In java, you can declare three different types of variables. They are instance, local, and class variables.
For instance variables:
# The primitive type (byte, short, int, long, float, double) variables are initialized to 0.
# Boolean initialized to false.
# char initialize to null.
For Class variables:
A class variable is a field within a class declared as static often referred to as a static variable or static field. It is also the same initialized as an instance variable.
For Local variables:
Local variables do not have a default value. They must be initialized before use. A local variable is a variable defined within a method, which includes any method parameters.
In a nutshell:
Data Type: Default Value:
int,short,byte / long 0 / 0L
float / double 0.0f / 0.0d
any reference type null