Create ArrayList from array using temporary object

Question

I know there are standard way by add a constructors to the class. But for classes with object superclass (has no-argument constructor) I tend to find using a temporary object simpler. Is there any down side for such an act.

    import java.util.ArrayList;
    public class Main { 

      public static void main(String[] args){

        // data available in two separated arrays  
        String[] dName = {"Sam","Ben","Joye","Sarah","Tim","Lucy","Jack"} ;
        int[] dAge= {10,52,53,15,12,60,21};

        // Array list to put the data in 
        ArrayList<Person> personList =new ArrayList<Person>(7);

        for (int i=0;i<dName.length;i++){
            Person tempPerson = new Person();
            tempPerson.name= dName[i];
            tempPerson.age= dAge[i];
            personList.add(new Person());
            personList.set(i,tempPerson);
            tempPerson=null;    //removes the reference
        }

        for (int j=0 ; j<personList.size();j++){
            System.out.println(personList.get(j).name+" age is "+personList.get(j).age );
        }

      }  
    }

class Person{
    String name;
    int age;
}

the output

Sam age is 10
Ben age is 52
Joye age is 53
Sarah age is 15
Tim age is 12
Lucy age is 60
Jack age is 21

Answer 1

You should avoid statements that do nothing - an optimization would be to do

   for (int i=0;i<dName.length;i++){
        Person tempPerson = new Person();
        tempPerson.name= dName[i];
        tempPerson.age= dAge[i];
        personList.add(tempPerson);
    }

• No need to first add the person to later replace it
• No need to null the reference - the list will keep the reference to the temp object in any case.
• Instead of setting values directly you could use setters ( setName() instead of .name = )
• If you'd use setters, you could implement a Builder pattern:

like this:

 public Person setName(String aName) {
   name = aName;
   return this;
 }

Resulting in something like

 personList.add(new Person().setName(dName[i]).setAge(dAge[i]));

Then again - the two value constructor will probably be the easiest of all - and it don't matter that the super class doesn't have a constructor:

public Person(String aName, int aAge) {
   name = aName;
   age = aAge;
}
//You can have more than one constructor
public Person() {
}

and then

personList.add(new Person(dName[i], sAge[i]));

Answer 2

You should use a constructor for Person. Then you have just one call in your for-loop:

personList.add(new Person(dName[i], dAge[i])

Also, in your implementation, you are doing the necessary work twice, because you call personList.add(new Person()) and then you call personList.set(i, temPerson) . If you don't want a constructor in your Person-class, a call of personList.add(tempPerson) for example would be enough.

Answer 3

Not really,

you could maybe make use of java8 streams, but why make your life harder, it wouldnt add anything new