Nothing to be happen
the program might compile the output wont come.

The constructor has the same name as that of the class to 
which it belongs to. When a return type or void is 
specified,no error occurs.It will be considered as a method.
for example:
public class myclass
{
public myclass()
...
}this is considered as a contrustor
whereas,
public class myclass
{
public void myclass()
{
...
}will be considered as a method.....

You will get a compile time error as , Construcors only 
initialize values  and does not return any thing.

simply it will considered as a normal method in the class

Answer 3 is wrong

Answer 3 is absolutely right becuse compiler strictly 
follows the syntax. Except answer 3 all are wrong.

Answer 2 is exactly correcr.I have done practiclly.No 
compile time errors.
Code will run and executes sucessfully.But it treats as 
method not as constructor.

*A constructor is a special method which has the same name  
as that of the class which is used for the initialising and 
instance,when it is being created itself.

*Normal method may or may not returns values when a normal 
method does not return value it is mentioned explicitly 
with void keyword

**ANSWER**-- 7 is write

runtime exception will be raised