The end is near

1
The end is near
2
Object-Oriented Design

• Methods
• Extract small parts of a program and calculations
  which will be performed multiple times
• Encapsulation
• Classes, Objects, and Polymorphism
• Covered in more detail later

3
Primitives

• int, double, boolean, float, double, char
• These are NOT Objects
• Can be compared with , !, lt, gt, etc.
• Cannot call methods
• Each primitive has an associated wrapper class
• Auto-boxing/unboxing
• Explicit type-casting needs to be done
• double?float?long?int?short?byte
• Implicit type-casting need not be done
• byte?short?int?long?float?double

4
Objects and Classes and Strings

• Objects are handled with a reference address
• Two objects should be compared with the .equals()
  method
• Do NOT use to compare objects
• Assignment operators assign references they do
  not make separate copies
• NullPointerException always make sure your
  object is not null before calling methods with it
• Constructors should be used to initialize class
  variables
• Calling methods
• Need object
• Static methods
• Can use class name
• Cannot access non-static methods/variables inside
• Pass by value always
• Keyword this

5
Objects and Classes and Strings

• Strings are a type of object
• Also should not be compared with
• Can be concatenated with the operator
• Important String functions
• charAt
• indexOf
• substring
• length

6
Selection Statements

• Modifies the flow of control of the program
• if/else construct
• Must have a boolean condition to check against
• are important, but not necessary for one line
  statements
• else branch is optional
• switch construct
• Multi-way branch which makes a decision based on
  a char, byte, short, or int
• default case
• break statement

7
Repetition Statements

• for
• while
• do-while
• Pitfalls
• Off-by-one errors
• Infinite looping
• Overflow

8
Arrays

• Linear collection of data
• Can hold primitives or Objects, but must all be
  of the same type
• length tells the number of elements in the array
• Member, not a method
• Indexed from 0 to length 1
• Protect against ArrayIndexOutOfBoundsException
• Can create multiple dimension arrays
• Usually use for-loops to iterate through members
  of the array

9
Exceptions

• Use a try/catch/finally block to handle
  exceptions thrown by a program
• Use throw statement to notify caller of an error
• Do not need to catch RunTimeExceptions
• These should be checked for instead
• User defined exceptions must extend Exception

10
File I/O

• Many classes
• FileInputStream, DataInputStream, FileReader,
  BufferedReader, Scanner, PrintWriter,
  DataOutputStream, etc.
• ObjectInputStream, ObjectOutputStream
• Used to write objects to a file
• Any object serialized by a stream must implement
  Serializable
• Which classes are used to write text and which
  are used to write binary?
• Always close files you open

11
Inheritance and Polymorphism

• Differences between abstract classes and
  interfaces
• Polymorphism can simplify code
• Extend specific classes from general classes
• Use protected keyword to protect information and
  methods
• No need to rewrite methods which are the same as
  in a parent class
• Superconstructor is always called as the first
  line of constructor

12
Dynamic Data Structures and Generics

• Inner classes
• Lists
• Node class
• Circularly linked lists
• Doubly linked lists
• Java Collections
• Vector
• ArrayList
• LinkedList

13
Recursion

• Think about what the sub-problem is
• Only be concerned with the current level of
  recursion
• Two necessary cases
• Base case
• Recursive case

14
GUI and Event-driven Programming

• Common classes
• JFrame
• JPanel
• JLabel
• JMenu, JMenuItem
• JButton
• Layouts

15
Challenges
16
What is the output?

• public class A
• private int x
• public static int doStuff()
• x 100
• x / 3
• x
• return x
• public static void main(String args)
• System.out.println(A.doStuff())

17
What is the output?

• public class A
• private int x
• public static int doStuff()
• x 100
• x / 3
• x
• return x
• public static void main(String args)
• System.out.println(A.doStuff())

Because this method is static, it does not
have access to non-static class variables. This
code will Not compile because x is non-static.
18
Types

• Given the following classes, which of the
  following declarations are valid?
• public interface I
• public interface J extends I
• public interface K
• public abstract class A
• public class B extends A implements J, K
• public class C extends B
• public class D extends A implements I
• A a new B()
• B b new J()
• C c new B()
• B b new C()
• I i new A()
• I i new B()
• I i new D()
• K k new C()

