to expect.

Answer 2

What you're asking for, is a behaviour of Dynamic Array Abstract Data Type, one popular implementation of which, is the ArrayList class in Java .

In the case of raw/built-in new int[]{..} array, Java Specification (and mostly all other languages) require you to allocate a specific segment of the memory, for which, you need to provide a size of the array.

In your case, ArrayList , or LinkedList will help.

Answer 3

An array is a structure of defined size that can, to my knowledge, not directly be extended or reduced in size.

You may however use an ArrayList, which is of undefined size.

ArrayList<Integer> numberList = new ArrayList();

You can then "add" values to it:

numberList.add(value);

The usage of ArrayList may be found here: https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html

You may do so until your computer runs out of ressources to store the values that are contained in the ArrayList.

Answer 4

Unfortunately the length of an array can't be negative. It will throw a NegativeArraySizeException.

Anyway you can first let the user define a length and afterwards you can create one with this size.

    public static  int[] makeArray() {
    
    Scanner input = new Scanner(System.in);
    
    System.out.print("> ");
    int in = input.nextInt();
    int[] nums = new int[in];
    
    int numArray;
    int i =0;
    //...