Methods

A Deeper Look

Chapter 6

What is in this chapter

· Program modules

· Static methods and fields

· The Math class

· Methods with multiple parameters

· String Concatenation

· Ways to call methods

· The Call Stack & Activation Records

· The Java API Package

· Random-Number Generation

· Declaring constants

· Enumerations

· Scope

· Method Overloading

Program Modules

• Software engineering is a whole branch of computer science that studies how to make writing programs easier and more error free.

• One of the tenets of software engineering is that program that are modular are easier to write, to modify, and to reuse

Design using modules

• If the problem is very large, it should be broken down into modules.

– A module should be a self-contained unit of code.

– It should be as independent as possible, with an interface that communicates with other modules.

– Each module should perform a well defined task

– It can be developed in isolation from the rest of the program

Writing modules

• Abstraction and information hiding

– When you break a problem down into modules, each module should be a “black box”

• The other modules need to know what goes into the box, and what comes out (the public part), but do not need to know HOW the transformation took place

• This does several things:

– It frees the other modules from having to know and understand what went on in the other “black boxes”

– It means the writer of each “black box” has to concentrate only on how their box works

– It means the inside of the box (the private part) cannot be tinkered with by someone else.

Program modules in Java

• Three kinds of modules exist in Java

– Methods

– Classes

– Packages

The Math class

• The Math class contains many common math functions

• They all have two things in common

– All return a value and

– All are called with Math.methodName()

• Included are all the trig functions

– Ceiling, floor, max, min, pow, sqrt

• A look at the Math class in the Java API

• Also included are two constants, PI and E

• To use them, you must include the class name

• Math.PI or Math.E

Writing and calling methods

• Writing the method involves both the header and body

– Header:  returnType methodName (argument types)
Body:  this is the Java implementation

– Example:  double add(double num1, double num2)
                 {     double result = num1 + num2:
                        return result;
                  }

– result is a local variable, since it is defined inside the body of the method

• The method call is the method name, and actual arguments

– double number1 = 8.8, number2 = 5.5, sum;
sum = add(number1, number2);.

There are three ways to call a method

• Use the method name by itself to call another method of the same class

• If the method was part of an encapsulated class, call it with an object in front of a dot

• Use the class name if it is a static method like those in the Math class

Example from the text

• Look at MaximumFinder on overhead

• This is a complete class, with a method called in the class