java – Variable might not have been initialized error

java – Variable might not have been initialized error

You declared them, but you didnt initialize them. Initializing them is setting them equal to a value:

int a;        // This is a declaration
a = 0;        // This is an initialization
int b = 1;    // This is a declaration and initialization

You get the error because you havent initialized the variables, but you increment them (e.g., a++) in the for loop.

Java primitives have default values but as one user commented below

Their default value is zero when declared as class members. Local variables dont have default values

Local variables do not get default values. Their initial values are undefined with out assigning values by some means. Before you can use local variables they must be initialized.

There is a big difference when you declare a variable at class level (as a member ie. as a field) and at method level.

If you declare a field at class level they get default values according to their type. If you declare a variable at method level or as a block (means anycode inside {}) do not get any values and remain undefined until somehow they get some starting values ie some values assigned to them.

java – Variable might not have been initialized error

If they were declared as fields of the class then they would be really initialized with 0.

Youre a bit confused because if you write:

class Clazz {
  int a;
  int b;

  Clazz () {
     super ();
     b = 0;
  }

  public void printA () {
     sout (a + b);
  }

  public static void main (String[] args) {
     new Clazz ().printA ();
  }
}

Then this code will print 0. Its because a special constructor will be called when you create new instance of Clazz. At first super () will be called, then field a will be initialized implicitly, and then line b = 0 will be executed.