Inner Class - Order of Print Statements -

Question

I'm puzzled as to why my program prints statements in a certain order?

I have a Student class , inside which is an Inner Class of Address . The idea of the program is to first assign a Home Address to a Student Object, but then also assign a University / Term Time Address by utilizing the Inner Address Class.

The code is as follows:

Student Class (with Inner Address Class)

 public class Student {

    private String name;
    private Address homeAddress, uniAddress;

    public Student(String name, int houseNumber, String homeStreet) {
        this.name = name;
        homeAddress = new Address(houseNumber, homeStreet);
    }

    public String getName() {
        return name;
    }

    public Address getHomeAddress() {
        String s = "n/a";

        if (homeAddress != null) {
            return homeAddress;
        } else {
          //  System.out.println(s);
            return null;
        }


    }

    public void setUniAddress(int num, String add) {

        uniAddress = new Address(num, add);
    }

    public Address getUniAddress() {

        String s = "n/aa";

        //If uniAddress isn't set, 
        // then "n/aa" gets printed before anything else i/e toString() method - WHY?

        if (uniAddress == null) {
           System.out.println(s);
            return null;
        } else {

            return uniAddress;
        }
    }

    @Override
    public String toString() {

        return "NAME: " + getName() + "\n"
             + "HOME ADDRESS: " + getHomeAddress() + "\n"
             + "TERM TIME ADDRESS: " + getUniAddress();

    }

    // Inner Class
    public class Address {

        private int number;
        private String street;

        public Address(int no, String street) {
            number = no;
            this.street = street;
        }

        @Override
        public String toString() {
            //return name + "\n" + number + " " + street;
            return number + " " + street;
        }
    }
}   // more Student methods .. }

The TestStudent Class (with main method)

  public class TestStudent {

    public static void main(String[] args) {
        //Home Address
        Student s1 = new Student("Cathy", 21, "Smithfield Drive");
        //Uni Address
        s1.setUniAddress(72, "Nottingham Drive");



        Student.Address anotherAddress = s1.new Address(8, "Deerfield Way");
        // note the use of new

        System.out.println(s1.toString());


    }
}

The output is:

n/aa
NAME: Cathy
HOME ADDRESS: 21 Smithfield Drive
TERM TIME ADDRESS: null

(all on new lines)

If I do not assign a Uni Address to the Student (ie If I comment out the appropriate line in the main method - that calls the setUniAddress() method), I am curious then, as to why 'n/aa' from the getUniAddress() method is printed before the toString() method? (as above)

If I do call the setUniAddress() method the out put is:

NAME: Cathy
HOME ADDRESS: 21 Smithfield Drive
TERM TIME ADDRESS: 72 Nottingham Drive

(all on new lines)

Which seems to work as intended.

I'm also wondering how, instead of printing 'null' to the TERM TIME ADDRESS : (when setUniAddress() method isn't called), I could return the 'n/aa' in it's place - that is what I was attempting to do?

Thanks.

Answer 1

1. getUniAddress() is called from the toString() which is why the n/aa is printed first.

2. If you want to print "n/aa" as a default value - set it as a default value, for example, change the declaration to:

   private Address homeAddress, uniAddress = "n/aa";

---

@Override
public String toString() {

return "NAME: " + getName() + "\n"
     + "HOME ADDRESS: " + getHomeAddress() + "\n"
     + "TERM TIME ADDRESS: " + getUniAddress(); // <-- here you call getUniAddress() which 
                                                // is why "n/aa" is printed first

}

in getUniAddress() you have the following line which prints "n/aa":

System.out.println(s);

Answer 2

When the return statement in the toString() method is executed the get*() methods are called. Then a string is created and returned by the toString() method.

So the 'n/aa' is printed while calculating the string to return from the toString(), then the toString() method returns the string and the main method prints the output generated from toString().