Save random array for use in entire app

Question

I am very new in java. I have a class that makes a random array with this code.

public class game {
    private int max = 32;
    private int min = 1;
    private Random r = new Random();
    private Integer[] words_Image = new Integer[10];
    public void setwords_Image(Integer[] words_Image) {
        this.words_Image = words_Image;
        for (int i = 0; i < words_Image.length; i++) {
            int num = r.nextInt(max - min + 1) + min;
            int j = 0;
            while (j < i) {
                if (words_Image[j] == num) {
                    num = r.nextInt(max - min + 1) + min;
                    j = -1;
                }
                j += 1;
            }
            words_Image[i] = num;

        }

    }

    public Integer[] getWords_Image() {
        setwords_Image(words_Image);
        return words_Image;
    }
}

I want to make the array just once, then use the array in entire app while array remains constant. I don't know how to do that because when I make an object from that class this array changed each time. Can anyone help me?

Answer 1

"because when i make an object from that class this array changed each time" - you need to know about the static keyword in java.

Static Variables: In Java, variables can be declared with the static keyword. An example is given below.

static int y = 0;

When a variable is declared with the keyword static, its called a class variable. All instances share the same copy of the variable. A class variable can be accessed directly with the class, without the need to create a instance.

Without the static keyword, it’s called instance variable, and each instance of the class has its own copy of the variable.

• It is a variable which belongs to the class and not to object(instance)

• Static variables are initialized only once , at the start of the execution. These variables will be initialized first, before the initialization of any instance variables.

• A single copy to be shared by all instances of the class.

• A static variable can be accessed directly by the class name and doesn’t need any object

Syntax : <class-name>.<variable-name>

Read the article on Static Methods, Variables, Static Block and Class with Example to know more in detail.

Edit: I wanted you to explore and solve it of your own but since you are struggling, i am adding a solution. Note that, you can achieve what you want in many ways.

class Game {

    private static final int max = 32;
    private static final int min = 1;
    private static final Integer[] words_Image = new Integer[10];

    static {
        setwords_Image();
    }

    private static void setwords_Image() {
        Random r = new Random();
        for (int i = 0; i < words_Image.length; i++) {
            int num = r.nextInt(max - min + 1) + min;
            int j = 0;
            while (j < i) {
                if (words_Image[j] == num) {
                    num = r.nextInt(max - min + 1) + min;
                    j = -1;
                }
                j += 1;
            }
            words_Image[i] = num;
        }
    }

    public Integer[] getWords_Image() {
        return words_Image;
    }
}

public class test {

    public static void main(String[] args) {
        Game g1 = new Game();
        System.out.println(Arrays.toString(g1.getWords_Image()));
        Game g2 = new Game();
        System.out.println(Arrays.toString(g2.getWords_Image()));
    }
}

It outputs: (as you expect)

[1, 32, 18, 20, 27, 8, 9, 31, 3, 19]
[1, 32, 18, 20, 27, 8, 9, 31, 3, 19]

Answer 2

What you really need is a singleton. This is a well known concept in programming, best known from the description in Gamma et al.: Design Patterns, popularly known as the Gang of Four book. You should take a look at the discussions in What is an efficient way to implement a singleton pattern in Java?. The two top answers both advocate an enum for implementing the singleton in Java, while other options are also mentioned in the answers. In your case an enum may look like this:

public enum Game {
    INSTANCE;

    private int max = 32;
    private int min = 1;
    private int size = 10;
    private final int[] wordsImage;

    private Game() {
        wordsImage = new int[size];
        Random r = new Random();
        for (int i = 0; i < wordsImage.length; i++) {
            int num = r.nextInt(max - min + 1) + min;
            int j = 0;
            while (j < i) {
                if (wordsImage[j] == num) {
                    num = r.nextInt(max - min + 1) + min;
                    j = -1;
                }
                j += 1;
            }
            wordsImage[i] = num;
        }
    }

    public int[] getWordsImage() {
        return wordsImage;
    }
}

Classes that need to access the random array do for instance:

    System.out.println(Arrays.toString(Game.INSTANCE.getWordsImage()));

If you want to prevent code that uses the array from putting other numbers in it, return only a copy to callers:

    return Arrays.copyOf(wordsImage, size);