1. User Defined Methods Methods are used to divide complicated programs into manageable pieces. There are predefined methods (methods that are already provided by Java) The other type are user-defined methods (methods that you create)

2. Advantages of Methods While working on one method, you can focus on just that part of the program and construct it, debug it, and perfect it. Different people can work on different methods simultaneously. If a method is needed in more than one place in a program, or in a different program, you can write it once and use it many times. Using methods greatly enhances the program’s readability because it reduces the complexity of the main method.

3. User-Defined Methods User-defined methods in Java are classified into two categories: Methods that have a type – Value-Returning Methods Methods that do not have a type, Void Methods Value-returning methods Used in expressions Calculate and return a value Can save value for later calculation or print value Void Methods Used to perform a specific task

4. Flow of Execution Execution always begins with the first statement in the method main User-defined methods execute only when called Call to method transfers control from caller to called method In method call statement, specify only actual parameters, not data type or method type Control goes back to caller when method exits

5. Construction of a Method A method must include the following: A declaration (header) An opening curly bracket A body A closing curly bracket The method declaration (header) contains: Optional access modifiers The return type for the method The method name An opening parenthesis An optional list of parameters A closing parenthesis

6. Method Headers Modifiers: public, private, protected, static, abstract, final returnType: type of value that the method calculates and returns (using return statement) OR void if no value is to be returned. The returnType can be any valid Java data type. methodName: Java identifier; name of method parameterList: Variables (primitive or reference) that are sent to the method

7. Syntax: Method modifier(s) returnType methodName(formal parameter list) { statements }

8. Syntax Parameter List When creating the parameter list you must define each variable separated by a comma. i.e. public static float age (int x, double y) return Statement Every return-type method must use the return statement to get the value back to the calling method unless it is a void method. *A return statement can return only one value. i.e return expr;

9. Syntax Argument List The argument list is the listing of values/variables in the method call. You must have the same number and type of variables in the argument listing/actual parameter listing as you have in the formal parameter listing. Method Call The method is called by using the method name followed by the argument listing/actual parameter listing. In a return type method, you must use the method call on the right hand side of and assignment statement or in some output statement. i.e. y = methodName(argument/actual parameter list)

10. Equivalent Method Definitions public static double larger(double x, double y) { double max; if(x >= y) max = x; else max = y; return max; }

11. Equivalent Method Definitions public static double larger(double x, double y) { if(x >= y) return x; else return y; }

12. Void Methods Similar in structure to value-returning methods No method type (i.e. void) Call to method is always stand-alone statement Can use return statement to exit method early

13. Void Method Example public class Banner2 { public static void main (String[] args) { printStars(); System.out.println("********** Annual ***********"); printStars(); System.out.println("******* Spring Sale **********"); printStars(); } public static void printStars() { int stars, lines; for(lines = 1; lines <= 2; lines++) { for(stars = 1; stars <= 30; stars++) System.out.print("*"); System.out.println(); }

14. Primitive Data Type Variables as Parameters A formal parameter receives a copy of its corresponding actual parameter If a formal parameter is a variable of a primitive data type Value of actual argument is directly stored Cannot pass information outside the method Provides only a one-way link between arguments and parameters

15. Scope of an Identifier Within a Class Scope (of an identifier): refers to those parts of a program where the identifier is accessible Local variables: variables declared within a method (or block) Within a class Any method can call any other method Exception: static method cannot call a nonstatic method

16. Scope Rules Identifier declared within a method is accessible Only within the method from the point at which it is declared until the end of the method By those methods nested within that method if the nested method does not have an identifier with the same name as the identifier in the outside method *Outside method: method that encloses nested block

17. Scope Rules: Demonstrated public class ScopeRules { static final double rate = 10.50; static int z; static double t; public static void main(String[] args) { int num; double x, z; char ch; //... } public static void one(int x, char y) { //... } public static int w; public static void two(int one, int z) { char ch; int a; //block three { int x = 12; //... }//end block three //... }

18. Scope Rules: Demonstrated

19. Method Overloading: An Introduction Method overloading: more than one method can have the same name Overloading Rules Every method must have a different number of parameters OR If the number of parameters is the same, then the data type of the parameter (in the order listed), must differ in at least one position Types of parameters determine which method executes