Welcome to Computer Programming



Just like in math, variables are used to represent other things - numbers (integers, doubles, floats), text (characters, strings) and things (ie dogs by a dog class)


  • Need to declare what type it is in order to use it. We also need to give the variable a name:
    • int weight; //so weight is the name and the type is int
    • Dog myDog;
    • Graphics g;
  • All variables have a scope (global [everywhere], local [some places]- where it can be accessed from: We will return to this soon.



  • We use camel case (with first lowercase) for variables that change; timeOfDay
  • name things appropriately; for example studentAverage is much better than sA or s
  • no spaces, cant start with number

There are 2 types of variables:

  • primitive - ints, doubles, boolean [there are others] - really basic stuff
  • non-primitive - OBJECTS - Strings, Square, Cars, Graphics
    • have methods and properties that can be done to them:
      • like g.drawLine(23,23,40,40) and stringName.length() or square1.makeVisible() or bunny.move(50,frog);

Primitive Types

Integers (whole numbers + and -)

- to declare a integer k and set its value as 50, we say

int k;


int k=50;

Now k has the value of 50;

Or if we wanted to add 30 to what k was:

k = k + 30;

If we wanted to add 1 to the value of i, we could


or shorter


and if you wanted to decrease by 1 you could i--;

We cant say:



Another example:

			int j=15/2;

j would then be: 7 (not 7.5).



-used to store real numbers, numbers with decimals; like money: 75.67 or someones average 92.37

-to use, same as using an integer:


double studentAverage;

double studentAverage=92.37;


Booleans are variables that represent simply true or false. They can be very useful when all you want is a variable to be on or off, (true or false). The values true or false are not in quotation marks.


boolean firstTime = true;

// the code below will be executed if firsttime is true
// note it is not necessary to say firstTime ==true, although it will not give an error
// if we wanted to do an if statment if it was false, we could say if (!firstTime)

if (firstTime)
    do this