Advanced Programming Language - Chapter II: Objects - Oriented Programming

as follows: public boolean equals(Object obj) { return (this == obj); } For example, the equals method is overridden in the Circle class. public boolean equals(Object o) { if (o instanceof Circle) { return radius == ((Circle)o).radius; } else return false; } Optional Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 92 NOTE The == comparison operator is used for comparing two primitive data type values or for determining whether two objects have the same references. The equals method is intended to test whether two objects have the same contents, provided that the method is modified in the defining class of the objects. The == operator is stronger than the equals method, in that the == operator checks whether the two reference variables refer to the same object. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 93 The hashCode() method Invoking hashCode() on an object returns the hash code of the object. Hash code is an integer, which can be used to store the object in a hash set so that it can be located quickly. Hash sets will be introduced in Chapter 22, “Java Collections Framework.” The hashCode implemented in the Object class returns the internal memory address of the object in hexadecimal. Your class should override the hashCode method whenever the equals method is overridden. By contract, if two objects are equal, their hash codes must be same. Optional Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 94 The finalize, clone, and getClass Methods The finalize method is invoked by the garbage collector on an object when the object becomes garbage. The clone() method copies an object. The getClass() method returns an instance of the java.lang.Class class, which contains the information about the class for the object. Before an object is created, its defining class is loaded and the JVM automatically creates an instance of java.lang.Class for the class. From this instance, you can discover the information about the class at runtime. Optional Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 95 The finalization Demo The finalize method is invoked by the JVM. You should never write the code to invoke it in your program. For this reason, the protected modifier is appropriate. Optional FinalizationDemo Run Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 96 Hiding Fields and Static Methods You can override an instance method, but you cannot override a field (instance or static) or a static method. If you declare a field or a static method in a subclass with the same name as one in the superclass, the one in the superclass is hidden, but it still exists. The two fields or static methods are independent. You can reference the hidden field or static method using the super keyword in the subclass. The hidden field or method can also be accessed via a reference variable of the superclass’s type. Optional Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 97 Hiding Fields and Static Methods, cont. When invoking an instance method from a reference variable, the actual class of the object referenced by the variable decides which implementation of the method is used at runtime. When accessing a field or a static method, the declared type of the reference variable decides which method is used at compilation time. HidingDemo Run Optional Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 98 Initialization Block Initialization blocks can be used to initialize objects along with the constructors. An initialization block is a block of statements enclosed inside a pair of braces. An initialization block appears within the class declaration, but not inside methods or constructors. It is executed as if it were placed at the beginning of every constructor in the class. public class Book { private static int numOfObjects; private String title; private int id; public Book(String title) { numOfObjects++; this.title = title; } public Book(int id) { numOfObjects++; this.id = id; } } public class Book { private static int numOfObjects; private String title private int id; public Book(String title) { this.title = title; } public Book(int id) { this.id = id; } { numOfObjects++; } } Equivalent Optional Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 99 Static Initialization Block A static initialization block is much like a nonstatic initialization block except that it is declared static, can only refer to static members of the class, and is invoked when the class is loaded. The JVM loads a class when it is needed. A superclass is loaded before its subclasses. InitializationDemo Run Optional Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 100 Inheriting GUI Components Objective: Create a custom frame by extending JFrame. CustomFrame Run Optional GUI Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 ABSTRACT CLASSES AND INTERFACES 101 Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 102 The abstract Modifier The abstract class – Cannot be instantiated – Should be extended and implemented in subclasses The abstract method – Method signature without implementation Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 103 GeometricObject -color: String -filled: boolean -dateCreated: java.util.Date +GeometricObject() +getColor(): String +setColor(color: String): void +isFilled(): boolean +setFilled(filled: boolean): void +getDateCreated(): java.util.Date +toString(): String The color of the object (default: white). Indicates whether the object is filled with a color (default: false). The date when the object was created. Creates a GeometricObject. Returns the color. Sets a new color. Returns the filled property. Sets a new filled property. Returns the dateCreated. Returns a string representation of this object. Circle -radius: double +Circle() +Circle(radius: double) +getRadius(): double +setRadius(radius: double): void +getArea(): double +getPerimeter(): double +getDiameter(): double Rectangle -width: double -height: double +Rectangle() +Rectangle(width: double, height: double) +getWidth(): double +setWidth(width: double): void +getHeight(): double +setHeight(height: double): void +getArea(): double +getPerimeter(): double Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 104 Abstract Classes GeometricObject Circle Rectangle GeometricObject -color: String -filled: boolean -dateCreated: java.util.Date #GeometricObject() +getColor(): String +setColor(color: String): void +isFilled(): boolean +setFilled(filled: boolean): void +getDateCreated(): java.util.Date +toString(): String +getArea(): double +getPerimeter(): double Circle -radius: double +Circle() +Circle(radius: double) +getRadius(): double +setRadius(radius: double): void +getDiameter(): double Rectangle -width: double -height: double +Rectangle() +Rectangle(width: double, height: double) +getWidth(): double +setWidth(width: double): void +getHeight(): double +setHeight(height: double): void The # sign indicates protected modifer Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 105 NOTE An abstract method cannot be contained in a nonabstract class. If a subclass of an abstract superclass does not implement all the abstract methods, the subclass must be declared abstract. In other words, in a nonabstract subclass extended from an abstract class, all the abstract methods must be implemented, even if they are not used in the subclass. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 106 NOTE An abstract class cannot be instantiated using the new operator, but you can still define its constructors, which are invoked in the constructors of its subclasses. For instance, the constructors of GeometricObject are invoked in the Circle class and the Rectangle class. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 107 NOTE A class that contains abstract methods must be abstract. However, it is possible to declare an abstract class that contains no abstract methods. In this case, you cannot create instances of the class using the new operator. This class is used as a base class for defining a new subclass. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 108 NOTE A subclass can be abstract even if its superclass is concrete. For example, the Object class is concrete, but its subclasses, such as GeometricObject, may be abstract. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 109 NOTE A subclass can override a method from its superclass to declare it abstract. This is rare, but useful when the implementation of the method in the superclass becomes invalid in the subclass. In this case, the subclass must be declared abstract. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 110 NOTE You cannot create an instance from an abstract class using the new operator, but an abstract class can be used as a data type. Therefore, the following statement, which creates an array whose elements are of GeometricObject type, is correct. GeometricObject[] geo = new GeometricObject[10]; Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 111 Example: Using the GeometricObject Class Objective: This example creates two geometric objects: a circle, and a rectangle, invokes the equalArea method to check if the two objects have equal area, and invokes the displayGeometricObject method to display the objects. TestGeometricObject Run Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 112 The Abstract Calendar Class and Its GregorianCalendar subclass java.util.GregorianCalendar +GregorianCalendar() +GregorianCalendar(year: int, month: int, dayOfMonth: int) +GregorianCalendar(year: int, month: int, dayOfMonth: int, hour:int, minute: int, second: int) Constructs a GregorianCalendar for the current time. Constructs a GregorianCalendar for the specified year, month, and day of month. Constructs a GregorianCalendar for the specified year, month, day of month, hour, minute, and second. The month parameter is 0-based, that is, 0 is for January. java.util.Calendar #Calendar() +get(field: int): int +set(field: int, value: int): void +set(year: int, month: int, dayOfMonth: int): void +getActualMaximum(field: int): int +add(field: int, amount: int): void +getTime(): java.util.Date +setTime(date: java.util.Date): void Constructs a default calendar. Returns the value of the given calendar field. Sets the given calendar to the specified value. Sets the calendar with the specified year, month, and date. The month parameter is 0-based, that is, 0 is for January. Returns the maximum value that the specified calendar field could have. Adds or subtracts the specified amount of time to the given calendar field. Returns a Date object representing this calendar’s time value (million second offset from the Unix epoch). Sets this calendar’s time with the given Date object. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 113 The Abstract Calendar Class and Its GregorianCalendar subclass An instance of java.util.Date represents a specific instant in time with millisecond precision. java.util.Calendar is an abstract base class for extracting detailed information such as year, month, date, hour, minute and second from a Date object. Subclasses of Calendar can implement specific calendar systems such as Gregorian calendar, Lunar Calendar and Jewish calendar. Currently, java.util.GregorianCalendar for the Gregorian calendar is supported in the Java API. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 114 The GregorianCalendar Class You can use new GregorianCalendar() to construct a default GregorianCalendar with the current time and use new GregorianCalendar(year, month, date) to construct a GregorianCalendar with the specified year, month, and date. The month parameter is 0- based, i.e., 0 is for January. