Thread: Translating old program to java

Ok so this is a personal project. I had made a QBasic program years ago and now i am translating it to be a java applet so I can show it off. I found a book on java programming and went through it completely before I started. I've got it down to just 7 errors.

Here is the code:

/* 
  StarScape Applet By Jon Crawford
  first Java tranlastion
 
*/
 
import java.util.*;
import java.util.Random;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class StarScape extends JApplet {
  public void paint(Graphics g){
    int maxStars = 200, starSpeed = 2, starRadius = 1, speedA;
    int v, w, c, l;
    int stars[][] = new int[maxStars][7];
    setBackground(Color.black);
    do {
      for(int ctrl = 0; ctrl < maxStars; ctrl++) {
        //if star is out of range, and all of them are at start,
        //erase last star position, and give star a new random start
        if( stars[ctrl][1] <= 1 || stars[ctrl][2] <= 1 || stars[ctrl][1] >= 799 || stars[ctrl][2] >= 599) {
          g.setColor(Color.black);
          g.drawOval(stars[ctrl][1], stars[ctrl][2], starRadius, starRadius);
          Random rand = new Random();
          //start in small box in center
          v = rand.nextInt(200) - 99;
          w = rand.nextInt(200) - 99;
          if (v == 0) {
            v = 1;
          }
          if (w == 0) {
            w = 1;
          }
          //random color variable, specifies which of the three layers this star is in.
          //white = front, light grey = middle layer, dark grey = back layer
          c = rand.nextInt(3);
          stars[ctrl][7] = c;
          //adjust values to big box
          stars[ctrl][1] = v + 399;
          stars[ctrl][2] = w + 299;
          stars[ctrl][5] = starRadius;
          stars[ctrl][6] = rand.nextInt(10);
          //get angle
          //first error, these have been declared integers, yet compiler says "precision loss, these are doubles"? 
          l = Math.sqrt((v * v)+(w * w));
          //adjust speed acording to color/layer
          switch (stars[ctrl][7]) {
            case 3:
              speedA = starSpeed;
              break;
            case 2:
              speedA = starSpeed / 4;
              break;
            case 1:
              speedA = starSpeed / 2;
              break;
            default:
              speedA = starSpeed;
          }//end case
          //calculate new star position from old star position
          stars[ctrl][3] = v / l * speedA;
          stars[ctrl][4] = w / l * speedA;
        }//end if
        //erase old star
        g.setColor(Color.black);
        g.drawOval(stars[ctrl][1], stars[ctrl][2], starRadius, starRadius);
        //set old position to new position
        stars[ctrl][1] = stars[ctrl][1] + stars[ctrl][3];
        stars[ctrl][2] = stars[ctrl][2] + stars[ctrl][4];
        stars[ctrl][6] = stars[ctrl][6] + 1;
        //stars get faster as they get closer every 15 steps
        if (stars[ctrl][6] / 15 == (int)(stars[ctrl][6] / 15) && stars[ctrl][5] < 5) {
          stars[ctrl][5] = stars[ctrl][5] + 1;
        }
        //use color/layer number to set the color
        switch (stars[ctrl][7]) {
          case 1:
            g.setColor(Color.white);
            break;
          case 2:
            g.setColor(Color.lightGray);
            break;
          case 3:
            g.setColor(Color.darkGray);
            break;
        }//end case
        //draw new Star
        g.drawOval(stars[ctrl][1], stars[ctrl][2], starRadius, starRadius);
      }//end for
    //check for key press
    //this is not working either
    keyCode = kE.getKeyText(kE.getKeyCode());
    }while (keyCode.equalsIgnoreCase ("")); //continue until a key is pressed
  }//end class
}//end Starscape

I have also comment the sections where errors are found. Please help I am getting frustrated.

EDIT: one error fixed, code updated to reflect fix.

It would be easier if your copied and pasted the full and exact error message separately and not embed what you think the error message says in the middle of your code so we have to hunt them down.

//stars get faster as they get closer every 15 steps
//compiler says a lot of errors on this line, including "symbol not found, method parseInt(Int) not found"
if (stars[ctrl][6] / 15 = Integer.parseInt(stars[ctrl][6] / 15)

You have two problems on this line. The stars array holds int values so why are you trying to parseInt them? One equals sign is assingment. Two equals sign is equality.

Originally Posted by Spidey1980

for ex: 20/15 <> 20/15 with no decimals, however 30/15 == 30/15 with no decimals.

If you are talking about 9 / 2 gives 4 and not 4.5 that is because you are doing integer division and the result will be an integer. If you want a floating point result then you will need to do floating point division instead. Cast at least one value to a double or float.

how can I copy and paste from CMD promt?

In the top left hand corner is a small icon. Left click on that and go to the edit submenu.

