Java - Default Values and Initialization

Question:

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

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

Using both IDE, the line System.out.println(a); will be an error pointing at the variable a that saysvariable 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? Does instance variable behaves different from local variables?

Answer:

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 default value .