Computer programming 2 Lesson 3

Computer programming 2 Lesson 3

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  Computer Programming 2 Lesson 3–OBJECT AND CLASSES Prepared by: Analyn G. Regaton
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  OBJECTAND CLASSES  Object −have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors – wagging the tail, barking, eating. An object is an instance of a class.  Class − A class can be defined as a template/blueprint that describes the behavior/state that the object of its type support.
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  OBJECTS IN JAVA  Softwareobjects also have a state and a behavior. A software object's state is stored in fields and behavior is shown via methods.  So in software development, methods operate on the internal state of an object and the object- to-object communication is done via methods.
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  CLASSES IN JAVA A classis a blueprint from which individual objects are created. Following is a sample of a class. Example public class Dog { String breed; int age; String color; void barking() { } void hungry() { } void sleeping() { } } OBJECTS CLASS
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  CLASSES IN JAVA  Aclass can contain any of the following variable types.  Local variables − Variables defined inside methods, constructors or blocks are called local variables. The variable will be declared and initialized within the method and the variable will be destroyed when the method has completed.  Instance variables − Instance variables are variables within a class but outside any method. These variables are initialized when the class is instantiated. Instance variables can be accessed from inside any method, constructor or blocks of that particular class.  Class variables − Class variables are variables declared within a class, outside any method, with the static keyword.
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  CONTRUCTORS Each time anew object is created, at least one constructor will be invoked. The main rule of constructors is that they should have the same name as the class. A class can have more than one constructor. Following is an example of a constructor − public class Puppy { public Puppy() { } public Puppy(String name) { // This constructor has one parameter, name. } }
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  CREATINGAN OBJECT A class providesthe blueprints for objects. So basically, an object is created from a class. In Java, the new keyword is used to create new objects. There are three steps when creating an object from a class −  Declaration − A variable declaration with a variable name with an object type.  Instantiation − The 'new' keyword is used to create the object.  Initialization − The 'new' keyword is followed by a call to a constructor. This call initializes the new object.
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  EXAMPLE public class Puppy { publicPuppy(String name) { // This constructor has one parameter, name. System.out.println("Passed Name is :" + name ); } public static void main(String []args) { // Following statement would create an object myPuppy Puppy myPuppy = new Puppy( "tommy" ); } } If we compile and run the above program, then it will produce the following result − Output Passed Name is :tommy