如何在Java中清空数组？

Question

我正在开发一个使用部分填充数组的项目。我在使用空方法时遇到问题。目的是清空一个数组，因此数组的大小应该为零。相反，我的方法将数组的元素更改为等于 0。如果我要打印数组的大小，它会给我一个非 0 的数字。我该如何解决这个问题？

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.Arrays;

public class IntBag {
    private int capacity;
    private String fileName;
    private int[] bag;

    public void intBag() {

    }

    public void intBag(int capacity) {
        capacity = this.capacity;
    }

    public void intBag(IntBag other) {
        other.capacity = this.capacity;
        other.fileName = this.fileName;
        other.bag = this.bag;
    }

    public void empty() {
        Arrays.fill(bag, 0);
    }

    public static void main(String[] args) throws FileNotFoundException {
        Scanner input = new Scanner(System.in);
        IntBag intBag = new IntBag();
        int[] bag = new int[20];
        intBag.bag = bag;
        boolean done = false;

        while (!done) {
            System.out.println(Arrays.toString(bag));
            System.out.println("1. Add an Item to the Array");
            System.out.println("2. Replace an Item in the Array");
            System.out.println("3. Replace every item in the Array");
            System.out.println("4. Look for an Item in the Array");
            System.out.println("5. Delete an Item in the Array");
            System.out.println("6. Delete all Items in the Array");
            System.out.println("7. Size of Array");
            System.out.println("8. Empty the Array");
            System.out.println("9. Print the Array");
            System.out.println("10. Change Length of Array");
            System.out.println("11. toString");
            System.out.println("12. toStringDescending");
            switch (input.nextInt()) {
            case 1:
                System.out.println(Arrays.toString(bag));
                System.out.println("Add an Item to the Array");
                intBag.add(input.nextInt());
                break;
            case 2:
                System.out.println(Arrays.toString(bag));
                System.out.println("Replace an Item in the Array");
                intBag.replace(input.nextInt(), input.nextInt());
                break;
            case 3:
                System.out.println(Arrays.toString(bag));
                System.out.println("Replace every item in the Array");
                intBag.replaceAll(input.nextInt(), input.nextInt());
                break;
            case 4:
                System.out.println(Arrays.toString(bag));
                System.out.println("Look for an Item in Array");
                intBag.contains(input.nextInt());
                break;
            case 5:
                System.out.println(Arrays.toString(bag));
                System.out.println("Delete an Item in the Array");
                intBag.delete(input.nextInt());
                break;
            case 6:
                System.out.println(Arrays.toString(bag));
                System.out.println("Delete all Items in the Array");
                intBag.deleteAll(input.nextInt());
                break;
            case 7:
                System.out.println("Size of Array: " + intBag.size());
                break;
            case 8:
                System.out.println("Empty the Array");
                intBag.empty();
                break;
            case 9:
                System.out.println("Print the Array");
                intBag.toArray();
                break;
            case 10:
                System.out.println("Change Length of Array");
                intBag.changeCapacity(input.nextInt());
                break;
            case 11:
                System.out.println("toString");
                intBag.toString();
                break;
            case 12:
                System.out.println("toStringDescending");
                intBag.toStringDescending();
                break;
            }

        }
    }

}

Answer 1

既然你说你不能使用 ArrayLists，那么使用普通数组的一种方法就是简单地重新声明变量。

int[] test = new int[4];
System.out.println(test.length);
test = new int[0];
System.out.println(test.length);
//prints 4 and 0

如果您想重新扩展数组大小，您可以使用类似这样的方法来创建该数组以执行上述操作。

public static int[] resizeArray(int[] oldArray, int newSize){
    int[] newArray = new int[newSize];
    for(int i=0; i<newArray.length && i<oldArray.length; i++){
        newArray[i]=oldArray[i];
    }
return newArray;
}

Answer 2

Java 数组大小是一个固定数量。即一旦定义，就无法更改。您可能想要使用 ArrayList，因为您可以更改大小。

这是一个清空数组的示例方法：

public void emptyList(ArrayList<Integer> bag){
    for(int i=bag.size()-1; i>=0; i--){
        bag.remove(i);
    }
}