Why does java allow this
public class A {
private int i;
public A(int i){
}
}
but not this
public class A {
private final int i;
public A(int i){ // compile - time error
}
}
What is the difference push the item to the stack when it is final ? Why doesn't it understand that A(i) is different than final int i ?
Variable in constructor has nothing to do with final class member the compile time error you are getting is due to final variable is not just initilized .
Try this it will work
private final int i=0;
or
class A {
private final int i;
public A(int i){
this.i = i;
}
}
or
class A {
private final int i;
public A(int i) {
}//constructor over
{//initilizer block
i = 10;
}
}
compiler needs final member to be initialized while it initialize object.
final member field i isn't assigned a value before the instance is constructed.final member fields must be assigned before an instance's constructor finishes.
From Java Language Specification, 3rd Edition
8.3.1.2
finalFieldsA field can be declared
final(§4.12.4). Both class and instance variables (staticand non-staticfields) may be declaredfinal. It is a compile-time error if a blankfinal(§4.12.4) class variable is not definitely assigned (§16.8) by astaticinitializer (§8.7) of the class in which it is declared.A blank
finalinstance variable must be definitely assigned (§16.9) at the end of every constructor (§8.8) of the class in which it is declared; otherwise a compile-time error occurs.
It will allow the second snippet when you assign a value for i in the constructor:
public class A {
private final int i;
public A(int i){
this.i = i;
}
}
Note that this is how you create Immutable objects.
