Announcements
• Final Exam: TBD
Static Variables and Methods
• static means “in class” methods and variables
• static variable: one per class (not one per object)
• static method: no invoking object (invoke with
className.method())
• Example: Math class methods
threeToFifth = Math.pow(3.0, 5.0);
Static Variable Example
public class MyClass {
…
private final int STARTID = 1;
//the following are one per object
private int IDNum = -1;
//the following are one per class
private static int nextIDNum = STARTID;
public MyClass()
{
…
IDNum = nextIDNum;
nextIDNum++;
}
Client Program for MyClass
public static void main(String [] args)
{
…
myClass first = new myClass(); //IDNum is 1
myClass second = new myClass(); //IDNum is 2
}
Static Method Example
public class MyClass {
…
private final int STARTID = 1;
//the following are one per object
private int IDNum = -1;
//the following are one per class
private static int nextIDNum = STARTID;
…
public static int GetNextID()
{
// Called by MyClass.GetNextID()
return nextIDNum;
}
}
Client Program for MyClass
public static void main(String [] args)
{
…
myClass first = new myClass(); //IDNum is 1
myClass second = new myClass(); //IDNum is 2
System.out.println(“Next ID Num is:” +
MyClass.GetNextID()); //Displays ID 3
}
Other Class Methods
• boolean equals( objType comObj)
– compares invoking object with passed object
– Returns true if both are “equal”, false if not
• void display()
– Displays attributes
• String toString()
– Converts all attributes to String and returns String
public class MyClass {
…
private final int STARTID = 1;
//the following are one per object
private int IDNum = -1;
//the following are one per class
private static int nextIDNum = STARTID;
…
public boolean equals(MyClass compare)
{
if (IDNum == compare.IDNum)
return true;
else
return false;
}
}
Project
• Turn in to TA
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.java File for main()
.java File for class
.doc “What I learned” file
.txt Data File
• Confirm that TA Received Your Program
• No Late Projects Accepted!
Documentation
• Comments:
– Document Approach to Problem
• Outline Design Above main() and class
• Briefly Describe Methods
– Comment Any Unobvious Code
• Analysis:
– What Did You Learn from the Project?
– What Went Wrong? What Went Right?
– What Would You Do Differently?
Final Exam
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2 Hours
200 Points
30% of Grade
Must Take to Pass Course
Need to Know for Final
• Everything Through Exam 2
• Plus:
– Passing Arrays to Methods
– Array Initialization
– Classes
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Constructors
Accessor Methods
Mutator Methods
toString() and equals() Methods
Final Exam
• 200 Points Total – 30% of Final Grade
• 90 points Matching or Short Answer or
Multiple Choice (Terminology, Operators,
JAVA Basics)
• 30 Points Program Output
• 80 Points Programming (Full Programs)
Final Exam
• Study Previous Exams and Quizzes
• Make Sure to Study Arrays, and Classes
• Have fun 8) !!
What Have You Learned?
• Logical Thinking, Design, Planning
• “Real World” Issues (Users, Run-time problems,
“off-by-one”, Commenting, etc.)
• Programming:
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Variables
Constants
Selection
Iteration
Files
Methods
Classes
Future
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cs116
Data Structures (lists, stacks)
Searching and sorting
Classes
– Inheritance
– Encapsulation
– Templates