please answer my query?

[payal sharma]

I am unable to understand this?

import java.util.*; 
    public class AllFinals 
    { 
         
                final Vector v; 
                 v=new Vector();
        
        public AllFinals() 
        { 
        } 
        public void someMethod() 
        { 
                System.out.println(v.isEmpty()); 
        } 
   } 

here why I am getting compile time error as AllFinals.java:7: Identifier expected.
v=new Vector();
Although I am changing the refrence of the final object not the object itself.
I can change its reference in contructor if I put v=new Vector() in constructor.
but here

import java.util.*; 
public class AllFinals 
    { 
        final Vector v; 
        public AllFinals() 
        { 
        } 
   } 

AllFinals.java:5: Blank final variable 'v' may not have been initialized. It must be assigned a value in an initializer, or in every constructor.
final Vector v;
but If assigned value in initializer then

import java.util.*; 
    public class AllFinals 
    { 
        { 
                final Vector v; 
                v=new Vector(); 
        } 
        public AllFinals() 
        { 
        } 
        public void someMethod() 
        { 
                System.out.println(v.isEmpty()); 
        } 
   } 

I am geting error
AllFinals.java:15: Undefined variable or class name: v
System.out.println(v.isEmpty());
^
Now
static {
final Vector v;
v=new Vector();
}
making initializer static giving the same problem why?
^
Q2 Why top level class can not be static?
Q3

//Contents of File AnInterface.java 
                public interface AnInterface 
                { 
                    public void methodOne() throws Exception; 
                } 
  
    //Contents of File AnInterfaceImpl.java 
                public class AnInterfaceImpl implements AnInterface 
                { 
                   public void methodOne() 
                    { 
                        System.out.println("I will never throw an exception"); 
                    } 
                } 
//Class ATest.java
public class ATest 
            { 
                public static void main(String args[]) 
                { 
                    AnInterface ai = new AnInterfaceImpl(); 
                    ai.methodOne(); 
                } 
            } 

here object a1 is of tyep AnInterface but reference of AnInterfaceImpl.
Call method on this object is giving compile time error methodOne do not catch or throw Exception.
But why

//Class ATest.java
              public class ATest 
             { 
                 public static void main(String args[]) 
                 { 
                    AnInterfaceImpl ai = new AnInterfaceImpl(); 
                    ai.methodOne(); 
                 } 
             } 

this compiles and with out and error or exception.
Q4
why

if(" String ".trim() == "String")
    System.out.println("Equal");
else
    System.out.println("Not Equal");

this giving not equal

[Bill Tripper]

Q1: The statement "v = new Vector()" is floating out there where your variable declarations belong. You can put it into an initializer block, e.g., "{v = new Vector();}" and it will work.
Instead of:
{
final Vector v;
v=new Vector();
}
use:
final Vector v;
{
v = new Vector();
}

[Thomas Paul]

or why not just code:
final Vector v = new Vector();
------------------
Tom - SCJP --- Co-Moderator of the Programmer Certification Forums

[Mini Pilla]

Ya this will also work or rather should.

Originally posted by Thomas Paul:
or why not just code:
final Vector v = new Vector();

[wei luo]

I think "final Vector v;
public AllFinals()
{ v = new Vector();
}
will also work.