Variables
A variable stores some kind of information. The information stored can be retrieved at any time. You can store text, numbers and several other types of data using variables. For example:
int x = 2;
This stores the number 2 in a variable called x. int tells the
computer that the value you are assigning to the variable x is an integer (whole-number). The semicolon at the end is needed as creating (also known as instantiating) a variable is a statement.
Data Types
Every variable has a data type. A data type tells the computer what it’s storing in a specific variable. Without the data type, the computer has no idea if the value assigned to the variable is a number, text, or something else.
Let’s look back at the previous example:
int x = 2;
The computer needs the int at the beginning of the line to understand that the value
assigned to x in an integer. All variables are given data types in this way. You just put the data
type before the name of the variable.
Java includes many data types, but for now we’ll cover the 4 major ones:
StringsIntegersDoublesBooleans
Strings
Strings are used to store text. You can use a string to store your name, job, favorite color, etc. When you define a string, you need to make sure to put quotation marks around it. Notice how String is capitalized, while the other 3 major data types are not*.
String myName = "Bob Ross";
Integers
An integer is any whole-number. 0, 1, -2, 7, 456, and 8 are all integers, while 7.8, -12.5, and 32.6 are not. In Java integers can be positive or negative, they just have to be whole numbers. An integer is defined like this:
int secret = 42;
Doubles
Doubles are numbers, but they are more useful than integers. A double can be thought of as an integer that also supports decimal values. 0, 1, -2, and 7 are still acceptable values, but so are -3.1, 71.6 and 0.21. A double is defined like this:
double finalGrade = -0.32;
Booleans
A Boolean is a value that is either true or false. It can only be true or false, nothing else. A boolean are defined like this:
boolean isHungry = true;