Embed Size (px)
Citation preview
Introduction to Objects
What is a constructor?
Use type to create a variable
Use class to create an object
int x;
Circle mycircle = new Circle();
Let’s start simple
A circle
What are some of the attributes of a circle?
• Radius (most obvious)
• Color
• Border
• Position
Let’s start with a simple Circle class
• Just a radius– No borders or colors
• A means of asking it for it’s area.
• This will serve as the basis (a type or class) for creating lots of circles
Circle()
class Circle {
double radius;
Circle(double r) { radius = r; }
double Area() { double this area = radius*radius*Math.PI; }
}
Circle()
class Circle {
double radius;
Circle(double r) { radius = r; }
double Area() { double this area = radius*radius*Math.PI; }
}
Heading for the class
Circle()
class Circle {
double radius;
Circle(double r) { radius = r; }
double Area() { double this area = radius*radius*Math.PI; }
}
A property ofeach circle
Circle()
class Circle {
double radius;
Circle(double r) { radius = r; }
double Area() { double this area = radius*radius*Math.PI; }
}
A method named Areathat will calculate thearea of that specific circle
Circle()
class Circle {
double radius;
Circle(double r) { radius = r; }
double Area() { double this area = radius*radius*Math.PI; }
}
A constructorUsed to initialize the circleLet’s see how in the next slide
-Name same as the class-No type
Creating circles
Circle circle1 = new Circle(10);
Radius:10
circle1
Creating circles
Circle circle1 = new Circle(10);
radius:10
circle1
Circle circle2 = new Circle(15);
radius:15
circle2
What’s the difference?
• Circle circle1 = new Circle(10);
• Circle circle1; Creates a REFERENCELike having a telephone number for a friend.. a means to find them. Butthis one is a contact without a number.
Creation requires a new
new uses the constructor
Circle()a default constructor
class Circle {
double radius;
Circle() { radius = 1.0; }
Circle(double r) { radius = r; } double Area() { double this area = radius*radius*Math.PI; }
}
Another constructorThis constructor chooses a radius (1) for us.
Creating circles
Circle circle1 = new Circle();
radius:1
circle1
Circle circle2 = new Circle(15);
radius:15
circle2
default constructor
Circle() : more constructorsclass Circle { double radius,x,y;
Circle() { radius = 1.0; x=0.0; y=0.0; }
Circle(double r) { radius = r;
x=0.0; y=0.0; } Circle(double r,double xpos, double ypos ) { radius = r;
x=xpos; y=ypos; } }
Circle() : more constructorsclass Circle { double radius,x,y;
Circle() { radius = 1.0; x=0.0; y=0.0; }
Circle(double r) { radius = r;
x=0.0; y=0.0; } Circle(double r,double xpos, double ypos ) { radius = r;
x=xpos; y=ypos; } }
Circle c1 = new Circle();
Circle() : more constructorsclass Circle { double radius,x,y;
Circle() { radius = 1.0; x=0.0; y=0.0; }
Circle(double r) { radius = r;
x=0.0; y=0.0; } Circle(double r,double xpos, double ypos ) { radius = r;
x=xpos; y=ypos; } }
Circle c2 = new Circle(10.0);
Circle() : more constructorsclass Circle { double radius,x,y;
Circle() { radius = 1.0; x=0.0; y=0.0; }
Circle(double r) { radius = r;
x=0.0; y=0.0; } Circle(double r,double xpos, double ypos ) { radius = r;
x=xpos; y=ypos; } }
Circle c3 = new Circle(10.0,1.0,2.0);
As many constructors as you want!
