在Java中的方法之间共享变量

Question

I'm new in Java and I have little problem. I want to make array in one method and display in length in other. I know how to to both in one method:

class Test
{
    public void create()
    {
        Scanner in = new Scanner(System.in);
        System.out.println("Number of elements: ");
        int n=in.nextInt();
        int arr[]=new int[n];
        System.out.println("Number of elements: " + arr.length);
    }
}

But how can I do something like this?

class Test
{
    public void create()
    {
        Scanner in = new Scanner(System.in);
        System.out.println("Number of elements: ");
        int n=in.nextInt();
        int arr[]=new int[n];
    }

    public void display()
    {
        System.out.println("Wielkosc tablicy: " + arr.length);
    }
}

Answer 1

Make arr a private instance variable of your class, so that it is accessible from any method:

class Test
{
    private int[] arr;
    public void create()
    {
        Scanner in = new Scanner(System.in);
        System.out.println("Number of elements: ");
        int n=in.nextInt();
        arr=new int[n];
    }

    public void display()
    {
        System.out.println("Wielkosc tablicy: " + arr.length);
    }
}

Answer 2

If the array is only expected to exist within the lifetime of a call to create I'd recommend making display private. Then updating the signature of display to take an int[] as an argument

class Test {
    public void create() {
        Scanner in = new Scanner(System.in);
        System.out.println("Number of elements: ");
        int n=in.nextInt();
        int arr[]=new int[n];
        display(arr);
    }

    private void display(int[] arr) {
        System.out.println("Wielkosc tablicy: " + arr.length);
    }
}

If the int[] is to live for longer than just the call to create then you should make the int[] a field on on Test as mentioned in the answer by @lodo