final instance variable

/*
RULE:  we can declare instance variable as final but jvm wont provide any default values for instance variable, programmer have provide the values for final instance variables .
we can provide values in three ways
1. at the time of declaring the variable.
2. in constructor.
3.in instance block
*/

public class Final_Instance_Variable
{
final double d;
public static void main(String ar[])
{
System.out.println(x);     // compile time error
}
}

Way 1 : initialization value for final instance variable


public class Final_Instance_Variable
{
final double d=20.3;
public static void main(String ar[])
{
System.out.println(x);
}
}


Way 2 : initialization value for final instance variable


public class Final_Instance_Variable
{
final double d;
public Final_Instance_Variable()
{
d=20.3;
}
public static void main(String ar[])
{
System.out.println(x);
}
}



Way 3 : initialization value for final instance variable


public class Final_Instance_Variable
{
final double d;
{
d=20.3;
}
public static void main(String ar[])
{
System.out.println(x);
}
}