Variables

• In order to do useful things we need variables.
• What are variables?
  • way to store info
  • define by program
  • can be accessed
  • computer decides how to store them
  • contents can adjusted
  • Define
    • data type
    • name
    • value

Data types

• int - integer, whole number, no decimal

Declaration statement

• Define variable by data type, name, and option set of value

int myFirstNumber = 5;

• Initialization (to give value = 5) is optional
• In general, variables have to be initialized before being used

Expression

• Construct that evalutes to a single value
• More on this later

Back to code

• myFirstNumber is initialized to 5
• We don't care about memory location, Java does all the dirty work

Challenge

• Print out the variable myFirstNumber
• Done

public class Hello {

    public static void main(String [] args){
        System.out.println("Hello Harrison");

        int myFirstNumber = 5;

        System.out.println(myFirstNumber);
    }
}

• Mistake mentioned
  • System.out.println("myFirstNumber"); uses the string literal and not the variable
  • We told it to print the text and not to access the memory location and get the value from it

The expression can be more complex

• Lets add an expression for the sum of two numbers

public class Hello {

    public static void main(String [] args){
        System.out.println("Hello Harrison");

        int myFirstNumber = 10 + 5;

        System.out.println(myFirstNumber);
    }
}

• Java has looked at the expression and calculated the value to be 15
• Now something more complicated

public class Hello {

    public static void main(String [] args){
        System.out.println("Hello Harrison");

        int myFirstNumber = (10 + 5) + (2 * 10);

        System.out.println(myFirstNumber);
    }
}

Java Operators

• +,-,*,/ are common math operators that most are familiar with