# Inheritance

Inheritance

A class can be defined using another class as a foundation. In object-oriented programming terminology, one class can inherit fi elds and methods from another. An object that inherits from another is called a subclass, and the object it inherits from is called a superclass. A subclass extends the superclass.

```
SpinSpots spots;
SpinArm arm;

void setup() {
size(640, 360);
arm = new SpinArm(width/2, height/2, 0.01);
spots = new SpinSpots(width/2, height/2, -0.02, 90.0);
}

void draw() {
background(204);
arm.update();
arm.display();
spots.update();
spots.display();
}

class Spin {
float x, y, speed;
float angle = 0.0;
Spin(float xpos, float ypos, float s) {
x = xpos;
y = ypos;
speed = s;
}
void update() {
angle += speed;
}
}

class SpinArm extends Spin {
SpinArm(float x, float y, float s) {
super(x, y, s);
}
void display() {
strokeWeight(1);
stroke(0);
pushMatrix();
translate(x, y);
angle += speed;
rotate(angle);
line(0, 0, 165, 0);
popMatrix();
}
}

class SpinSpots extends Spin {
float dim;
SpinSpots(float x, float y, float s, float d) {
super(x, y, s);
dim = d;
}
void display() {
noStroke();
pushMatrix();
translate(x, y);
angle += speed;
rotate(angle);
ellipse(-dim/2, 0, dim, dim);
ellipse(dim/2, 0, dim, dim);
popMatrix();
}
}
```

## Functions Used

ellipse()

Draws an ellipse (oval) to the screen

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popMatrix()

Pops the current transformation matrix off the matrix stack

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rotate()

Rotates the amount specified by the angle parameter

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super

Keyword used to reference the superclass of a subclass

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size()

Defines the dimension of the display window width and height in units of pixels

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line()

Draws a line (a direct path between two points) to the screen

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stroke()

Sets the color used to draw lines and borders around shapes

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setup()

The setup() function is run once, when the program starts

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strokeWeight()

Sets the width of the stroke used for lines, points, and the border around shapes

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translate()

Specifies an amount to displace objects within the display window

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draw()

Called directly after setup(), the draw() function continuously executes the lines of code contained inside its block until the program is stopped or noLoop() is called

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background()

The background() function sets the color used for the background of the Processing window

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pushMatrix()

Pushes the current transformation matrix onto the matrix stack

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noStroke()

Disables drawing the stroke (outline)

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