Default values and initialization in Java

Question

Based on my reference, primitive types have default values and Objects are null. I tested a piece of code.

public class Main {     public static void main(String[] args) {         int a;         System.out.println(a);     } } 

The line System.out.println(a); will be an error pointing at the variable a that says variable a might not have been initialized whereas in the given reference, integer will have 0 as a default value. However, with the given code below, it will actually print 0.

public class Main {     static int a;     public static void main(String[] args) {         System.out.println(a);     } } 

What could possibly go wrong with the first code? Do class variables behave different from local variables?

Answer 1

In the first code sample, a is a main method local variable. Method local variables need to be initialized before using them.

In the second code sample, a is class member variable, hence it will be initialized to the default value.