why sometime we need to initialize integer variable ?

[Alvin chew]

hi, wondering why sometime we need to initialize the integer variable but sometime not ?

example :

 
int num1;
int num2;
 
num1 = rs.getInt("columname");  //num1 accepted 
num2 + = rs.getInt("columname"); // num2 having problem as shown error "num2 might not initialize"
 

can somebody pls explain why is it so i must initialize num2 ? thank you very much for your time

[William Brogden]

Class and instance variables are automatically given a starting value when the class is loaded or the instance is created. Variables declared inside a method are not.
Think about what the += operator does - it takes the existing value in a variable and adds to it. Therefore the compiler watches out for the possibility that num2 does not have a starting value assigned.
Automatically zeroing memory that a new object is going to occupy is part of the built-in security design of Java. In languages that don't do this, it is possible to grab a large hunk of memory that might have been used for data by a previous application and fish around in it for things like passwords.
Bill