Variables and Primitive Types

How we store and save data in Java

What is a variable?

A variable is a container that is used for storing values.

Consider this analogy: a variable is like a vocabulary notecard. One side of the notecard is used for the word, and the other side is used for definition of that word. Here is an example of that in practice. int amount = 3;

This line of code is called a variable declaration, and consists of a left and right-hand side.

  • The left-hand side of a variable declaration has a data type (int) and a name (amount), in that order. This tells your computer that the variable amount has the data type int, which will never change.

  • The right-hand side is the value which the variable will store. In this case, the value will be 3.

Values can change, data types cannot.

Data Types

In the above example, variable amount is the type int. What does that mean?

As the name suggests, different data types specify what type of data can be assigned as the value to a variable. In Java, there are two kinds of data types: primitive and non-primitive.

Primitive Data Types

8 different primitive data types are available in Java. They consist of:

  1. boolean - true or false

  2. int - an integer value

  3. double - a decimal value

  4. char - a Unicode character

  5. long - like int but used for longer numbers

  6. float - like double with less precision

  7. byte - like int but in the range of -127 to 128

  8. short - like byte but with a range of -32,768 to 32,767

In most cases, only the first 4 of those types are used. The other 4 are mainly used when memory consumption on your computer is of utmost importance, which is not the objective of this course.

Why is Java not purely OOP?

As explained, Java has 8 primitive data types, as does the C programming language. However, this breaks the first law of pure OOP languages:

  1. Pre-defined types are objects

Those 8 primitive data types are primitives, meaning they are not objects. Furthermore, this means that you cannot directly call methods on them, but must instead use helper classes instead.

Quiz

Question
Answer
Question

How would you declare a variable age? Hint: use the int data type

Answer
int age = 15;