Why do both Java Objects return the same data

Question

I have created 2 objects of the class GConveyor. I want to get some data about the objects when I select them, but both return the same information. Thanks for the help!

/* 
* File: DragObjects.java  
*/ 
import acm.graphics.*; 
import acm.program.*; 
import java.awt.event.*;

public class DragObjects extends GraphicsProgram { 
private static final long serialVersionUID = 1L;
// Initializes the program 
public void init() { 
    //adding a few test objects
    GConveyor conv = new GConveyor(50, 44, 120); 
    add(conv); 
    GConveyor conv2 = new GConveyor(30, 24, 60); 
    add(conv2); 

    addMouseListeners(); 
    addKeyListeners(); 
    } 

// Called on mouse press to record the coordinates of the click */ 
public void mousePressed(MouseEvent e) { 
    // GPoint has X and Y coordinate 
    last = new GPoint(e.getPoint()); 
    gobj = getElementAt(last);  
    //looking at stuff so to understand
    getObjectData ();
}


public void getObjectData (){
    //looking at stuff so to understand
    System.out.println(gobj.toString());    

    GContainer obLength = gobj.getParent();
    System.out.println(obLength.toString());    

    int d = ((GCompound) gobj).getElementCount();
    System.out.println( "Element per GConveyor:"+ d  );

    System.out.println( "hashcode:" +gobj.hashCode());

    int y = this.getElementCount();
    System.out.println( "this Element Count:"+ y  );

    int a = GConveyor.getBF();      
    System.out.println( "bf:" + a  );
    int b = GConveyor.getEF();      
    System.out.println( "ef:" + b  );
    int h = GConveyor.getLength();      
    System.out.println( "length:" + h  );
    int c = ((GConveyor) gobj).getLength();     
    System.out.println( "length:" + c  );       
}



// Called on mouse drag to reposition the object 
public void mouseDragged(MouseEvent e) { 
    if (gobj != null) { 
        gobj.move(e.getX() - last.getX(), e.getY() - last.getY()); 
        last = new GPoint(e.getPoint());
        } } 

/* Private instance variables */
private GObject gobj; 
/* The object being dragged */
private GPoint last; 

}

the following is my GConveyor class

 /* 
 * 
 * File: GConveyor.java * This class implements a conveyor as a GCompound.
 */ 

import java.awt.Color;
import acm.graphics.*; 

public class GConveyor extends GCompound {
/* Constants specifying frame size*/
private static final int FRAME_WIDTH = 2;
private static int myBf;
private static int myEf;
private static int myLength;

private static final double scale = 10;
/* Private instance variables */
private GRect outer;
private GRect chain_box;
private GRect effWidth;
private GPolygon pti;
private GPolygon pto;

public GConveyor(int bf, int ef, int length) {
outer = new GRect(length, ((FRAME_WIDTH *2) + bf));
chain_box = new GRect(length , bf - ef);
effWidth = new GRect(length, bf);
pti = createAnchor(scale);
pto = createAnchor(scale);
add(outer, 0 , 0);
add(chain_box, 0 , FRAME_WIDTH);
add(effWidth, 0 , FRAME_WIDTH);
add(pti, 0 , FRAME_WIDTH + (bf-ef) + (ef/2));
add(pto, length , FRAME_WIDTH + (bf-ef) + (ef/2));

myBf = bf;
myEf = ef;
myLength = length;

}

public static int getBF(){
return myBf;
}
public static int getEF(){
return myEf; 
}
public static int getLength(){
return myLength;
}


/* Creates a hex for the Anchor */
private GPolygon createAnchor(double scale) {
GPolygon poly = new GPolygon();
poly.addVertex(-0.25*scale, 0.433*scale);
poly.addVertex(-0.5*scale, 0.0*scale);
poly.addVertex(-0.25*scale, -0.433*scale);
poly.addVertex(0.25*scale, -0.433*scale);
poly.addVertex(0.5*scale, 0.0*scale);
poly.addVertex(0.25*scale, 0.433*scale);
poly.setFilled(true);
poly.setFillColor(Color.BLUE);
return poly;
}

public String toString(){
return("" +myBf+ +myEf+ +myLength+ "");

}

}

GConveyor wouldn't be a static class would it?

Scary Wombat
– Scary Wombat

2014-03-06 02:08:05 +00:00
Commented Mar 6, 2014 at 2:08 — Scary Wombat
– Scary Wombat, Commented Mar 6, 2014 at 2:08
I have some static methods

user3386112
– user3386112

2014-03-06 02:14:21 +00:00
Commented Mar 6, 2014 at 2:14 — user3386112
– user3386112, Commented Mar 6, 2014 at 2:14

aliteralmind · Accepted Answer · 2014-03-06 02:20:31Z

2

These variables are static, so these single variables (and their singular values) will be used in all instances of your GConveyor class. That is why you are getting the same information.

private static final int FRAME_WIDTH = 2;
private static int myBf;
private static int myEf;
private static int myLength;

Eliminate the static keyword where you don't need them (where unique information is required in each instance), and you should be good.

edited Mar 6, 2014 at 2:20

answered Mar 6, 2014 at 2:14

aliteralmind

20.2k17 gold badges80 silver badges109 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

ajb Over a year ago

static is probably OK for FRAME_WIDTH. But not the others.

aliteralmind Over a year ago

Yes. true. Leave FRAME_WIDTH as static.

ajb · Accepted Answer · 2014-03-06 02:15:01Z

2

myBF, myEF, and myLength are declared static in GConveyor. That means there is only one of each of those integers, and each one is shared by all objects of the class. When you call the GConveyor constructor to create a second instance, the constructor sets those static fields, which then affect the values returned for the first instance.

answered Mar 6, 2014 at 2:15

ajb

31.8k4 gold badges63 silver badges86 bronze badges

Comments

chiliNUT · Accepted Answer · 2014-03-06 02:14:26Z

1

Your toString() spits out myBf myEf and myLength, all of which are static. That means they are properties of the class itself (of GConveyer), and not of instances of the class (conv and conv2), so when you call an instance's setter method for any of those, you are modifying the same variable.

You have 2 instances, but only 1 class, so you only have 1 set of those variables, not 2.

Do not make them static if you wish them to be attributed to each instance, and not to the class as a whole.

answered Mar 6, 2014 at 2:14

chiliNUT

19.5k14 gold badges72 silver badges116 bronze badges

Collectives™ on Stack Overflow

Why do both Java Objects return the same data

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related