Evaluation steps:

Data: new Person( "Fred", new Person("George", new Unknown(), new Unknown()),
                                           new Person( "Emma",new Unknown(), new Unknown()) ).size()

The method size in class Unknown:
  int size() {
    return 0;
  }

The method size in class Person:
  int size() {
    return 1 + this.father.size() + this.mother.size();
  }

The steps: (when preforming these steps, you may temporarily name some of the inner portions (such as George and Emma))
 

---

new Person( "Fred", new Person("George", new Unknown(), new Unknown()),
                                           new Person( "Emma",new Unknown(), new Unknown()) ).size()

The call

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return 1 + new Person( "Fred", new Person("George", new Unknown(), new Unknown()),
                                           new Person( "Emma",new Unknown(), new Unknown()) ).father.size()
             + new Person( "Fred", new Person("George", new Unknown(), new Unknown()),
                                           new Person( "Emma",new Unknown(), new Unknown()) ).mother.size()

Substituted the Person( "Fred"...) in for this

---

return 1 + new Person("George",new Unknown(),new Unknown()).size
             + new Person( "Fred", new Person("George", new Unknown(), new Unknown()),
                                           new Person( "Emma",new Unknown(), new Unknown()) ).mother.size()

Extracted the father from Person( "Fred" )

---

return 1 +	return 1 + new Person( "George", new Unknown(),new Unknown()).father.size()               + new Person("George", new Unknown(),new Unknown()).mother.size()
	+ new Person( "Fred", new Person("George", new Unknown(), new Unknown()),                                            new Person( "Emma",new Unknown(), new Unknown()) ).mother.size()

Called size on Person("George"), substituted Person("George") in for this

---

return 1 +	return 1 + new Unknown().size()               + new Person("George", new Unknown(),new Unknown()).mother.size()
	+ new Person( "Fred", new Person("George", new Unknown(), new Unknown()),                                            new Person( "Emma",new Unknown(), new Unknown()) ).mother.size()

Extracted the father from Person("George")

---

return 1 +	return 1 + return 0 + new Person("George", new Unknown(),new Unknown()).mother.size()
	+ new Person( "Fred", new Person("George", new Unknown(), new Unknown()),                                            new Person( "Emma",new Unknown(), new Unknown()) ).mother.size()

Called size on Unknown

---

return 1 +	return 1 +  0 + new Unknown().size()
	+ new Person( "Fred", new Person("George", new Unknown(), new Unknown()),                                            new Person( "Emma",new Unknown(), new Unknown()) ).mother.size()

Extratcted the mother from Person("George")

---

return 1 +	return 1 + 0 return 0
	+ new Person( "Fred", new Person("George", new Unknown(), new Unknown()),                                            new Person( "Emma",new Unknown(), new Unknown()) ).mother.size()

Called size on Unknown

---

return 1 +	return 1 + 0 + 0
	+ new Person( "Fred", new Person("George", new Unknown(), new Unknown()),                                            new Person( "Emma",new Unknown(), new Unknown()) ).mother.size()

Finished call to size on Person("George")

---

return 1 + 1
              + new Person("Emma", new Unknown(),new Unknown()).size()

Extracted mother from Person("George")

---

return 1 + 1 +

return 1 + new Person( "Emma", new Unknown(),new Unknown()).father.size()               + new Person("Emma", new Unknown(),new Unknown()).mother.size()

Called size on Person("Emma"), substituted Person("Emma" for this

---

return 1 + 1 +

return 1 +  new Unknown().size()               + new Person("Emma", new Unknown(),new Unknown()).mother.size()

Extracted father from Person("Emma")

---

return 1 + 1 +

return 1 + return 0 + new Person("Emma", new Unknown(),new Unknown()).mother.size()

Called size on Unknown

---

return 1 + 1 +

return 1 +  0 + new Unknown().size()

Extracted mother from Person("Emma")

---

return 1 + 1 +

return 1 + 0 + return 0

Called size on Unknown

---

return 1 + 1 + 1

Finished calling size on Person("Emma")

---

return 3

Perform additions

---

3

Finished