More on Classes

1
More on Classes Arrays

• Pepper
• With help from
• http//docs.oracle.com/javase/tutorial/java/IandI/
  super.html

2
Review - A Class Trace Exercise

• What's wrong with the following program?
• public class SomethingIsWrong public
  static void main(String args)
  Rectangle myRect myRect.width
  40 myRect.height 50
  System.out.println ("myRect's
  area is " myRect.area())
• http//docs.oracle.com/javase/tutorial/java/javaOO
  /QandE/objects-questions.html

3
Class Extension

• Make sub-classes (put "extends " classname after
  class)
• http//home.adelphi.edu/pe16132/csc171/notes/fang
  stuff/Wackadot.java
• Can use the entire extended class
• Can override methods
• This is how we use Fang's game class
• Can see all protected and public methods and
  variables

4
Class Extension - Super

• Can choose to execute methods from the super
  class using super.methodname
• http//docs.oracle.com/javase/tutorial/java/IandI/
  super.html

5
Player Extension

• Make one player
• Extend to different player types
• Example
• http//home.adelphi.edu/pe16132/csc171/notes.html

6
Abstraction

• If you know you will make a lower class, you
  don't have to implement all methods
• You can mark a class as abstract (public abstract
  class) and then put only the method headers.
  Compiler complains if the lower class does not
  implement it.
• http//docs.oracle.com/javase/tutorial/java/IandI/
  abstract.html

7
Interface

• Can create a type that has only abstract methods.
  
• Basically a contract to implement interfaces
• Contains method headers with no code below it.
• Lower classes can implement many interfaces (but
  only extend one class)
• Implementing an interface means you promise (and
  the compiler checks) that you will implement the
  methods listed.
• http//docs.oracle.com/javase/tutorial/java/IandI/
  interfaceDef.html

8
More on Arrays For Each

• Shortcut for loop through an array
• for (variable to hold value array name)
• Ex
• int arr 1,2,3,4int tot 0for (int x
  arr) tot tot xSystem.out.println(tot)

9
ArrayList

• An Array class
• Has methods you can use
• Can make an array of anything using lttypegt
• ArrayListltStringgt myArr new ArrayListltStringgt()
  
• ArrayListltPlayergt guys new ArrayListltPlayergt()
  
• http//www.anyexample.com/programming/java/java_ar
  raylist_example.xml

10
ArrayList Methods

• Methods
• add( Object o ) - puts reference to object into
  ArrayList
• get( int index ) - retrieves object reference
  from ArrayList index position
• size() - returns ArrayList size
• remove( int index ) - removes the element at the
  specified position in this list. Shifts any
  subsequent elements to the left and returns the
  element that was removed from the list.
• indexOf( Object o) - finds the index in this list
  of the first occurrence of the specified element
• clear() - removes all of the elements

11
ArrayList of Players

• guys.add(new Player("Amy"))guys.add(new
  Player("Jim"))
• guys.