Question

In terms of garbage collection within Java (any version) are these two code blocks equivalent as to when they will become eligible:

public class Foo  
{  

    public Foo()  
    {  
        go();   
    }  

   public List go()  
    {  
       List things = new List();  
        things.add(42);  
        things.add(new Object());
        return things;
    }  
} 

and the following:

public class Foo  
    {   
        public Foo()  
        {     
        }  

        public List go()  
        {  
           List things = new List();  
            things.add(42);  
            things.add(new Object());
            return things;
        }  
    } 

The question I have is the following:

Does a function invoked from a constructor cause the garbage collector to ignore any objects that are scoped within that function if they were invoked from a constructor?

Answer 1

In your first class go() is called from the constructor. Until the line of code : go() is called, nothing exists for that object but a space in memory pointed to by the variable that the object was instantiated to. At the time go() is called, a new list is created in memory, things are added and the list is returned. Unless that list returned was saved to a variable somewhere it is garbage. The method remains as an instance method of the object but the returned list object is now gone.
Your second example does the same thing as the first one except the constructor is not calling the method go(). The method still exists as an instance method of the object, but the list object was never created.
So once the first example exits the method go(), the first example is in the same state of rest as the second example would be upon creation. Both ready to create and return a list with their own method, but neither having a list or memory for one allocated yet. It is up to the garbage collector WHEN the list in the first example will be actually collected, but it has been marked as garbage (unless saved to a variable somewhere in code not seen in the examples).