Hot cup of Java sir?

int a;
float b;
boolean c;
String d;
a = 5;
b = 3.14;
boolean = true;
d = "Hi";

The above code will define four variables -

A integer
A real number
true or flase
text

Java is a typed language. This means you must say what data type a variable is before you are allowed to use it. This is known as defining the variable. If you do not define a variable you will get a error message. As shown in the example below

int a;
a= 5;
b = a + 1;

Example/src/example/MyFirstProgram.java:24: cannot find symbol
symbol : variable b
location: class example.MyFirstProgram
b = a +1;
1 error
BUILD FAILED (total time: 0 seconds)

Java is saying that you must define a variable before you are allowed to use it. This is a common rookie error. Just remember

If you do not define it you can not use it!

Basics