The Errors:

 
C:\JSource\Chapter02>javac StarScape.java
StarScape.java:46: possible loss of precision
found   : double
required: int
          l = Math.sqrt((v * v)+(w * w));
                       ^
StarScape.java:92: cannot find symbol
symbol  : variable keyCode
location: class StarScape
    keyCode = kE.getKeyText(kE.getKeyCode());
    ^
StarScape.java:92: cannot find symbol
symbol  : variable kE
location: class StarScape
    keyCode = kE.getKeyText(kE.getKeyCode());
                            ^
StarScape.java:92: cannot find symbol
symbol  : variable kE
location: class StarScape
    keyCode = kE.getKeyText(kE.getKeyCode());
              ^
StarScape.java:93: cannot find symbol
symbol  : variable keyCode
location: class StarScape
  }while (keyCode.equalsIgnoreCase ("")); //continue until a key is pressed
          ^
5 errors
 
C:\JSource\Chapter02>

EDIT: one error fixed, now removed from list

Next issue. I've declared l, v, and w as integers. But the compiler says that they are doubles and need to be integers. This one is really confusing.

And if anyone could tell me a better way to check for a key press it would be greatly appreciated. I want the Applet to run until a key is pressed.

Edit: took out junk, made it simple

possible loss of precision

The return value of the Math.sqrt method is a double. You are trying to assign it to an int. This means that if the method returns 1.5 and you cram it into an int it can only store 1 and the 0.5 is lost.

All other errors are due to you trying to use a variable that has not been declared or you declared it in the wrong scope.

Thank you! adding (int) before Math.sqrt() fixed that one. Still having trouble with the key press checker.

I got it to compile after commenting out the key checker. Guess CTRL ^C will have to do for now

here it is, this will compile, but output using AppletViewer nor via html is not as expected.
note: my resolution is high, so that's why I have this to be 800x600.

 
/* 
  StarScape Applet By Jon Crawford
  first Java tranlastion
 
*/
 
import java.util.*;
import java.util.Random;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class StarScape extends JApplet {
  public void paint(Graphics g){
    int maxStars = 200, starSpeed = 2, starRadius = 1, speedA;
    int v, w, c, l;
    int stars[][] = new int[maxStars+1][8];
    String i = "";
    setBackground(Color.black);
    do {
      for(int ctrl = 0; ctrl < maxStars; ctrl++) {
        //if star is out of range, and all of them are at start,
        //erase last star position, and give star a new random start
        if( stars[ctrl][1] <= 1 || stars[ctrl][2] <= 1 || stars[ctrl][1] >= 799 || stars[ctrl]
 
[2] >= 599) {
          g.setColor(Color.black);
          g.drawOval(stars[ctrl][1], stars[ctrl][2], starRadius, starRadius);
          Random rand = new Random();
          //start in small box in center
          v = rand.nextInt(200) - 99;
          w = rand.nextInt(200) - 99;
          if (v == 0) {
            v = 1;
          }
          if (w == 0) {
            w = 1;
          }
          //random color variable, specifies which of the three layers this star is in.
          //white = front, light grey = middle layer, dark grey = back layer
          c = rand.nextInt(3);
          stars[ctrl][7] = c;
          //adjust values to big box
          stars[ctrl][1] = v + 399;
          stars[ctrl][2] = w + 299;
          stars[ctrl][5] = starRadius;
          stars[ctrl][6] = rand.nextInt(10);
          //get angle
          l = (int)(Math.sqrt((v * v)+(w * w)));
          //adjust speed acording to color/layer
          switch (stars[ctrl][7]) {
            case 3:
              speedA = starSpeed;
              break;
            case 2:
              speedA = starSpeed / 4;
              break;
            case 1:
              speedA = starSpeed / 2;
              break;
            default:
              speedA = starSpeed;
          }//end case
          //calculate new star position from old star position
          stars[ctrl][3] = v / l * speedA;
          stars[ctrl][4] = w / l * speedA;
        }//end if
        //erase old star
        g.setColor(Color.black);
        g.drawOval(stars[ctrl][1], stars[ctrl][2], starRadius, starRadius);
        //set old position to new position
        stars[ctrl][1] = stars[ctrl][1] + stars[ctrl][3];
        stars[ctrl][2] = stars[ctrl][2] + stars[ctrl][4];
        stars[ctrl][6] = stars[ctrl][6] + 1;
        //stars get faster as they get closer every 15 steps
        if (stars[ctrl][6] / 15 == (int)(stars[ctrl][6] / 15) && stars[ctrl][5] < 5) {
          stars[ctrl][5] = stars[ctrl][5] + 1;
        }
        //use color/layer number to set the color
        switch (stars[ctrl][7]) {
          case 1:
            g.setColor(Color.white);
            break;
          case 2:
            g.setColor(Color.lightGray);
            break;
          case 3:
            g.setColor(Color.darkGray);
            break;
        }//end case
        //draw new Star
        g.drawOval(stars[ctrl][1], stars[ctrl][2], starRadius, starRadius);
      }//end for
      //check for key press
      //i = i + e.getKeyChar();
    }while (i == "");
  }//end paint
}//end Stascape

