1. 26-Jun-15 Methods

2. About methods A method is a named group of declarations and statements You execute those declarations and statements by calling the method When 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) Declarations and statements parameter return value

3. Why methods? Methods help you break up a complex problem into simpler subproblems, which you can solve separately Methods can use other methods, but should not depend on the “inner workings” of those other methods--just what they do, not how they do it Methods allow you to give names to parts of your computation, thus making your program more readable Readability is essential in good programming Proper choice of method names is important Verbs 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 place This is an application of the DRY principle (“Don’t Repeat Yourself”) Methods are very good for putting code in only one place

4. Defining a method A 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; }

5. Returning a result from a method If 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 ;

6. Returning no result from a method The keyword void is used to indicate that a method doesn’t return a value The return statement must not specify a value Example: 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 statement  Reach the closing brace of the method

7. Methods and static methods Java 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 objects Most methods you write should not, and will not be static Every Java program has a public static void main(String[ ] args) method This starts us in a “static context” To “escape from static”, I recommend starting every program in a certain way, as shown on the next slide

8. Escaping from static class 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 up

9. The End Though this be madness, yet there is method in it. --Shakespeare, Hamlet