Java program behaving strangely

halfpower · 01-24-2012, 08:31 PM

I wrote a java program and it is not behaving as expecting. This is the code:

Code:

public class test{    
    static MyPoint[] p = new MyPoint[3];  
      
    public static void printPoints(){    
        System.out.println( " x = " + p[0].x + " y = " + p[0].y);
        System.out.println( " x = " + p[1].x + " y = " + p[1].y);
        System.out.println( " x = " + p[2].x + " y = " + p[2].y);
    }
       
    public static void main(String[] args) {
        p[0].x = 0.0f;
        p[0].y = 0.0f;        
        p[1].x = 0.12f;
        p[1].y = 0.13f;        
        p[2].x = 0.367878f;
        p[2].y = 0.756785f;        
        printPoints();
    }      
}

class MyPoint{    
    public static float x;
    public static float y;    
}

I would expect the output of this program to be:

Code:

 x = 0.0 y = 0.0
 x = 0.12 y = 0.13
 x = 0.367878 y = 0.756785

But instead, the output is:

Code:

 x = 0.367878 y = 0.756785
 x = 0.367878 y = 0.756785
 x = 0.367878 y = 0.756785

I'm pulling my hair out trying to figure out why this is happening. Does anyone know what it is I'm overlooking?

ntubski · 01-24-2012, 10:28 PM

Code:

class MyPoint{    
    public static float x;
    public static float y;    
}

static means there will be a single copy shared among all objects of the class.

halfpower · 01-25-2012, 12:04 PM

Won't that be okay? Won't "static MyPoint[] p = new MyPoint[3]" create separate instances of MyPoint?

ntubski · 01-25-2012, 12:31 PM

Quote:

Originally Posted by halfpower

Won't "static MyPoint[] p = new MyPoint[3]" create separate instances of MyPoint?

Yes, but

Code:

class MyPoint{    
    public static float x;
    public static float y;    
}

means each MyPoint instance will use the same x and y.