如何在不同类中的类中操纵数组？

Question

I hava a class, with an array in it. This is the code of the class currently:

public class SomeClass{
     int array[] = new int[3];
     array[0] = 1;
     array[1] = 1;
     array[2] = 1;
}

I want to create a class, that will contain a method. That method sets all the numbers in the array inside SomeClass , equal to 0.

If it was a method inside SomeClass , it would be very easy. I would just add the follwing method to the existing class:

public void manipulateArray(){
     for(int i=0;i<3;i++){
          array[i]=0;
     }
}

But, I want this method to be inside a different class, and manipulate the array inside the class SomeClass .

What would be the most standard way to do this, inside an application? Thanks

Answer 1

You have to set this array field as a public static to access it from outside of the class and modify it:

public class SomeClass {
    public static int array[] = new int[3];
}

And then:

public void manipulateArray(){
     for(int i=0;i<3;i++){
          SomeClass.array[i]=0;
     }
}

Edit:

However this is just quick solution. Better is to create setter/getter for this field and work with objects of this class.. But.. Everything depends on your design.

Answer 2

1. make your array public and access it via SomeClass sc = new SomeClass(); sc.array[0] = 4; SomeClass sc = new SomeClass(); sc.array[0] = 4; Do not do that if you do not have to !

2. make your array static SomeClass.array[0] = 4; Do not do that if you do not have to !

3.leave it private and make public setters getters like

public void setArray(int[] array) {
this.array = array;
}

SomeClass sc = new SomeClass();
sc.setArray(myNewArray);

Actually do that !

Answer 3

Why don't you simply implement getter for the array?

In the other class you can have an object of type SomeClass and get the array from there:

SomeClass someClass = new SomeClass();
int myArr = someClass.getArray();
someClass.modifyArray();

Answer 4

do like this.

Pass the array to OtherClass.manipulateArray(array) and modify it.

class OtherClass{

    public void manipulateArray(int[] array){
       for(int i=0;i<3;i++){
            array[i]=0;
       }
    }
}

Answer 5

You can declare it like this and pass the array as an argument.

public void manipulateArray(int[] array){
     for(int i=0;i<3;i++){
          array[i]=0;
     }
}

Answer 6

I might be getting this wrong, as this answer is missing, but a standard way is to encapsulate the fields and manage object's state via the interface. So in your case you could provide a reference to SomeClass and reset the array by a reference:

public class SomeClass{
     final int array[] = new int[3];

     { Arrays.fill(array, 1); }

     public void manipulateArray(){
         Arrays.fill(array, 0);  
     }     
}

public class OtherClass{
     SomeClass someClass;

     public OtherClass(SomeClass someClass){ this.someClass = someClass;}

     public void reset(){
         someClass.manipulateArray();
     }
}

Answer 7

above answers are true and useful. maybe depending to other parts of your code, declaring the array as "static" be useful, too.

Answer 8

You can use Java reflection to access the array of SomeClass from a different class.

Here is small code for demonstrating it:

public class POC {
    public static void main(String args[]) {
        new POC().run();
    }

    private void run() {
        SomeClass sc = new SomeClass();
        say("BEFORE: ");
        sc.showArray();

        DifferentClass dc = new DifferentClass();
        dc.manipulateArray(sc);

        say("---");
        say("AFTER: ");
        sc.showArray();
    }

    private class SomeClass {
        private int array[];

        public SomeClass() {
            array = new int[3];

            array[0] = 1;
            array[1] = 1;
            array[2] = 1;
        }

        public void showArray() {
            for (int i = 0; i < array.length; i++) {
                say(i + ">" + array[i]);
            }
        }
    }

    private class DifferentClass {
        public void manipulateArray(SomeClass sc) {
            try {
                Field arrayField = sc.getClass().getDeclaredField("array");
                arrayField.setAccessible(true);

                Object array = arrayField.get(sc);
                for (int i = 0; i < Array.getLength(array); i++) {// equivalent to for(int i=0;i<3;i++){
                    Array.set(array, i, 0); // equivalent to array[i]=0;
                }

                arrayField.setAccessible(false);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    private static void say(String msg) {
        System.out.println(msg);
    }
}

OUTPUT

BEFORE: 
0>1
1>1
2>1
---
AFTER: 
0>0
1>0
2>0