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A variable is a placeholder for a value. Variables are also stored in the programming for a memory location that is filled with a value. Variables Variables are used for storing values. In Java, variables need to be defined with a data-type, to define its storage space requirements. The name of the variable must start with a letter, but can it may contain numbers in within the wordname. In processing, variable names are case-sensitive.

Variables also have a lifetime. The computer manages the storage of variables, and when the life span is over, the memory is released again (Garbage-Collector). The range (Scope) in which a variable is accessible or active is defined by brackets ({}) (see also classes and functions). Variables that are at the top level are called global variables as they are accessible all over the program. Variables declared within brackets are local variables. If a local variable has the same name as a global variable, the local variable overrides it within its scope.

// variablenvariable Declaration deklaration
int x1 = 15; // an integer i.e a whole number 
float valF = 0.323; // a floating point number i.e a numbers with a decimal point
boolean bFlag = false; // a true or false value i.e a single bit value
String message = "hallo 1"; // a collection of characters 
char character = 'g'; // a single character. Note the different quotation marks
 
String msg1 = new String("hallo 2");
 
println(x1);
println(valF);
println(bFlag);
println(message);
println(character);
println(msg1);

We can also makes make copies or combine variables. 

...

int length1 = 150;
int length2 = 200;
 
size(300,300); // define window size fenstergrosse
background(0); // define background colour
stroke(255,255,255); // define line colour
 
line(100,10,100,length1); // draw a line 
line(150,10,150,length2);
line(200,10,200,250);
 
fill(0,0,0); // fill colour
strokeWeight(5); // line thickness 
ellipse(100,length1,50,50); // draw an ellipse
ellipse(150,length2,50,50); // draw an ellipse
noFill(); // turn off fill
ellipse(200,250,50,50); // draw an ellipse

Primitive Data Types and Memory

Each kind of variable (it's data type) has an allocated amount of memory, which is enough to store a particular range of values. 

Operators 

An operator is a symbol that tells the computer to perform a particular math or logic operation. Some of the most common operators are:

+ Addition

/ Division

- Subtraction

* Multiplication 

These you already know but there are some very useful arithmetic operators you may not have seen in the following example:

int x1 = 10;

x1++; // increment value by one 
x1--; // decrement value by one
 
x1 += 2; // Add assign, this is the same as writing x1 = x1+2; 
x1 -= 2; // Subtract assign, this is the same as writing x1 = x1-2; 
x1 /= 2; // Divide assign (less common), this is the same as writing x1 = x1/2; 

Exercise 2:

Take your results from exercise 1 and modify your code to use variables. Create variable X and variable Y that can be used to position your graphic on the screen.