Can an instance complete its arguments later?

Question

I wonder if there is any way that I can declare a new instance with parameters, do not fill them, and just set them later.

Here is an example:

private Example example = new Example() // Need 1 parameter.

public void foo(Object arg1)
{
   example = new Example(arg1);
}

It is clear that this is not possible, but is there a way to do something similar to that?

score 2 · Accepted Answer · answered Nov 02 '14 at 11:52

2

You can always use a parameter-less constructor, and then set the properties of the created instance later.

....
public Example ()
{
    this.s = null;
}

public Example (String s)
{
    this.s = s;
}
....
public void setS (String s)
{
    this.s = s;
}
....
Example ex = new Example ("something");
Example ex2 = new Example ();
ex2.setS("Something Else");

answered Nov 02 '14 at 11:52

Eran

387,369
54
702
768

*You can always use a parameter-less constructor* only if such constructor is defined by you or automatically by the compiler. – Luiggi Mendoza Nov 02 '14 at 11:55
@LuiggiMendoza Fair enough. I was assuming that class is under the control of the OP, so they can add whatever constructor they need. – Eran Nov 02 '14 at 11:56
Seems promising, thanks! Accepting answer in 6 minutes. – Thanos Paravantis Nov 02 '14 at 11:57

score 0 · Answer 2 · answered Nov 02 '14 at 11:55

0

public class Example{
   private Object object1;
   public Example(){ 

   }

   public void setObject1(Object o){
      this.object1 = o;
   }
}

Now you can use this as follows:

Example example = new Example();
example.setObject1(someObject);

answered Nov 02 '14 at 11:55

Salih Erikci

5,076
12
39
69

score 0 · Answer 3 · answered Nov 02 '14 at 12:06

As noted by others and yourself already, there is no easy / official way of object construction when you can't provide the parameters needed.

You may want to look at the Objenesis project. They provide clever ways of instantiation of objects in non-standard ways. To my knowledge sometimes being able to instantiate objects without providing the usually mandatory arguments declared by the constructors.

Can an instance complete its arguments later?

3 Answers3