How are variables defined in Java?

In Java, variables can be defined using the following syntax:

Variable name of data type;

For example, declaring a variable of type integer:
int num;

Declare a variable of type String:
String name;

Declare a variable of boolean type:
boolean isTrue;

It is also possible to assign initial values to variables when defining them, for example:
int age = 20;
String city = “Beijing”;
boolean isMale = true;

It is important to note that variable names must follow certain naming conventions, such as not starting with a number, not containing spaces or special characters, etc. Additionally, Java is a strongly typed language, so when defining variables, you must specify the data type of the variable, and the data type of the variable cannot be changed.