StarScape.html:

<html>
	<head>
		<title>StarScape Applet</title>
	</head>
	<body>
		<h1 align=center>StarScape Applet</h1>
		<center>
			<applet name="StarScape" 
				code="StarScape.class" 
				width=800 
				height=600>
			</applet>
		</center>
	</body>
</html>

And here is the original Qbasic code, this reads variables from a text file (maxStars, start size or radius, and start speed) these have been hard coded in the java code:

'Starscape by Jon Crawford
'Starscap.txt format is variablle to set
'on one line and the value on the next
'line. Variables can go in any order.
 
REM $INCLUDE: 'future.bi'
 
OPEN "I", 1, "starscap.txt"
FOR c = 1 TO 3
	INPUT #1, B$
	IF B$ = "maxstars" THEN INPUT #1, maxstars
	IF B$ = "speed" THEN INPUT #1, speed
	IF B$ = "radius" THEN INPUT #1, Radius
NEXT
CLOSE #1
 
Set1024x768 8
a$ = ""
a = 7
DIM stars(maxstars, a)
 
DO
 FOR n = 1 TO maxstars
	IF stars(n, 1) < 1 OR stars(n, 2) < 1 OR stars(n, 1) > 1024 OR stars(n, 2) > 768 THEN
		Future.FILLCIRCLE INT(stars(n, 1)), INT(stars(n, 2)), stars(n, 5), 0
		RANDOMIZE TIMER
		v = INT(RND(1) * 200) - 99: w = INT(RND(1) * 200) - 99
		IF v = 0 THEN v = 1: IF w = 0 THEN w = 1
		c = INT(RND(1) * 3) + 1
		SELECT CASE c
			CASE 1
				stars(n, 7) = 15
			CASE 2
				stars(n, 7) = 8
			CASE 3
				stars(n, 7) = 7
		END SELECT
		stars(n, 1) = v + 512: stars(n, 2) = w + 384
		stars(n, 5) = Radius: stars(n, 6) = INT(RND(1) * 10)
		l = SQR((v * v) + (w * w))
		SELECT CASE stars(n, 7)
			CASE 15
				speeda = speed
			CASE 8
				speeda = speed / 4
			CASE 7
				speeda = speed / 2
		END SELECT
		stars(n, 3) = v / l * speeda: stars(n, 4) = w / l * speeda
	END IF
	Future.FILLCIRCLE INT(stars(n, 1)), INT(stars(n, 2)), stars(n, 5), 0
	stars(n, 1) = stars(n, 1) + stars(n, 3)
	stars(n, 2) = stars(n, 2) + stars(n, 4)
	stars(n, 6) = stars(n, 6) + 1
	IF stars(n, 6) / 15 = INT(stars(n, 6) / 15) AND stars(n, 5) < 5 THEN stars(n, 5) = stars(n, 5) + 1
	Future.FILLCIRCLE INT(stars(n, 1)), INT(stars(n, 2)), stars(n, 5), stars(n, 7)
 NEXT
 a$ = INKEY$
LOOP UNTIL a$ <> ""
Palette.FadeOut
ReSetScreen
END

the StarScap.txt for the Qbasic:

[code]
maxstars
300
radius
2
speed
15
[\code]

This is a beautiful program in Qbasic, if anyone still has that on their system feel free to compile the QB code and run it via dosbox. You will need the future.bi QB library to run it. (like a class in Java)

I'll work more on this tomorrow.
Real quick question, setting the background color to black did not work, what am I doing wrong?!?!

setBackground(Color.black);

Originally Posted by Spidey1980

Real quick question, setting the background color to black did not work, what am I doing wrong?!?!

setBackground(Color.black);

Java is case sensitive.

Color (Java 2 Platform SE v1.4.2)

Colors can be either caps or lower, i.e BLACK or black (not BlAcK, ect.)

