random not working in .class method

Just wondering, why does Math.random() (or any random technique) not work in a constructor or setMethod? It just outputs Null. However Math.sqrt(), ect. does work inside the method.

Once I moved the Math.random() to my main class, sending the result to the setMethod, everything started to work like magic.

Note: both the class and the main have "import java.math.*;"

Post the code as an SSCCE that demonstrates the error...the Math class is in the java.lang package which is a default import - there shouldn't be a need to import the java.math package.

Math (Java 2 Platform SE v1.4.2)

Quote:

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It just outputs Null

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Math.random()'s return type is double. It cannot return null.

Always, always post code that demonstrates the issue, particularly if the problem is impossible.

when I had the random in the setMethod, I had a println right after it.

pseudo - code:

Code :

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public class Test()
{
public void test()
{
numberX = random() * 100
numberY = random() * 100
print ("\t" + numberX + "\t" + numberY) 
}
}

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outputs

Code :

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null       null

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however:

Code :

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public main()
{
numberX = random() * 100
numberY = random() * 100
object[index].setData (numberX, numberY)
myX = object[index].getX()
myY = object[index].getY()
print ("\t" + myX + "\t" + myY)
}

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outputs:

Code :

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47       82

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Please don't post Java that won't compile. My pseudocode also occasionally prints null. Or does it? Who can tell?

Only object references can have the value of null. If numberX is an int or double, it would have a printable value.

Your posted code is useless.

You were asked for an SSCCE in the first response. Save us all a lot of time and just throw one together.

lol i'm so far past that anyways. Moving the randoms to the main and calling a set works well. And sorry, it output "NaN" since I'm working with doubles, not Null.

Here it is then.....
look for this line in folowing code:
{//resetStar method<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< <<<<<<<<<<<<<<<<<<<<<<here, look at next four lines

Star.java

Code java:

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// star.java
// by Jon Crawford
package Star;
 
import java.util.*;
import java.math.*;
 
public class Star {
  int myX;
  int myY;
  int myLayer;
  private final int starSpeed = 1;
  private final int starRadius = 1;
  private final int starSteps = 0;
  private final float[] invalidValues = new float[]{ -399f, -299f, 399f, 299f, 0f, 0f};
  private String isValid = "false";
  private double starAngle;
  private double starField[] = new double[9];
 
  public void Star(double myX, double myY, double myLayer)
  {
    starAngle = (Math.sqrt((myX * myX)+(myY * myY)));//calculate the hypotenuse
    starField[0] = myX;//set data to star's arrary
    starField[1] = myY;//this is for current position
    starField[2] = myX / starAngle * starSpeed;//these set the next position
    starField[3] = myY / starAngle * starSpeed;//this is reltive current position
    starField[4] = myLayer;//back, mid, or foreground layer
    starField[5] = starRadius;//star starting size
    starField[6] = starSpeed * myLayer;//the starting speed
    starField[7] = starSteps;//star has taken 0 steps, every 5 steps star grows and speeds up
    starField[8] = starAngle;//store the hypotenuse
  }//end constructor
 
  public void moveStar() 
  {//mutator method
    System.out.println("") ;    
    starField[0] = starField[0] + starField[2];//next position becomes the curent position 
    starField[1] = starField[1] + starField[3];       
    starField[2] = starField[0] / starField[8] * starField[6];//new next position
    starField[3] = starField[1] / starField[8] * starField[6];
    starField[7] = starField[7] + 1;//increment steps
    if (starField[7] / 5 == (int)(starField[7] / 5) && starField[5] < 20)
    {//if star has taken 5 steps
      starField[5] = starField[5] + 1;//increment size
      starField[6] = starField[6] + 1;//increment speed
    }//end if      
  }//end moveStar
 
 /* public void resetStar(double myX, double myY, double myLayer) */
/*  ^^sending the values from the main works well, commented out for comparison ^^*/
  public void resetStar()   /* if random in here, no need to send in variables from main */
  {//resetStar method<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<here, look at next four lines
    myY = Math.random() * 200 - 99;
    myX = Math.random() * 200 - 99;
    myLayer = Math.random() * 3;
    System.out.println("\t" + myX + "\t" myY + "\t" + myLayer);
/* output of this is outside of highlight tag */
    starAngle = (Math.sqrt((myX * myX)+(myY * myY)));//calculate new hypotenuse
    starField[0] = myX;//set data to star's array
    starField[1] = myY;//same as default constructor
    starField[2] = myX / starAngle * starSpeed;
    starField[3] = myY / starAngle * starSpeed;
    starField[4] = myLayer;
    starField[5] = starRadius;
    starField[6] = starSpeed * myLayer;
    starField[7] = starSteps;
    starField[8] = starAngle;
  }//end resetStar
 
  public void starValid()
  {//isValid method
    if(starField[0] > invalidValues[0] && starField[1] > invalidValues[1] && starField[0] < invalidValues[2] && starField[1] < invalidValues[3])
    {//in bounds?
      isValid = "true";
    }else
    {//out of bounds
      isValid = "false";
    }//end if
  }//end is valid
 
  public int getStarX() 
  {//get method
    return (int)(Math.round(starField[0]));
  }//end getStarX
 
  public int getStarY() 
  {//get method
    return (int)(Math.round(starField[1]));
  }//end getStarY
 
  public int getStarRadius() 
  {//get method
    return (int)(Math.round(starField[5]));
  }//end getStarRadius
 
  public int getStarLayer() 
  {//get method
    return (int)(Math.round(starField[4]));
  }//end getStarLayer
  public String getValid()
  {//get method
    return isValid;
  }//end isValid
 
}//end class star

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Console output using appletviewer:
NaN NaN NaN
NaN NaN NaN

this repeats indefinately.

of course to see this output properly the StarScape.java needs to be edited to remove randoms and just call resetStar without passing any variables.
these four lines should be added to the constructor as well.


properly working code posted in http://www.javaprogrammingforums.com...-day-12-a.html

That is not an SSCCE - see my signature. The code you posted wouldn't even compile:

Code :

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myY = Math.random() * 200 - 99;

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should yield a compile time error type mismatch - myY is an int and the right side a double

so I wrote up small example.java and a testRand.java subclass. Guess what? It works perfect! so something in my big starscape program messed it up, not the random function itself.

Since I crated this thread could a moderator delete this please?

Quote:

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Originally Posted by Spidey1980

random does not not work in side a user made subclass method

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I don't understand. Don't blame the API and the J2SE - it has worked for thousands if not millions of applications. It has been put through the ropes, and I guarantee it works if used appropriately. Almost always the problem is a result of misuse, and until you post an SSCCE that demonstrates your issue its hard to determine where the problem lies.

Quote:

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Originally Posted by Spidey1980

never mind I'm not going to de-evolve my code just for a point.

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Nobody wants to steal your code.

Quote:

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random does not not work in side a user made subclass method

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Incorrect! Random works perfectly well regardless of where you place it in your code. If it doesn't produce your expected results then either your expectations or your code is wrong.

Could a problem be that this line is NOT a constructor:

Code :

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 public void Star(double myX, double myY, double myLayer)

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