Arrays of Objects

Goals

• Practice creating, traversing, and performing operations on arrays of objects.
• Learn how to write/use methods that take an array of objects as an argument
• Learn how to write/use method that return an array of objects.
• Learn that when an array is passed to a method, a reference is passed, which means that the method can change the array.
• Do error checking for invalid inputs esp. if input is an array.

Part 1: Complete the Person Database class (File: Person.java, PersonDB.java)

• Person.java which is complete.
• PersonDB.java which contains "skeleton code".
• db.hist a DrJava history file with sample interactions

1. printDB method prints all the entries in the Person database. This method is completed for you.

   >PersonDB people = new PersonDB();  
   >people.printDB()
   Name	Age
   jo	25
   flo	18
   mo	19
   
       

2. Complete the getAverageAge(...) method. Note that although this method is a "getter" there is no corresponding instance variable.

   > PersonDB people = new PersonDB();
   > people.getAverageAge()
   20.666666666666668

3. Add a constructor which has one argument: an array of Persons.
   Sample Interactions:

   > Person[] kids = {new Person("al",2), new Person("sal",4), new Person("val",6)};   
   > PersonDB kidDB = new PersonDB(kids);
   > kidDB.printDB()
   Name	Age
   al	2
   sal	4
   val	6
       
   > kidDB.getAverageAge()    
   4.0    
   

4. Complete the isInDatabase(...) method
   In this method, two Strings need to be compared to see if they are equal. However if the == operator is used, Java compares the addresses where the String objects are stored, not the letters in the String. Use the String class' equals or equalsIgnoreCase method to compare two Strings for equality. Here is String class documentation. For example:
   Sample Interactions:

   > PersonDB people = new PersonDB();
   > people.isInDatabase("flo")
   true
   > people.isInDatabase("rex")
   false
   > people.isInDatabase("moses")
   false
   > people.isInDatabase("mo")
   true
   > Person[] kids = {new Person("al",2), new Person("sal",4), new Person("val",6)};   
   > PersonDB kidDB = new PersonDB(kids);
   > kidDB.isInDatabase("valerie")    
   false    
   > kidDB.isInDatabase("s")    
   false    
   > kidDB.isInDatabase("sal")    
   true
   

5. Add methods getOldest and getYoungest, which return the oldest and youngest person in the database. Make sure you use the correct return type. Note that the interactions below call the getName() method so that we can see the name of the Person being returned. The interactions are as follows:
   Sample Interactions:

   > Person[] kids = {new Person("al",2), new Person("sal",4), new Person("val",6)};   
   > PersonDB kidDB = new PersonDB(kids);
   > PersonDB people = new PersonDB();
   > people.getOldest().getName()   
   "jo" 
   > people.getYoungest().getName()   
    "flo"  
   > kidDB.getOldest().getName()    
   "val"  
   > kidDB.getYoungest().getName()
   "al"