Lesson 3

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Lesson 3

Data Types

Java is a statically typed language. A language is statically typed, if the data type of a variable is known at compile time. This means that you must specify the type of the variable (Declare the variable) before you can use it.

A data type defines the type of values that a variable can have assigned to it. For example if a variable has int data type, it can only take integer values. In java we have two categories of data types: 1) Primitive data types 2) Non-primitive data types – Strings and arrays are non-primitive data types.

Primitive data types

In Java, we have eight primitive data types: boolean, char, byte, short, int, long, float and double.

byte, short, int and long data types are used for storing whole numbers.

float and double are used for fractional numbers.

char is used for storing characters(letters).

boolean data type is used for variables that holds either true or false.

Non-primitive data types

Two data types in Java are not considered primitive. String and arrays. You have already seen how to create a String, but you may be wondering why it is not a primitive. String variables have methods that you can use as well as properties! We will discuss methods in a later lesson. But this is the reason that String is not considered a primitive.

Arrays are used to describe a list of variables. Example:

int arr[]={2,11,45,9};

this array is a list of int and it has four values in it. Note that you cannot grow or shrink an array. This makes them a bit inflexible. They definitely have their place in our toolbox, but we have some better options that provide us more functionality. We will talk about arrays and lists in a later lesson.

Exercise

In Lesson 2 we added variables to your Superhero. The data type we picked for the variables was a String. Look at those variables and decide if they should stay as String or if a different data type would be appropriate. Change or add two variables in your Superhero and use a data type that is NOT a String. In the example below, we have added an "age" variable of type int. Note that primitive values do NOT have any quotes around the value.

Code

class Main {
  public static void main(String[] args) {
    Superhero me = new Superhero();
    me.name = "Groot";
    me.age = 10;
    System.out.println(me.name);
    System.out.println(me.age);
  }
}

class Superhero
{
  String name;
  int age;
}