CIS 234: Java Methods Dr. Ralph D. Westfall April, 2010

What is a Method? a block of code that does something has a name and parentheses after name curly brackets enclose statement(s) in body usually has header declarations, and often has arguments inside the parentheses public static void main (String [] args) { System.out.println("Hi!"); }

Declarations - type of access modifiers before method name public – any other class can use method main method must be public private – only methods in same class can use it can leave out the access modifier defaults to friendly – can be used by other classes in same "package" (a package is somewhat like a directory)

Declarations - static static means unchanging all objects created from this class will use this same method there will not be additional copies of a static class method if don't use word static, each object created from this class will have its own instance (copy) of method

Declarations – void or [type] return value type void means doesn't return any data if not void, need to identify the type of data the method will return public static long cubeIt(int x) // int arg { // returns a long integer return x * x * x; }

Arguments (args) the parentheses often enclose "argument(s)" (data) that the method uses, identified by data type public void say(String what) // argument { System.out.println(what); // used here } // from Hello, world! Person class codeHello, world!

Arguments - 2 Java is "strongly typed," so the data type of every variable must be declared somewhere in a Java class argument data types are declared within method's parentheses public static double raised(int salary, double pct) { return (100 + pct) / 100.0) * salary; }

Calling a Method from within its class method name([arguments, if has any]) ; say("Hi!"); // literal argument from another object or classclass [object].[method name]([arguments]) ; myObject.cube(num); // variable argument myObject.raised(empSalary, 5); //both types Math.sqrt(4); // literal in a class method

Calling a Method - 2 arguments must be in right order static double raise(double salary, double pct) raise (wages, increase) ; // correct order raise(7, 50000) ; // logical error argument names don't need to match myObject.raise(pay, increase) ; // declared in method as // (double salary, double pct)

"Signature" a method's "signature" is a pattern: number, order, and types of arguments can have 0 [called with [name]( );] to many an "overloaded" method has more than one signature e.g., can be called with different patterns of arguments: (); (int x); (int x, double y); (int x, char y);

Types of Java Programs applications class that can run without any other programs (often used with other classes) class(es) that doesn't run by itself, but is used by another application class applet class runs inside a web browser (the browser actually is a program) // [PgDn] class

Types of Java Programs - 2 servlet runs on a server and makes it possible to generate web pages with database content programmer can create a Java Server Page (JSP), which then gets compiled into a servlet (Blackboard pages are servlets) servlets are part of the Java Enterprise Edition (JDK + Java EE bundle)JDK + Java EE bundle

Main Method one class in a Java application must have a main( ) method but a class used by an application doesn't need a main( ) method main method must be declared as: public static void

Main Method - 2 main method runs first when application starts it can call methods in its own class, and/or use methods in other classes methods it calls in its own class must be static variables that are not inside any method in the class must also be static

Main Method - 3 main method has String[ ] argument(s) means that you can "pass" one or more words as inputs into class when you run it public class MyProgram { public static void main (String[ ] args) [in DOS after class has been compiled] C:\>[path] java MyProgram Le 19 // 2 args

Using Extra Methods in a Class saves typing (or pasting) can use a separate method, rather than keep repeating same block of code in main method makes code easier to read and maintain smaller programs code is organized into blocks //Notes Page

Exercise following pattern in DemoMethods.java, fill in the blanks in the handout to:DemoMethods.java declare 3 numbers and one String as member variables (above main method), using meaningful variable names assign values to three of these variables in the loadData method (leave one of the numeric variables without a value

Exercise (part 2) following pattern in DemoMethods.java, write the following 4 methods:DemoMethods.java print a literal value with say( method add 2 numbers together and store them in a member variable (above main method) print this calculated member variable multiply two numbers and print result with some identifying text