1. Static Variables ICS 111: Introduction to Computer Science I
William Albritton
Information and Computer Sciences Department at the University of Hawai‘i at Mānoa
"I think there is a world market for maybe five computers.“
Thomas Watson, Chairman of IBM, 1943
11/14/2018
© 2007 William Albritton

2. Class Feedback
On an anonymous (don’t write your name) sheet of paper, answer the following questions
Average time working on each assignment
Total time studying for the exam
List several things that help you learn
List several things that make learning difficult
List several suggestions for improving the class
11/14/2018
© 2007 William Albritton

3. Using Static Variables
Static variables, or “class variables” DO NOT belong to a particular object, but are variables for the entire class
Syntax
ClassName.variableName
Examples
Static variable “out”: System.out.println(“hey”);
Static variable “in”: Scanner input = new Scanner(System.in);
11/14/2018
© 2007 William Albritton

4. Defining Static Variables
Typically, static variables of a class are constants (variables that store values that do not change), so the keyword “final” is also used in their declaration
Declaration for static variables in & out
public class System{ public static final InputStream in; public static final PrintStream out; }
11/14/2018
© 2007 William Albritton

5. Static Variables of Class Math
Class Math has useful mathematical constants (variables that store values that do not change)
Two static variables of class math
Math.E; //
Math.PI; //
Initialization (declaration & instantiation) for static variables E & PI
public class Math{ public static final Double E = new Double( ); public static final Double PI = new Double( ); }
11/14/2018
© 2007 William Albritton

6. Pinball Price Increase
The price of pinball games just went up to 50¢! We need to change our program already!
In order to make our program more adaptable, we can add constants, so that it is easier to change & maintain the program
See PinballGames.java & MyCalculator.java
11/14/2018
© 2007 William Albritton

7. Terminology
Constant
Variables that store values (data) that do not change
Makes the program more maintainable (easier to change, find & fix bugs, etc.)
Compiler will complain if try to assign a constant to another value
public class MyCalculator { public static final Integer GAME_PRICE = new Integer(50); ...}
MyCalculator.GAME_PRICE = 100; //ERROR!
11/14/2018
© 2007 William Albritton

8. Defining Static Variables
Syntax for initializing (declaring & instantiating) a static variable
Note that static variables are declared inside a class, but outside all methods
public class ClassName1 { public static final ClassName2 VARIABLE_NAME = new ClassName2(parameters); public static void method1(...){...} public static void method2(...){...} public static void method3(...){...} }
11/14/2018
© 2007 William Albritton

9. Scope of Static Variables
The scope of a variable is where a variable is visible (where it can be used)
Scope refers to a program’s line numbers in a text file
For static variables, the scope begins after the opening delimiter (curly bracket) of a class & ends at the closing delimiter (curly bracket) of a class
Scope of static variables GAME_PRICE, FREEZING, C2F_RATIO, F2C_RATIO are lines 3-47, as they can be used within any method within the MyCalculator.java program
11/14/2018
© 2007 William Albritton

10. Case Sensitive Note that Java is case sensitive
Different variables or constants for a primitive data type or object can have the same name, but different cases
Integer dollars = new Integer(10);
Integer Dollars = new Integer(20);
Integer dOlLaRs = new Integer(30);
Integer DOLLARS = new Integer(40);
11/14/2018
© 2007 William Albritton

11. Java Coding Standard
Don’t forget to include comments, especially above methods
The comments will describe what the method does, the parameters, & the return value
See link to Java Coding Standard for details
/**Calculate The Number Of Pinball Games Can Play.
dollarParameter Is The Number Of Dollars.
centParameter Is The Number Of Cents.
The Number Of Games */
public static Integer calculateGameCount(Integer dollarParameter, Integer centParameter) {...}
11/14/2018
© 2007 William Albritton

12. Class Exercise 1
Trace through the following Java program & write the output
See Exercise1.java
11/14/2018
© 2007 William Albritton

13. Terminology Class definition Client (driver)
A program that defines the static variables & static methods for a class
For example, MyCalculator.java
Client (driver)
A program that uses (tests) the class’s static variables & static methods
In other words, this program uses static variables & calls static methods & displays appropriate output
For example, PinballGames.java & TemperatureConverter.java
11/14/2018
© 2007 William Albritton

14. Class Definition & Client
Contents of a class definition
Class name at top
Static variables definitions
Static method definitions
Contents of the client (driver)
Client name at top
In main() method, use static variables
In main() method, call the static methods & display appropriate output
11/14/2018

15. Client & Class Definition
Basic outline of your assignment code
Contents of the client
Put this class at the top of your program
This class has the “public” modifier
main() method goes here
Name of class is LastNameFirstNameX
Contents of a class definition
This class does NOT have the “public” modifier
Client tells Class Definition what to do
11/14/2018
© 2007 William Albritton

16. Class Exercise 2 Write 2 Java classes For class #1 (class definition)
Store the decimal number 4.0 as a static variable
Write a Java static method that has 4 double (decimal) parameters that returns the average of the 4 doubles
For class #2 (client)
Test the method of class #1
11/14/2018
© 2007 William Albritton

17. Temperature Converter
Here is another example for declaring & using static variables
Also, check out the comments above each method formatted according to the Java Coding Standard
See TemperatureConverter.java & MyCalculator.java
11/14/2018
© 2007 William Albritton