Implementing Classes Chapter 3

What is a Java Class? A Java class describes the behaviors and attributes of an object. There are at least two java classes associated with a Java project. A class implementation .java file. This class contains instance variables and methods for accomplishing a task. A tester class .java file. The tester class instantiates an object of the class and calls the member functions described in the implementation class.

Syntax of a Java Class Declaration public class ClassName { Instance variables - data or information an object contains visible by the methods of a class. accessibility data type variable name; private double balance; Constructor methods() }

Accessibility Accessibility refers to the information or data exposure to other classes. public variables are exposed to all classes private variables are only exposed to classes to which they belong.

Method Return Types A method return type refers to how a method performs an action. A void method performs an action without storing a value. A void method does not require a return statement public void greeting()//this method simply displays text output. It does not store the outcome of a computation. { System.out.println(“Hello!”); }

Methods that return values pubic int getValue()//this method will return the information contained in a class object. { return value; Return statement }

Syntax of declaring class methods public return type method name (parameter list) {accessibility identifies the method data type of the method results.(void, int, double, string, etc) arguments- information a method needs to perform a task }

Example of a Java implementation class //This class will simulate pressing a counting device. public class Clicker{ private int value // an instance variable to store the number of clicks. public void click()// a mutator method to add 1 each time the method is called { value = value +1; } }

Clicker class continued…. //This method accesses the number of times the click method has been called. public int getValue() { return value; }

Clicker class continued... //a mutator method to reset the number of clicks stored in value back to 0. //This method does not return a value. public void reset() { value=0; }

Tester Class //This class will instantiate an object of the Clicker class and call the methods of the class. public class ClickerTester{ int numClicks(); Clicker myClicker = new Clicker(); //instantiate an object of a Clicker class. clas Object myClicker.click() // the object calls the click method. //The numClicks variable is increased by 1; System.out.println(myClicker.getValue());//displays the value of the numClicks variable myClicker.click()// another method call to the click method. }