Variables

Variables in Java work much like any programming language, here are the most common types:

Type	Description	Examples
bool	true or false	(true, false, 1, 0)
char	letter	('C', 'w', '!', '7')
double	decimal numbers	(2.82734105, -0.45, 1.1)
int	whole numbers	(1, 6782341, -84256689)
String	string of characters	("abcd", "Hi", "Hey There!")

Variables can be declared outside of a class but they can not have any values assigned to them outside of a class. Variable names can start with any valide letter, $, or _. It is worth noting that Java does support ++ and -- notation for adding and subtracting 1 respectively. String is written with a capital S and is unique in that we can also call upon the string class:

TODO Talk finish this example of string class.

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

One more thing to note about variables is if we want our variables to be unchangeable we can declare the variable with final. A final variable can not be changed and we will error out when we try to run our code if we do so.

Number manipulator

This is just a simple example of different forms of variable manipulation in Java. This a magic input/output trick. No matter what number we input into the inputNumber variable we will get the same number in outputNumber.

public class NumberManipulator {
    public static void main(String[] args) {
        // This is our original number so we are making it final
        final int inputNumber = 6;

        // This is the variable we are going to end with
        // Lets make this final as well to prove we aren't cheating
        final int outputNumber = 3;

        // Print out numbers
        System.out.println("Input number was: " + inputNumber);
        System.out.println("Output will be: " + outputNumber);

        // Set our mathNumber to inputNumber
        int mathNumber = inputNumber;

        // Now lets do some mathmatical manipulation on our outputNumber
        System.out.println("Now doing math on input number...");
        mathNumber *= inputNumber;
        mathNumber += inputNumber;
        mathNumber /= inputNumber;
        mathNumber += 17;
        mathNumber -= inputNumber;
        mathNumber /= 6;

        // Print out mathNumber
        System.out.println("Input number is now: " + mathNumber);

        // Check if they were equal
        boolean same = mathNumber == outputNumber;
        System.out.println("Input number is now equal to Output number: " + same);
    }
}

This is just a simple program to show off some of the things we can do with variable in Java. Here is a bigger list of some of the ways we can manipulate and use variables in Java:

Addition and subtraction: + and -
Multiplication and division: * and /
Modulo(remainder): %
Compound assignment operators: +=, -=, *=, /=, and %=
Greater than: >
Less than: <
Equal to: ==
Not equal to: !=
Greater than or equal to: >=
Less than or equal to: <=
Comparing Strings and other objects: .equals()
Concatenate Strings: "Hey " + name + "!"
Final variables: final

It is also important to note Java's order of operations:

parentheses
multiplication
division
modulo
addition
subtraction

Feel free to compile or run this progam, it is named: NumberManipulator.