How to get the same instance of a class in Java?

Question

Good morning,

I have one little problem. I created one class named Map(). In this class there in one method that generate an Array. Then i created other two classes (Top and Bottom) that extend Map. Then I created 2 objects. One of Top and one of Bottom. I want to get the same array for the Top's object and for the Bottom's object. Here is the code Source:

public class Map{
    public Map(){}

    public int [] yTopValues()
    {
        int [] arrayTopY = new int[100];
        for(int i=0;i<100;i++)
            arrayTopY[i]=randomInt(-50,50);//it puts in i-th position an int between 50 and -50
        return arrayTopY;
    }

    public int [] yBottomValues()
    {
        int [] arrayBottomY = yTopValues;
        for(int i=0;i<100;i++)
            arrayBottomY[i]=arrayBottomY[i]-250;
        return arrayBottomY;
    }

    public int [] xValues()
    {
        int [] arrayX = new int[100];
        for(int i=0;i<100;i++)
            arrayX[i]=randomInt(0,50);//it puts in i-th position an int between 0 and 50
        return arrayX;
    }
//other stuff
}


public class TopMap extends Map{

    public TopMap(){
        this.area=new Area(new Polygon(
            this.xValues,
            this.yTopValues,
            200)            
    );
    }

public class BottomMap extends Map{

    public BottomMap(){
        this.area=new Area(new Polygon(
            this.xValues,
            this.yBottomValues,
            200)            
    );
    }

In the View class I created two objects one of TopMap and one of BottomMap then I drew the areas with g2.draw(topMap.area) and g2.draw(bottomMap.area)

I need the 2 polygons to be similar, but both of them are different because the method is executed twice. What should I do? Thank you very much!!

Answer 1

The class Map does not hold the array. It is local only to the xValues() method. If you want the other classes to get that exact array do this:

/*
 * Since this is a variable in the CLASS field, this object will
 * be accessible to the child class.
 */
private int[] arrayX = new int[100];

public Map(){
     createArrayX(); // This makes sure that the array is created, or else
     // every value inside of it will be 0.
}

public void createArrayX(){ // Exact same thing as xValues(), but without the return type
     for(int i=0;i<100;i++){
        arrayX[i]=randomInt(0,50);
     }
}

public int[] getArrayX(){ // The method that gets the array.
     return arrayX;
}