如何在 Java 中调整数组的大小？

Question

I have to write a method that inserts an integer into an already sorted integer array and another that removes an integer from that array. Then I have to print out that same array. Is is possible to make an array one element longer or shorter in Java?

The code shown is the example from my homework.

public static void main(String[] args){
    int[] a1 = {-8,-5,-3,0, 3, 7, 10, 12,15, 22};
    System.out.println(Arrays.toString(a1));
    addInt(a1, 2);
    System.out.println(Arrays.toString(a1));
    addInt(a1, 13);
    System.out.println(Arrays.toString(a1));
    removeInt(a1,-5);
    System.out.println(Arrays.toString(a1));
    removeInt(a1, 10);
    System.out.println(Arrays.toString(a1));
    System.out.print(getInt(a1, 2));    //should output 0
}

I've tried setting my new array to the original array, a1, in my addInt method but when I run it, it just prints out the unmodified array. I'm not allowed to use ArrayList.

Edit: Resolved. The assignment was made impossible on purpose as an exercise leading up to our introduction of ArrayList.

Answer 1

Guessing you wrote addInt something like this:

void addInt(int[] a, int n){
    int[] newArray = new int[a.length+1];
    System.arraycopy(a, 0, newArray, 0, a.length);
    newArray[a.length] = n;
    a = newArray;        // WRONG!
}

Method parameters in Java are passed by value , which basically means that a in addInt and a1 in the call addInt(a1, 2) are two separate variables. Upon entry into addInt , a initially refers to the same array as a1 but beyond that there is no further relationship between a and a1 , and subsequently changing a to refer to something else has no effect on a1 .

Your only option is to change addInt so that it returns the new array as a function result:

int[] addInt(int[] a, int n){
    int[] newArray = new int[a.length+1];
    System.arraycopy(a, 0, newArray, 0, a.length);
    newArray[a.length] = n;
    return newArray;
}

and then call it like this:

a1 = addInt(a1, 2);

Answer 2

You can't modify the array length. when you create an array like int[] fixedLEngthArray = new int[n] you bassically reserved memory for n ints. if you need n+1 wou will have to create a new array into which to copy the old one and insert/remove the element.