01 - Variables & Data Types

Variables are containers that store data in your program. Think of them as labeled boxes where you can put different types of information.

What is a Variable?

A variable has three key components:

1. Type: What kind of data it holds (e.g., integer, string, boolean)
2. Name: The label you use to refer to the variable
3. Value: The data it contains

Declaring/Creating Variables

In Java, you must declare a variable before using it, like you'd need a box before putting something in it. The syntax is:

int age;
age = 18;

int age = 18; // Declaration and assignment in one line

Primitive Data Types

You might wonder what "int" means. It's a primitive data type in Java. Java has 8 primitive data types. Here are the most important ones for modding:

Type Conversion

Sometimes you might not want a variable to stay the same type. You can convert between types:

Automatic

int num = 10;
double decimalNum = (double) num; // 10.0 - works automatically

Manual (Casting)

double decimalNum = 9.78;
int num = (int) decimalNum; // 9 - decimals are dropped

Constants

If you want a variable that shouldn't change, use the final keyword:

final double PI = 3.14159;

Convention: Constants use ALL_CAPS_WITH_UNDERSCORES.

Practice

It's best to practice what you just learnt - don't look above now and try to do this yourself. If you get stuck, look back up!

1. Declare an integer variable named lives and set it to 3.
2. Declare a double variable named gravity and set it to 9.81.
3. Declare a boolean variable named isGameOver and set it to false.
4. Convert the lives variable to a double and store it in a new variable named livesAsDouble.
5. Declare a constant named MAX_LEVEL and set it to 100.

Great! You've learned about variables and data types in Java. Now we're going to learn about operators and expressions in the next lesson.