Lab Quiz 2

Pledged lab quiz

The only "good programming practice" that is required for this lab is to include your name and e-mail ID in the header comments. You are welcome to include more, but make sure you get the programs working first, as the quiz is timed.

The activities of this week are not to be discussed outside of lab. The quiz is open textbook but nothing else. You are to submit one program, Star.jara, which contains the Star class.  A template file is being provided.  There are to be 9 methods in Star.java, 4 of which we provide.  The Star class represents a astronomical star, to be used in a computer program.

Instance variables

The sample Star.java file contains four double instance variables to represent the brightness and location of the star.  The brightness of the star will be a positive number (this is not the same as astronomical magnitude).  The other three instance variables together represent the  (x, y, z) location of the star.  Our template file Star.java provides the following definitions for them.

private double brightness;
private double xLocation;
private double yLocation;
private double zLocation;
 

Methods

You are to implement five methods in the Star class.

• public Star()
  The default constructor, it should set the brightness to 1, and the location to (0,0,0)
   
• public Star (double b, double x, double y, double z)
  The specific constructor, it should set the brightness to b, and the location to (x, y, z)
   
• public void setLocation (int which, double toWhat)
  One of the two mutators (we implement the other mutator).  Parameter which specifies which location part of the ordered triple to set, and parameter toWhat specifics the value to which it is set.  If parameter which is 1, then the x location of the Star is set to the value of toWhat.  A which value of 2 sets the y location, and a which value of 3 sets the z location.  If which is less than 1, or greater than 3, then no modification should be made to the Star's location  (i.e., the request is ignored).  For example, if star is a Star object, then star.setLocation(1,2) will set the x value of the location to 2.
   
• public double getLocation (int which)
  One of the two accessors (we implement the other accessor).  This returns one of the location parts: if which is 1, it returns the x location,  if which is 2, it returns the y location, and if  if which is 3, it returns the z location.  If which is less than 1 or greater than 3, then this should return 0.
   
• public double distance()
  This method will return the distance of the star from the origin (0,0,0).  The distance of location (x,y,z) from the origin is the square root of (x*x + y*y + z*z). In case you do not recall, you can get the square root of an expression e in Java with

Math.pow(e, 0.5).

The template Star.java file provides the following additional three methods -- DO NOT CHANGE THEM.

• public void setBrightness (double b)
  One of the two mutators, it sets the brightness to the parameter b
  
  public void setBrightness (double b) {
      brightness = b;
  }
   
• public double getBrightness ()
  One of the two accessors, it returns the brightness of the Star
  
  public double getBrightness () {
      return brightness;
  }
   
• public String toString()
  This method must be copied EXACTLY as shown below.
  
  public String toString() {
          return "Star (" + brightness + ", @ ("
                          + xLocation + ", "
                          + yLocation + ", "
                          + zLocation + "))";
  }
   

If you want to test your program you are welcomed to copy and paste into it your class. Because we will have our own testing program, it will not affect your grade whether it is included or not.

public static void main (String[] args) {

    Star s1 = new Star();
    System.out.println (s1);
    Star s2 = new Star (3, 1, 2, 3);
    System.out.println (s2);

    s1.setBrightness (5);
    s1.setLocation (0, 10);    // This should do nothing!
    s1.setLocation (1, 11);
    s1.setLocation (2, 12);
    s1.setLocation (3, 13);
    s1.setLocation (4, 14);    // This should do nothing!
    System.out.println (s1);

    double x = s2.getLocation(1);
    double y = s2.getLocation(2);
    double z = s2.getLocation(3);
    System.out.println ("s2's location is (" + x + ", " + y + ", " + z + ")");

    System.out.println ( s1.distance() );
    System.out.println ( s2.distance() );
}

Sample Output

The main() method above will produce the following output.

Star (1.0, @ (0.0, 0.0, 0.0))
Star (3.0, @ (1.0, 2.0, 3.0))
Star (5.0, @ (11.0, 12.0, 13.0))
s2's location is (1.0, 2.0, 3.0)
20.83266665599966
3.7416573867739413

Grading

Make sure each of your methods are named EXACTLY as specified.  Also, DO NOT CHANGE the other methods as they are used by the grading system.  If you do not follow these directions, the grading system will give you a zero for pretty much all of the lab quiz.

Advice

• Remember neither the lab assistants nor other students may help you design, write, or debug the programs. If you are having a problem getting JCreator to work right (which does not mean a compilation error), or an error with the submissions, then you may ask a TA.
   
• To maximize your points, make sure your programs compile successfully.
   
• If towards the end things are not going as well as you would want (i.e., the program does not compile), it might be best to try commenting out errant statements (i.e., put a // in front of them)

Submission

When you are finished, submit your Star.java file.