Anyways I found that setBackground(Color.black) does not set the background color. However this does:

g.setColor(Color.black);
g.fillRect(0,0,799,599);

It's getting closer, the first few stars move. You can see it now that the white stars are on a field of black:
(compile and run if you wish)

/* 
  StarScape Applet By Jon Crawford
  first Java tranlastion
 
*/
 
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class StarScape extends JApplet {
  public void paint(Graphics g){
    int maxStars = 200, starSpeed = 2, starRadius = 1, speedA;
    int v, w, c, l;
    int stars[][] = new int[maxStars+1][8];
    String i = "";
    g.setColor(Color.black);
    g.fillRect(0,0,799,599);
    do {
      for(int ctrl = 0; ctrl < maxStars; ctrl++) {
        //if star is out of range, and all of them are at start,
        //erase last star position, and give star a new random start
        if( stars[ctrl][1] <= 1 || stars[ctrl][2] <= 1 || stars[ctrl][1] >= 799 || stars[ctrl]
 
[2] >= 599) {
          g.setColor(Color.black);
          g.drawOval(stars[ctrl][1], stars[ctrl][2], starRadius, starRadius);
          Random rand = new Random();
          //start in small box in center
          v = rand.nextInt(200) - 99;
          w = rand.nextInt(200) - 99;
          if (v == 0) {
            v = 1;
          }
          if (w == 0) {
            w = 1;
          }
          //random color variable, specifies which of the three layers this star is in.
          //white = front, light grey = middle layer, dark grey = back layer
          c = rand.nextInt(3);
          stars[ctrl][7] = c;
          //adjust values to big box
          stars[ctrl][1] = v + 399;
          stars[ctrl][2] = w + 299;
          stars[ctrl][5] = starRadius;
          stars[ctrl][6] = rand.nextInt(10);
          //get angle
          l = (int)(Math.sqrt((v * v)+(w * w)));
          //adjust speed acording to color/layer
          switch (stars[ctrl][7]) {
            case 3:
              speedA = starSpeed;
              break;
            case 2:
              speedA = starSpeed / 4;
              break;
            case 1:
              speedA = starSpeed / 2;
              break;
            default:
              speedA = starSpeed;
          }//end case
          //calculate new star position from old star position
          stars[ctrl][3] = v / l * speedA;
          stars[ctrl][4] = w / l * speedA;
        }//end if
        //erase old star
        g.setColor(Color.black);
        g.drawOval(stars[ctrl][1], stars[ctrl][2], starRadius, starRadius);
        //set old position to new position
        stars[ctrl][1] = stars[ctrl][1] + stars[ctrl][3];
        stars[ctrl][2] = stars[ctrl][2] + stars[ctrl][4];
        stars[ctrl][6] = stars[ctrl][6] + 1;
        //stars get faster as they get closer every 15 steps
        if (stars[ctrl][6] / 15 == (int)(stars[ctrl][6] / 15) && stars[ctrl][5] < 5) {
          stars[ctrl][5] = stars[ctrl][5] + 1;
        }
        //use color/layer number to set the color
        switch (stars[ctrl][7]) {
          case 1:
            g.setColor(Color.white);
            break;
          case 2:
            g.setColor(Color.lightGray);
            break;
          case 3:
            g.setColor(Color.darkGray);
            break;
        }//end case
        //draw new Star
        g.drawOval(stars[ctrl][1], stars[ctrl][2], starRadius, starRadius);
      }//end for
      //check for key press
      //i = i + e.getKeyChar();
    }while (i == "");
  }//end paint
}//end Stascape

I probably have a few typos in my math, At least I have the working QB version to go from. I would think the math to be the same save for syntax across programming languages.

Originally Posted by Spidey1980

Colors can be either caps or lower, i.e BLACK or black (not BlAcK, ect.)

Well **** me. I always thought the constants in the Color class were all uppercase. Using setBackground should work. Did you get an error or did it just not work. If you got an error post it here. If it didn't work then perhaps you got things in the wrong order.

I read somewhere that it it sets the far backgroud color, it's a windows bug not Java. I could see the black background briefly when resizing the window.

Right now i'm working on drawing the stars correctly, and trying to figure out what went wrong in my vector math in translation. It's looks good, like a straight over copy with a little different syntax, but it just is not working.

Note, I start my star in a 200x200 box adjusted to -99 to 99 by -99 to 99 so I have 0,0 in the center. Vector math would not work otherwise. AFTER the angle is calculated then the coordintas are adjusted to the center of a 800x600 box that has 0,0 at top left to match the screen pixel coordinate system.

Also, can I use math.hypot(x, y) since it's output is the same as math.sqrt(x * x, y * y)? (source: Math (Java Platform SE 6)). I didn't do well past algebra 2. Yes, somebody else gave me the vector math (thank you Dr. Evil, Omni-bot creator), I was using (x-1,y-1) and (x-1,y+1) and (x+1,y-1) and (x+1,y+1) which allows for only 4 angles, vector math of course allows for thousands of angles within the 360 degree circle.

Do you think I should rewrite it so that it is more object orientated? right now it is more like an old school code from before object programming. Could that be the problem with my math?