Lec 7
Using Static Class Methods
Today
• We work with static utility methods of a class
• We learn how JavaDocs can help us figure out
how to use them
3 Different Kinds of Classes
1. Application Class – what we've been doing
– Has public static void main ( String [] args)
2. Instantiable Class – use to make objects from
– String, Scanner
3. Classes with only static utility methods
– like Math class
3 Different Kinds of Classes -- I
• Application Class – what we've been doing
– has public static void main(String [] args)
– where program begins execution
– where we develop solutions to lab problems
• create variables, objects that help us
• read input, compute answers, display results
3 Different Kinds of Classes -- II
• Instantiable Class – used to make objects from
– SO FAR ONLY: String, Scanner
• To use an Instantiable class we must
– Declare a variable of that class type
• String message;
Scanner myUserInput;
– Instantiate a new object
• message = new String("hello");
• myUserInput = new Scanner(System.in);
– Use associated methods (name of object '.' method)
• message.trim();
myUserInput.nextInt();
3 Different Kinds of Classes -- III
• Classes with static utility methods
– We never "instantiate" these classes
– Math class
(Math.random(), Math.round() )
– refer to the class name '.' method name
• We can get lots of help from these IF
• we learn how to read the JavaDocs manuals on them
Class NumericalStuff
• Demo "Helper" for working with numbers
– finding prime numbers, dividing
– Home made by Professor Kowalczk
• Javadocs for NumericalStuff
• Lets study some of the method
documentation:
NumericalStuff -- findPrime
• static: means it's a static utility method
– will not be associated with an object
– have to invoke by "Name of Class"
• NumericalStuff.findPrime
NumericalStuff -- findPrime
• int: means it's going to give you an integer back
– you need a variable to receive it:
• int myPrime = NumericalStuff.findPrime ...
– OR you can print it out
• System.out.println("a prime is " + NumericalStuff.findPrime... )
NumericalStuff -- findPrime
• findPrime: the name of this particular method
NumericalStuff -- findPrime
• int n: means you must give it an integer in parens
– int myPrime = NumericalStuff.findPrime (5);
– System.out.println("a prime is " +
NumericalStuff.findPrime(12));
Given this NumericalStuff method doc
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Which is/are using it correctly?
boolean x = isPrime ( 23);
int x = NumericalStuff.isPrime(23);
if (NumericalStuff.isPrime(23)){ ....
boolean x = NumericalStuff.isPrime(3.14159);
Using Class OtherStuff ...
• How would you show the current Time ?
• How would you save the 10th dictionary word?
Using Class StringUtil...
How to determine what is the 5th letter of "centaur" ?
Using Class Coin:
One other return type -- void
• Means it doesn't return anything
• Use it on a line by itself
Coin.dispenseDime(true); // prints a dime, beeps
Coin.dispenseDime(false); // prints, doesn't beep
Lab 7
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Making change with Coin Class
Ask for amount of change requested
Find how many coins that is (using Coin class)
dispense Quarters until no more left
– use a while loop with Coin.dispenseQuarters inside
• dispense Dimes until no more left
– use a while loop with Coin.dispenseDimes inside
• and so on with nickels and pennies
• maybe disable "beep" while debugging!