MethodsAbout methodsWhy methods?Defining a methodReturning a result from a methodReturning no result from a methodMethods and static methodsEscaping from staticThe EndJan 13, 2019MethodsAbout methodsA method is a named group of declarations and statementsYou execute those declarations and statements by calling the methodWhen you call the method, you can give it parameters (information, such as numbers, going into the method)A method typically has a return value (a single piece of information coming out of the method)Declarationsand statementsparameterparameterparameterreturn valueWhy methods?Methods help you break up a complex problem into simpler subproblems, which you can solve separatelyMethods can use other methods, but should not depend on the “inner workings” of those other methods--just what they do, not how they do itMethods allow you to give names to parts of your computation, thus making your program more readableReadability is essential in good programmingProper choice of method names is importantVerbs are usually best, since methods “do something”If you have anything the least bit complicated to compute, you should write (and debug) it in only one placeThis is an application of the DRY principle (“Don’t Repeat Yourself”)Methods are very good for putting code in only one placeDefining a methodA method has the syntax: return-type method-name(parameters) { method-variables code}Example: boolean isAdult(int age) { int magicAge = 21; return age >= magicAge;}Example: double average(int a, int b) { return (a + b) / 2.0;}Returning a result from a methodIf a method is to return a result, it must specify the type of the result:boolean isAdult ( …You must use a return statement to exit the method with a result of the correct type:return age >= magicAge;Returning no result from a methodThe keyword void is used to indicate that a method doesn’t return a valueThe return statement must not specify a valueExample:void printAge(String name, int age) { System.out.println(name + " is " + age + " years old."); return;}There are two ways to return from a void method:Execute a return statementReach the closing brace of the methodMethods and static methodsJava has two kinds of methods: static methods and non-static methods (also know as instance methods) However, before we can talk about what it means to be static, we have to learn a lot more about classes and objectsMost methods you write should not, and will not be staticEvery Java program has a public static void main(String[ ] args)methodThis starts us in a “static context”To “escape from static”, I recommend starting every program in a certain way, as shown on the next slideEscaping from staticclass MyClass { public static void main(String[] args) { new MyClass().run(); } void run() { // Your real code begins here }}You can replace the names MyClass and run with names of your choice, but notice that each name occurs in two places, and they have to match upThe EndThough this bemadness, yet there is methodin it. --Shakespeare,
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