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Thread: Setting constraints on a field

  1. #1
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    Default Setting constraints on a field

    i am coding a project that has "Shape" as the parent with various shapes (ie rectangle, triangle, etc.) as sub-classes using inheritance. i am supposed "Modify the constructor and set methods of the Shape class to verify the values of X and Y stay between zero and the MAX size. If X or Y are out of range, issue an error message on the console and set the value to zero." for some reason i cannot get it to work. when i run the program it will display the x-value even if it is out of range instead of zero. Here is the code for the parent class "Shape":

    public abstract class Shape {

    int x;
    int y;
    protected final static int X_MAX_SIZE=800;
    protected final static int Y_MAX_SIZE=600;

    //Constructor w/out parameters
    public Shape(){
    }
    //Constructor w/ parameters
    public void Shape(int x, int y){
    x=getX();
    if(x<0 || x>X_MAX_SIZE){
    System.out.println("ERROR!");
    this.x=0;
    } else this.x=x;
    y=getY();
    }
    public int getX(){
    return x;
    }
    public void setX(int x){
    if(x<0 || x>X_MAX_SIZE){
    System.out.println("ERROR!");
    this.x=0;
    } else this.x=x;
    }
    public int getY(){
    return y;
    }
    public void setY(int y){
    this.y=y;
    }

    public abstract double area();
    public abstract void display();
    public abstract void display(Graphics g);
    }


  2. #2
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    Default Re: Setting constraints on a field

    public void Shape(int x, int y){
    That is not a constructor!
    Improving the world one idiot at a time!

  3. #3
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    Default Re: Setting constraints on a field

    can you please clarify?

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    Default Re: Setting constraints on a field

    Why don't you find an example of a constructor (in a book or on a website) and compare it with what you have written.
    Improving the world one idiot at a time!

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    Default Re: Setting constraints on a field

    so i have a book for java and a professor that say that the following are constructors:

    public Shape(){
    }

    &

    public void Shape(int x, int y){
    }

    which i have both in my code.

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    Default Re: Setting constraints on a field

    Yes the first one is constructor of class Shape but not the second one.
    Constructor has no return type, neither void.

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    Default Re: Setting constraints on a field

    so i got rid of the void. not sure why i had it there in the first place cuz i dont have it it any of my other constructors within my project. but i still cant seem to get the program to verify that the variable "x" is in between 0 & 800. when i enter in a negative # (like -20) and run the program it still displays -20 instead of giving me the "ERROR!" message and assigning 0 to x.

  8. #8
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    Default Re: Setting constraints on a field

    x=getX();
    What's this line doing? Say, you are passing -20 to x in the parametrized(yours second) constructor and getX() will return you x's value that will be 0 as you didn't yet set.

  9. #9
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    Default Re: Setting constraints on a field

    quite honestly i have no idea why the "x=getX();" line is there, it was just my last effort in trying to get this to work. from my understanding, setX(); is supposed to set the new value for x. when i tried to set the new value for x using my constraints/verification

    if(x<0 || x>X_MAX_SIZE){
    System.out.println("ERROR!")
    this.x=0;
    }
    else this.x=x;

    it just sets the x value as -20

  10. #10
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    Default Re: Setting constraints on a field

    Yeah, so think logically, set before getting. Or simply remove x.getX() from the parametrized constructor.

  11. #11
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    Default Re: Setting constraints on a field

    so i took out the "getX();" line from the shape constructor:

    public Shape(int x, int y){
    this.x=x;
    this.y=y;
    }

    public int getX(){
    return x;
    }

    public void setX(int x){
    if(x<0){
    System.out.println("ERROR!");
    this.x=0;
    } else this.x=x;
    }

    I ran the program:
    "The Circle is located at the x-coordinate of -20 and the y-coordinate of 20 with a raiuds 40."

    It should show something like this:
    "The Circle is located at the x-coordinate of ERROR! 0 and the y-coordinate of 20 with a raiuds 40."

  12. #12
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    Default Re: Setting constraints on a field

    Can't you just debug it on your own now? Try to find out the behaviour of your program by placing PRINT statements after each statement and find it's behaviour.

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