a little confusion with my code .....

[dmjpro]

here is my code ....... plz look at carefully

class Test2
{
}

class Test1
{
void method(Test2 i)
{
System.out.println("Debasis: " + i);
}
}

class AnonymousTest
{
public static void main()
{
Test1 t = new Test1();
String str = "Debasis";
t.method(new Test2(){ public String toString(){return str;} });
}
}

now i get a compiler error ... the variable str needs to be declared as final

why this happens ... plz help....thanxxxxxx

[r035198x]

here is my code ....... plz look at carefully

class Test2
{
}

class Test1
{
void method(Test2 i)
{
System.out.println("Debasis: " + i);
}
}

class AnonymousTest
{
public static void main()
{
Test1 t = new Test1();
String str = "Debasis";
t.method(new Test2(){ public String toString(){return str;} });
}
}

now i get a compiler error ... the variable str needs to be declared as final

why this happens ... plz help....thanxxxxxx

1.) dj you forgot the code tags again!
2.)You are accessing a local variable from an inner class therefore it must be declared final

[dmjpro]

again sorrry .....thanx for ur replyyyy

i know i trying to access the local varibale ... so it needs to be declared as final

but i want to know if the java compiler allows to do so then what would happen.....
i just want to know what is the logic behind it ....

plz help me .... thanxxxxx

[r035198x]

again sorrry .....thanx for ur replyyyy

i know i trying to access the local varibale ... so it needs to be declared as final

but i want to know if the java compiler allows to do so then what would happen.....
i just want to know what is the logic behind it ....

plz help me .... thanxxxxx

It's a memory allocation issue dj. When memory for the inner class object is reserved, everything about it needs to be known at that moment so that the best fit slot is selected for it. That's why the variable allowed for it must be final.

[dmjpro]

it is not still clear to me ..... if u can't explain me in one thread ... plz send me a good link which can describe in details...

plz help ..... thanx

[r035198x]

it is not still clear to me ..... if u can't explain me in one thread ... plz send me a good link which can describe in details...

plz help ..... thanx

Try this but you may need to read the JVM specification to fully understand this.

[dmjpro]

thanx a lot ... have a good day

[dmjpro]

hello frndsss ..... i got a good exlaination on it .... if can plz check it out



written by hiwa from java world


See: http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.1.3
An inner class, however it is declared and defined in a particular method, makes a separate object outside the method so the object can't access method local variables, which are allocated on the mthod's stack frame, directly. Thereof that enforces Java to pass a copy of local variable to the inner class object.

// str is a copy of local variable str!!!
t.method(new Test2(){ public String toString(){return str;} });

If the method happens to modify the value of the local var, the new value doesn't reflect to the copy in the inner class object -- that should invite a terrible disaster. In order to prevent it, local var referenced in an inner class must be final.