A RevampingOf our skills so far

Our Tools so Far• Variable - a placeholder for a value

• Method - a set of code which accomplishes a task

• Class - a mold for an object

• Object Instance - a variable which holds an object value

• If statement - alters flow of control based on boolean condition(s)

Variables- Have a type, name, and value

int size = 5;

Ball myBall = new Ball(50, Color.RED, 6);

- Two kinds: Instance Variables and Local Variables

type name value

type namevalue

LOCAL VARIABLES

- declared and defined w/in a method

- can’t be accessed outside this method

public class Tire {

public Tire(){int radius = 40;

}

public int getRad(){return radius;

}

}

X

‘radius’ is local to the constructor method and therefore can’t be accessed in this method

INSTANCE VARIABLES

- declared outside any methods (still w/in class)

- can be accessed anywhere in the class

- use the private keyword

- should start with underscore

public class Tire {

private int _radius;

public Tire(){_radius = 40;

}

public int getRad(){return _radius;

}}

Methods-Block of code which can be called/executed

public double average (double num1, double num2){double sum = num1 + num2;

double average = sum / 2.0;

return average;}

-always public-can have as many parameters as you want (including none)-use return type of void if method won’t return anything

Modifier Return Type Method Name Parameters

void return type- Sometimes methods don’t need to return (output) anything- But every method needs to declare a return type

public void greeting (boolean isMale){if(isMale){

System.out.println(“Hello Sir”);}else{

System.out.println(“Hello Maam”);}

}

- note the lack of a return statement, void makes this fine!

Main Method

• This is where every java program starts• One main method per program• Looks like this:

public static void main (String [] args){//your java program starts here

}

Classes• The mold for our object instances• Made up of two things:

• Instance Variables – model properties of the class

• Methods – model abilities of the class

Our Classic Ball Examplepublic class Ball {

//instance variables go hereprivate int _size;private java.awt.Color _color;private int _bounciness;

public Ball(int size, java.awt.Color color, int bounciness){//this is the constructor method_size = size;_color = color;_bounciness = bounciness;}//here’s a methodpublic void setSize(int newSize){

_size = newSize;}

}

Object Instances

• Create one:

Ball myBall = new Ball(60, Color.BLUE, 11);

• Call methods on it:

myBall.setSize(30);

Now Something Random• Many times you want to be able to create some randomness• Java has a few solutions, here’s one:

Random rand = new Random();int randInt = rand.nextInt(5);

A Java library object

A method of the Random classrandInt will be

between 0 and 4

Call to Action

• Coding is inherently time-consuming

• You’ve been doing great work in lab

• But becoming a prolific coder will take more than 1.5hr/week

• You know enough to start embarking on your own projects outside of lab

• Dream big and start small

• Don’t be intimidated, you CAN do it! Stick with it!