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Thread: Creating Objects: A question about the Java Tutorials example program

  1. #1
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    Default Creating Objects: A question about the Java Tutorials example program

    Hello All,

    So I've been trying to learn Java to write a browser based text adventure and to do this I've been going through the standard java tutorials found here:
    Objects (The Java™ Tutorials > Learning the Java Language > Classes and Objects)

    I put together a program from the three classes they describe on that page in the netbeans compiler as follows:

    /*
     * To change this template, choose Tools | Templates
     * and open the template in the editor.
     */
    package experiment.ground;
    /**
     *
     * @author Geoffrey
     */
     
     
    public class ExperimentGround {
     
     
     
        public static void main(String[] args) {
     
            // Declare and create a point object
            // and two rectangle objects.
            Point originOne = new Point(23, 94);
            Rectangle rectOne = new 
                Rectangle(originOne, 100, 200);
            Rectangle rectTwo =
                new Rectangle(50, 100);
     
            // display rectOne's width,
            // height, and area
            System.out.println("Width of rectOne: "
                               + rectOne.width);
            System.out.println("Height of rectOne: "
                               + rectOne.height);
            System.out.println("Area of rectOne: "
                               + rectOne.getArea());
     
            // set rectTwo's position
            rectTwo.origin = originOne;
     
            // display rectTwo's position
            System.out.println("X Position of rectTwo: "
                               + rectTwo.origin.x);
            System.out.println("Y Position of rectTwo: "
                               + rectTwo.origin.y);
     
            // move rectTwo and display 
            // its new position
            rectTwo.move(40, 72);
            System.out.println("X Position of rectTwo: "
                               + rectTwo.origin.x);
            System.out.println("Y Position of rectTwo: "
                               + rectTwo.origin.y);
        }
    }
     
    public class Point {
        public int x = 0;
        public int y = 0;
        // a constructor!
        public Point(int a, int b) {
        x = a;
        y = b;
        }
    }
     
    public class Rectangle {
        public int width = 0;
        public int height = 0;
        public Point origin;
     
        // four constructors
        public Rectangle() {
        origin = new Point(0, 0);
        }
        public Rectangle(Point p) {
        origin = p;
        }
        public Rectangle(int w, int h) {
        origin = new Point(0, 0);
        width = w;
        height = h;
        }
        public Rectangle(Point p, int w, int h) {
        origin = p;
        width = w;
        height = h;
        }
     
        // a method for moving the rectangle
        public void move(int x, int y) {
        origin.x = x;
        origin.y = y;
        }
     
        // a method for computing the area of the rectangle
        public int getArea() {
        return width * height;
        }
    }
    }

    This program does not accept the declaration of the last two classes and says that they have to be declared in a files (I'm not sure what that means).

    I'm working without any guidance here aside from the tutorials. I would really appreciate it if someone would tell me what I'm doing wrong.

    Thank you in advance!


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    Default Re: Creating Objects: A question about the Java Tutorials example program

    I'm guessing the classes need to be separate files in the same package. I'm going to try that out.

  3. #3
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    Default Re: Creating Objects: A question about the Java Tutorials example program

    First off, there's no such thing as a "netbeans compiler". Netbeans is an IDE, the compiler is part of the JDK.

    But the problem is that you're trying to declare more than one top-level public class inside a file. Think about it this way: if you make them public, how do other classes in different files know where to find them? They don't, unless you put them in their own file. You could get rid of the public declaration, but you're probably better off putting them in their own files.
    Useful links: How to Ask Questions the Smart Way | Use Code Tags | Java Tutorials
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