CSE 1223 Introduction to Computer Programming in Java Chapter 5 Methods 1 Organizing Programs Consider the following issues As programs increase in complexity and size how can we break them up into more manageable pieces How can we avoid duplicating code to perform the same action in various places in our programs 2 Methods One of the mechanism provided by Java to organize program structure is static class methods Informally a method is a sequence of statements that performs some task These statements are grouped together and given a name the name of the method 3 A Simple Example Let s consider a program that after asking the user for two positive numbers width and height outputs a rectangle of s of the given width and height 4 Anatomy of a Method private static void procedureName parameters sequence of statements private static returnType functionName parameters sequence of statements return value 5 Anatomy of a Method private static void procedureName parameters sequence of statements private static returnType functionName parameters sequence of statements return value method headers 6 Anatomy of a Method private static void procedureName parameters sequence of statements private static returnType functionName parameters sequence of statements return value class static methods always start with these keywords 7 Anatomy of a Method private static void procedureName parameters this is a procedure sequence of statements it does not return a value private static returnType functionName parameters sequence of statements return value 8 Anatomy of a Method private static void procedureName parameters this is a procedure sequence of statements it does not return a value private static returnType functionName parameters sequence of statements return value this is a function it returns a value of the specified type 9 Anatomy of a Method private static void procedureName parameters sequence of statements private static returnType functionName parameters sequence of statements return value method name 10 Anatomy of a Method private static void procedureName parameters sequence of statements private static returnType functionName parameters sequence of statements return value formal parameter list 11 Anatomy of a Method private static void procedureName parameters sequence of statements private static returnType functionName parameters method bodies sequence of statements return value 12 Anatomy of a Method private static void procedureName parameters sequence of statements private static returnType functionName parameters sequence of statements return value statements executed by the method 13 Anatomy of a Method private static void procedureName parameters sequence of statements private static returnType functionName parameters sequence of statements return value return statement required in functions returns a value of the returnType statements executed by the method 14 A Method Procedure private static void outputOneRow int w formal parameter int column 0 while column w local variable System out print column column 1 System out println 15 Another Method Function private static int inputWidth Scanner in System out print Enter width 0 int width in nextInt formal parameter return width local variable 16 Parameters We need a mechanism to provide a method with the information it needs to perform its task e g What will a method to compute the area of a rectangle need What will a method to print the average of two integers need What will a method to count the number of occurrences of a character in a string need 17 Parameters cont In a method declaration we specify the formal parameter list which looks like a list of variable declarations separated by commas e g int a int b double c char d String e You can have 0 or more parameters for your methods and they can be of any data type Choose meaningful names for the formal parameters just like you would for variables 18 Examples of Method Headers private static double area double width double height private static void printAverage int x int y private static int occurrences char ch String str 19 Examples of Method Headers private static double area double width double height private static void printAverage int x int y private static int occurrences char ch String str formal parameters 20 Examples of Method Calls Scanner keyboard new Scanner System in double w keyboard nextDouble double h keyboard nextDouble double myArea area w h int i 21 j 13 printAverage i j String s This couldn t be more fun int count occurrences u s 21 Examples of Method Calls Scanner keyboard new Scanner System in double w keyboard nextDouble double h keyboard nextDouble double myArea area w h int i 21 j 13 printAverage i j actual parameters String s This couldn t be more fun int count occurrences u s 22 What Happens import java util Scanner public class ComputeArea keyboard public static void main String args w Scanner keyboard new Scanner System in h double w keyboard nextDouble double h keyboard nextDouble myArea double myArea area w h System out println myArea private static double area double width double height width double a width height return a height a 23 Procedures vs Functions Procedures are declared with void functions are declared with a return type Procedures perform an action functions compute a value Procedures do not return a value functions must return a value Procedure calls are statements function calls are expressions 24 Why Methods Methods are needed for at least two different reasons They allow us to better structure and organize our programs by breaking up possibly large pieces of code into smaller more manageable pieces When the same code solving some task appears in multiple places in our program we can write the code once in a method and execute the code in multiple places simply through a method call 25 Your Turn For each of the following tasks design an appropriate method header The task is to compute the integer average of three given integer numbers The task is to output to the screen the information of a doctor s patient given the name age weight in pounds and height in feet of the patient Given the first name middle initial and last name of a person the task is to concatenate them and return the result e g Earl E Bird 26 Your Turn cont Compute integer average of three integers Print information of patient given name age weight in pounds height in feet of patient Concatenate first name middle initial and last name of a person and return the