Variables

In this lesson we’ll introduce you to variables.

What are Variables?

Variables are arguably the most important thing in programming any language. Variables consist of 3 main components:

1. The type
   This is what the variable stores, some examples are:
   • String - Stores text, such as “Hello”. String values are surrounded by double quotes.
   • int - stores integers (whole numbers), without decimals, such as 123 or -123.
   • double - stores floating point numbers, with decimals, like 19.99 or -3.14159265. Double values end with d. (for people with experience, we will not be using float in our code).
   • char - stores single characters, such as ‘a’ or ‘B’. Char values are surrounded by single quotes
   • boolean - stores values with two states: true or false
2. The name
   This is what the value is stored to, you use this name to reference its value
3. The value
   This is what the variable stores, it will be of the same type of the variable

The parts get arranged like so:

type name = value;

It’s important to note that the value is optional and the following is also a valid format:

type name;

If you use this, I would expect that you give it a value soon afterwards.

Some Examples

If I wanted to make a variable called message with a type of String and a value of Hello World I could do the following.

String message = "Hello World";
System.out.println(message);

The code above will print the value of the variable message which in this case is "Hello World".

double pi = 3.14159265d;
System.out.println(pi); // Prints 3.14159265

int number = 67;
System.out.println(number); // Prints 67

Assigning Later

The following is a example of how you can give a variable a value after declaring it.

int number;
number = 45;
System.out.println(number); // Prints 45

Notice how after declaring a variable, we don’t need to put the type next to it when assigning it a value.

Assigning Generally

We often find it useful to update a variable so here’s a example, it’s the exact same assigning syntax.

int number = 12;
number = 41;                // Changes number to 41
System.out.println(number); // Prints 41

number = 67;                // Changes number to 67
System.out.println(number); // Prints 67

Using Variables

Variables are useful in that they act as their value. Here are some examples of variables being used.

double x = 0.4d + 12.1d;    // After the =, we can put any expression that gives us a value, for example, math operations

double y = 2.4d + 0.1d;

double result = x + y;      // 12.5 + 2.5
System.out.println(result); // Prints 15

double x = 1;
x = x + 1;

System.out.println(x); // Prints 2

In our next lesson we’ll look at functions and how they are useful.