19
Types

• Given the following classes, which of the
  following declarations are valid?
• public interface I
• public interface J extends I
• public interface K
• public abstract class A
• public class B extends A implements J, K
• public class C extends B
• public class D extends A implements I
• A a new B() valid B is a subclass of A
• B b new J() invalid cannot instantiate
  interfaces
• C c new B() invalid not all B is the
  superclass of C
• B b new C() valid C is a subclass of B
• I i new A() invalid A does not implement I
• I i new B() valid A implements J, and J is a
  type of I
• I i new D() valid D impelements I
• K k new C() valid C extends B which
  implements K

20
Arrays

• Write a method which takes in an array of
  integers and replaces the values of the array
  with a value ci. Define ci to be the sum of the
  numbers in indices 0i in the incoming array.
• public void cumulativeArray(int a)

21
Arrays

• Write a method which takes in an array of
  integers and replaces the values of the array
  with a value ci. Define ci to be the sum of the
  numbers in indices 0i in the incoming array.
• public void cumulativeArray(int a)
• if (a.length lt 1)
• return
• for (int k1 klta.length k)
• ak ak ak-1

22
Linked Lists

• Given an appropriate (integer) Node class, write
  a recursive method which sums up the numbers in
  the list.
• public int sumList(Node l)

23
Linked Lists

• Given an appropriate (integer) Node class, write
  a recursive method which sums up the numbers in
  the list.
• public int sumList(Node l)
• if (l null)
• retrurn 0
• return l.num sumList(l.next)

24
Strings

• Write a recursive method reverse which takes in a
  String and returns the reverse of the String.
  You may NOT use the reverse method in the String
  class, however you may use other methods
  available to you.
• public String reverseString(String s)

25
Strings

• Write a recursive method reverse which takes in a
  String and returns the reverse of the String.
  You may NOT use the reverse method in the String
  class, however you may use other methods
  available to you.
• public String reverseString(String s)
• if (s null s.length() lt 1)
• return s
• if (s.length() 2)
• return s.charAt(1) s.charAt(0)
• return s.charAt(s.length()-1)
  reverseString(s.substring(1, s.length()-1))
  
• s.charAt(0)

26
Linked Lists

• Given an appropriate Node class, write a method
  which removes every other node from the list,
  starting with the second.
• public Node removeEveryOther(Node l)

27
Linked Lists

• Given an appropriate Node class, write a method
  which removes every other node from the list,
  starting with the second.
• public Node removeEveryOther(Node l)
• Node l1 l
• while (l1 ! null l1.next ! null)
• l1.next l1.next.next
• l1 l1.next
• return l

28
Linked Lists

• Now write the same method, but recursively.
• public Node removeEveryOther(Node l)

29
Linked Lists

• Now write the same method, but recursively.
• public Node removeEveryOther(Node l)
• // base case
• if (l null l.next null)
• return l
• // recursive case
• Node l1 removeEveryOther(l.next.next)
• l.next l1
• return l

30
Recursion

• Given an appropriate node class, write a
  recursive method which reverses a singly linked
  list.
• public Node reverse(Node l)

31
Recursion

• Given an appropriate node class, write a
  recursive method which reverses a singly linked
  list.
• public Node reverse(Node l)
• if (l null l.next null)
• return l
• Node restreversed reverse(l.next)
• l.next.next l
• l.next null
• return restreversed

32
Linked Lists

• Given an appropriate Node class, one way to
  detect a cycle in your list is by moving two
  pointers around the list, one one index at a time
  and the other two indices at a time. Write a
  method which determines whether or not there is a
  cycle in a list.
• public boolean hasCycle(Node l)

33
Linked Lists

• Given an appropriate Node class, one way to
  detect a cycle in your list is by moving two
  pointers around the list, one one index at a time
  and the other two indices at a time. Write a
  method which determines whether or not there is a
  cycle in a list.
• public boolean hasCycle(Node l)
• Node l1 l
• Node l2 l
• while (l1 ! null l2 ! null
• l1.next ! null l2.next ! null
• l2.next.next ! null)
• l1 l1.next
• l2 l2.next.next
• if (l1 l2)
• return true
• return false