Variables

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)

• Values can change or be permanent (if permanent they are called final variables; ie INCHESINFOOT = 12)
• 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
  • char c;
  • float average;

• All variables have a scope (global [everywhere], local [some places]- where it can be accessed from: We will return to this soon.

   

Remember

• 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

There are 2 types of variables:

• primitive - ints, doubles, char, boolean [there are others]
• non-primitive - OBJECTS - Strings, Square, Cars, Graphics
  • have methods and properties that can be done to them:
    • like 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;
k=50;

or

 
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

 
i=i+1;

or more concisely

 
i++;

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

If we said

 

			k=60.4;

We'll we declared k as an int, so k actually would lose the .4, and just be 60 - this is bad news.

Another example:

			int j=15/2;

j would then be: 7 (not 7.5).

Doubles

-used to store real numbers, numbers with decimals; $75.67 or someones average 92.37

-to use, same as using an integer:

  
double studentAverage;
studentAverage=92.37;
            

  

double studentAverage=92.37;

char

Chars are used to represent one letter only. Case matters, as always in java. You put ' ' around the character to set it.

for example:

char myLetter = 'a';

Boolean

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
}