Circle class

public class Circle { private static int instanceCnt = 0; private double radius;

public static int getInstanceCnt() { return Circle.instanceCnt; }

private static void setInstanceCnt(int insCnt) { Circle.instanceCnt = insCnt; }

public Circle() { }

public Circle(double newRadius) { Circle.setInstanceCnt(Circle.getInstanceCnt() + 1); this.setRadius(newRadius); }

public Circle(Circle guest) { }

public double getRadius() { return this.radius; }

private void setRadius(double radius) { if (radius >= 0) this.radius = radius; else this.radius = 0; }

public void resize(double newRadius) { this.setRadius(newRadius); }

public Circle clone() { return new Circle(this.getRadius()); }

public boolean equals(Circle guest) { return guest.getRadius() == this.getRadius(); } public void print() { System.out.print("The circle\'s radius is " + this.getRadius()); } }

Main topics:

Writing Classes Declaring / Using Instance Variables

Writing Instance Methods

Accessors and Mutators

public vs private

Constructors

Member method overloading

static vs non-static

final vs non-final

Exercise

This week you will get more practicing writing a complete class, starting from where you left off last week, which includes class and instance constants. Again careful attention to the public, private and static specifiers will be made.

Getting Started

To start this exercise, you should:

1. Open eclipse and start a new Java project named Lab04

2. Add a Class (named Circle) to this project, and copy the contents of the Circle file provided into it.

3. Add a Class (named CircleDriver) to this project, the contents of which you will be writing from scratch.

Requirements

Circle.java

A simple class which models a circle by its one defining characteristic, which is its radius. This class is moderately complete and must be modified as such:

1. Both the default and copy constructors simply call the specifying constructor, with the appropriate argument

2. Include a class constant for PI Whose value is the best approximation of PI you can store ( public or private? static or not? final or not? )

3. Include an instance constant for units Whose default value is cm ( public or private? static or not? final or not? ) 4. The print() method is modified to include the units the radius is given in

5. Include an overloaded 0-arity mutator for the radius value that sets the radius value to 0 ( where is the one and only place it make sense to call this? )

6. Include an area method that returns the area of the circle in units squared

CircleDriver.java

A simple driver class to test your additions to the Circle class. This class you are writing from scratch, but must include sufficient code to test all of the new features listed above.

________________________________________________________________

This is what I have done so far for the Circle class and I have also added comments

public class Circle

{

private static int instanceCnt = 0;

private static final double pi = 3.14;

private double radius;

private final String unit;

public static int getInstanceCnt()

{

return Circle.instanceCnt;

}

private static void setInstanceCnt(int insCnt)

{

Circle.instanceCnt = insCnt;

}

//default

public Circle()

{

this(0.0,"cm");

}

//specifying

public Circle(double newRadius, String units)

{

Circle.setInstanceCnt(Circle.getInstanceCnt() + 1);

this.setRadius(newRadius);

this.unit = units;

}

//copy

public Circle(Circle guest)

{

this(guest.getRadius(),guest.unit);

}

public double getRadius()

{

return this.radius;

}

public double getArea()

{

return (pi*radius*radius);

}

public String getUnit()

{

return this.unit;

}

/* public void unit (String unit)

* {

* this.unit.equals("cm");

* } */

private void setRadius(double radius)

{

if (radius >= 0)

this.radius = radius;

else

this.radius = 0;//create new method that sets radius to zero and call it here

}

public void resize(double newRadius)

{

this.setRadius(newRadius);

}

public Circle clone()

{

return new Circle(this.getRadius(),this.getUnit());

}

public boolean equals(Circle guest)

{

return guest.getRadius() == this.getRadius();//compare units also

}

public void print()

{

System.out.print("The circle\'s radius is " +

this.getRadius());

}

}