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 115 The get Method in Calendar Class The get(int field) method defined in the Calendar class is useful to extract the value for a given time field. The time fields are defined as constants such as YEAR, MONTH, DATE, HOUR (for the 12-hour clock), HOUR_OF_DAY (for the 24-hour clock), MINUTE, SECOND, DAY_OF_WEEK (the day number within the current week with 1 for Sunday), DAY_OF_MONTH (same as the DATE value), DAY_OF_YEAR (the day number within the current year with 1 for the first day of the year), WEEK_OF_MONTH (the week number within the current month), and WEEK_OF_YEAR (the week number within the current year). For example, the following code Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 116 Interfaces An interface is a classlike construct that contains only constants and abstract methods. In many ways, an interface is similar to an abstract class, but an abstract class can contain variables and concrete methods as well as constants and abstract methods. To distinguish an interface from a class, Java uses the following syntax to declare an interface: public interface InterfaceName { constant declarations; method signatures; } Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 117 Interface is a Special Class An interface is treated like a special class in Java. Each interface is compiled into a separate bytecode file, just like a regular class. Like an abstract class, you cannot create an instance from an interface using the new operator, but in most cases you can use an interface more or less the same way you use an abstract class. For example, you can use an interface as a data type for a variable, as the result of casting, and so on. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 118 Define Interfaces Suppose you want to design a generic method to find the larger of two objects. The objects can be students, dates, or circles. Since compare methods are different for different types of objects, you need to define a generic compare method to determine the order of the two objects. Then you can tailor the method to compare students, dates, or circles. For example, you can use student ID as the key for comparing students, radius as the key for comparing circles, and volume as the key for comparing dates. You can use an interface to define a generic compareTo method, as follows: Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 119 Example of an Interface // This interface is defined in // java.lang package package java.lang; public interface Comparable { public int compareTo(Object o); } Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 120 String and Date Classes Many classes (e.g., String and Date) in the Java library implement Comparable to define a natural order for the objects. If you examine the source code of these classes, you will see the keyword implements used in the classes, as shown below: public class String extends Object implements Comparable { // class body omitted } public class Date extends Object implements Comparable { // class body omitted } new String() instanceof String new String() instanceof Comparable new java.util.Date() instanceof java.util.Date new java.util.Date() instanceof Comparable Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 121 Generic max Method // Max.java: Find a maximum object public class Max { /** Return the maximum of two objects */ public static Object max (Object o1, Object o2) { if (((Comparable)o1).compareTo(o2) > 0) return o1; else return o2; } } (a) // Max.java: Find a maximum object public class Max { /** Return the maximum of two objects */ public static Comparable max (Comparable o1, Comparable o2) { if (o1.compareTo(o2) > 0) return o1; else return o2; } } (b) String s1 = "abcdef"; String s2 = "abcdee"; String s3 = (String)Max.max(s1, s2); Date d1 = new Date(); Date d2 = new Date(); Date d3 = (Date)Max.max(d1, d2); The return value from the max method is of the Comparable type. So, you need to cast it to String or Date explicitly. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 122 Declaring Classes to Implement Comparable You cannot use the max method to find the larger of two instances of Rectangle, because Rectangle does not implement Comparable. However, you can declare a new rectangle class that implements Comparable. The instances of this new class are comparable. Let this new class be named ComparableRectangle. ComparableRectangle ComparableRectangle rectangle1 = new ComparableRectangle(4, 5); ComparableRectangle rectangle2 = new ComparableRectangle(3, 6); System.out.println(Max.max(rectangle1, rectangle2)); Rectangle - GeometricObject - «interface» java.lang.Comparable +compareTo(o: Object): int Notation: The interface name and the method names are italicized. The dashed lines and hollow triangles are used to point to the interface. ComparableRectangle - Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 123 Interfaces vs. Abstract Classes In an interface, the data must be constants; an abstract class can have all types of data. Each method in an interface has only a signature without implementation; an abstract class can have concrete methods. Variables Constructors Methods Abstract class No restrictions Constructors are invoked by subclasses through constructor chaining. An abstract class cannot be instantiated using the new operator. No restrictions. Interface All variables must be public static final No constructors. An interface cannot be instantiated using the new operator. All methods must be public abstract instance methods Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 124 Interfaces vs. Abstract Classes, cont. All data fields are public final static and all methods are public abstract in an interface. For this reason, these modifiers can be omitted, as shown below: public interface T1 { public static final int K = 1; public abstract void p(); } Equivalent public interface T1 { int K = 1; void p(); } A constant defined in an interface can be accessed using syntax InterfaceName.CONSTANT_NAME (e.g., T1.K). Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 125 Interfaces vs. Abstract Classes, cont. Object Class1 Interface1 Interface1_1 Interface1_2 Class2 Interface2_1 Interface2_2 Suppose that c is an instance of Class2. c is also an instance of Object, Class1, Interface1, Interface1_1, Interface1_2, Interface2_1, and Interface2_2. All classes share a single root, the Object class, but there is no single root for interfaces. Like a class, an interface also defines a type. A variable of an interface type can reference any instance of the class that implements the interface. If a class extends an interface, this interface plays the same role as a superclass. You can use an interface as a data type and cast a variable of an interface type to its subclass, and vice versa. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 126 Caution: conflict interfaces In rare occasions, a class may implement two interfaces with conflict information (e.g., two same constants with different values or two methods with same signature but different return type). This type of errors will be detected by the compiler. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 127 Whether to use an interface or a class? Abstract classes and interfaces can both be used to model common features. How do you decide whether to use an interface or a class? In general, a strong is-a relationship that clearly describes a parent- child relationship should be modeled using classes. For example, a staff member is a person. So their relationship should be modeled using class inheritance. A weak is-a relationship, also known as an is-kind-of relationship, indicates that an object possesses a certain property. A weak is-a relationship can be modeled using interfaces. For example, all strings are comparable, so the String class implements the Comparable interface. You can also use interfaces to circumvent single inheritance restriction if multiple inheritance is desired. In the case of multiple inheritance, you have to design one as a superclass, and others as interface. See Chapter 10, “Object- Oriented Modeling,” for more discussions. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 128 Creating Custom Interfaces public interface Edible { /** Describe how to eat */ public String howToEat(); } class Animal { } class Chicken extends Animal implements Edible { public String howToEat() { return "Fry it"; } } class Tiger extends Animal { } class abstract Fruit implements Edible { } class Apple extends Fruit { public String howToEat() { return "Make apple cider"; } } class Orange extends Fruit { public String howToEat() { return "Make orange juice"; } } Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 129 class Chicken extends Animal implements Edible, Comparable { int weight; public Chicken(int weight) { this.weight = weight; } public String howToEat() { return "Fry it"; } public int compareTo(Object o) { return weight – ((Chicken)o).weight; } } Implements Multiple Interfaces Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 130 Creating Custom Interfaces, cont. public interface Edible { /** Describe how to eat */ public String howToEat(); } public class TestEdible { public static void main(String[] args) { Object[] objects = {new Tiger(), new Chicken(), new Apple()}; for (int i = 0; i < objects.length; i++) showObject(objects[i]); } public static void showObject(Object object) { if (object instanceof Edible) System.out.println(((Edible)object).howToEat()); } } Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 131 The Cloneable Interfaces package java.lang; public interface Cloneable { } Marker Interface: An empty interface. A marker interface does not contain constants or methods. It is used to denote that a class possesses certain desirable properties. A class that implements the Cloneable interface is marked cloneable, and its objects can be cloned using the clone() method defined in the Object class. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 132 Examples Many classes (e.g., Date and Calendar) in the Java library implement Cloneable. Thus, the instances of these classes can be cloned. For example, the following code Calendar calendar = new GregorianCalendar(2003, 2, 1); Calendar calendarCopy = (Calendar)calendar.clone(); System.out.println("calendar == calendarCopy is " + (calendar == calendarCopy)); System.out.println("calendar.equals(calendarCopy) is " + calendar.equals(calendarCopy)); displays calendar == calendarCopy is false calendar.equals(calendarCopy) is true Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 133 Implementing Cloneable Interface To declare a custom class that implements the Cloneable interface, the class must override the clone() method in the Object class. The following code declares a class named House that implements Cloneable and Comparable. House Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 134 Shallow vs. Deep Copy house1: House id = 1 area = 1750.50 whenBuilt 1 Memory whenBuilt: Date date object contents house2 = house1.clone() 1750.50 reference house1: House id = 1 area = 1750.50 whenBuilt 1 Memory 1750.50 reference House house1 = new House(1, 1750.50); House house2 = (House)house1.clone(); Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 135 Wrapper Classes  Boolean  Character  Short  Byte  Integer  Long  Float  Double Object - Double - Float - Long - Integer - Short - Byte - Character - Boolean - Number - Comparable - NOTE: (1) The wrapper classes do not have no-arg constructors. (2) The instances of all wrapper classes are immutable, i.e., their internal values cannot be changed once the objects are created. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 Object-Oriented Design 136 Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 137 Software Development Process Requirement Specification System Analysis System Design Testing Implementation Maintenance Deployment Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 138 Requirement Specification Requirement Specification System Analysis System Design Testing Implementation Maintenance Deployment A formal process that seeks to understand the problem and document in detail what the software system needs to do. This phase involves close interaction between users and designers. Most of the examples in this book are simple, and their requirements are clearly stated. In the real world, however, problems are not well defined. You need to study a problem carefully to identify its requirements. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 139 System Analysis Requirement Specification System Analysis System Design Testing Implementation Maintenance Deployment Seeks to analyze the business process in terms of data flow, and to identify the system’s input and output. Part of the analysis entails modeling the system’s behavior. The model is intended to capture the essential elements of the system and to define services to the system. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 140 System Design Requirement Specification System Analysis System Design Testing Implementation Maintenance Deployment The process of designing the system’s components. This phase involves the use of many levels of abstraction to decompose the problem into manageable components, identify classes and interfaces, and establish relationships among the classes and interfaces. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 141 Implementation Requirement Specification System Analysis System Design Testing Implementation Maintenance Deployment The process of translating the system design into programs. Separate programs are written for each component and put to work together. This phase requires the use of a programming language like Java. The implementation involves coding, testing, and debugging. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 142 Testing Requirement Specification System Analysis System Design Testing Implementation Maintenance Deployment Ensures that the code meets the requirements specification and weeds out bugs. An independent team of software engineers not involved in the design and implementation of the project usually conducts such testing. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 143 Deployment Requirement Specification System Analysis System Design Testing Implementation Maintenance Deployment Deployment makes the project available for use. For a Java applet, this means installing it on a Web server; for a Java application, installing it on the client's computer. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 144 Maintenance Requirement Specification System Analysis System Design Testing Implementation Maintenance Deployment Maintenance is concerned with changing and improving the product. A software product must continue to perform and improve in a changing environment. This requires periodic upgrades of the product to fix newly discovered bugs and incorporate changes. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 145 Relationships among Classes Association Aggregation Composition Inheritance Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 146 Association Association represents a general binary relationship that describes an activity between two classes. Student * 5..60 Take Teach 0..3 1 Teacher Faculty Course public class Student { /** Data fields */ private Course[] courseList; /** Constructors */ /** Methods */ } public class Course { /** Data fields */ private Student[] classList; private Faculty faculty; /** Constructors */ /** Methods */ } public class Faculty { /** Data fields */ private Course[] courseList; /** Constructors */ /** Methods */ } An association is usually represented as a data field in the class. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 147 Association Between Same Class Association may exist between objects of the same class. For example, a person may have a supervisor. Person Supervisor 1 1 Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 148 Aggregation and Composition Aggregation is a special form of association, which represents an ownership relationship between two classes. Aggregation models the has-a relationship. If an object is exclusively owned by an aggregated object, the relationship between the object and its aggregated object is referred to as composition. Name Address Person Composition Aggregation Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 149 Representing Aggregation in Classes An aggregation relationship is usually represented as a data field in the aggregated class. public class Name { /** Data fields */ /** Constructors */ /** Methods */ } public class Person { /** Data fields */ private Name name; private Address address; /** Constructors */ /** Methods */ } public class Address { /** Data fields */ /** Constructors */ /** Methods */ } Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 150 Inner Classes Translation If Name or Address is used in the Person class only, they can be declared as an inner class in Person. For example, public class Person { private Name name; private Address address; ... class Name { ... } class Address { ... } } Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 151 Inheritance Inheritance models the is-an-extension-of relationship between two classes. Person Faculty public class Faculty extends Person { /** Data fields */ /** Constructors */ /** Methods */ } (A) (B) Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 152 Weak Inheritance Relationship A weak is-an-extension-of relationship can be represented using interfaces. For example, the weak is-an-extension-of relationship “students are comparable based on their grades” can be represented by implementing the Comparable interface, as follows: Person Student Comparable public class Student extends Person implements Comparable { /** Data fields, Constructors, and */ /** Methods */ /** Implement the compareTo method */ public int compareTo(Object object) { // ... } } (A) (B) Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 153 Class Design 1. Identify classes for the system. 2. Describe attributes and methods in each class. 3. Establish relationships among classes. 4. Create classes. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 154 Example 11.1 Borrowing Loans Name Borrower Person Loan Address Loan Borrower -loan: Loan +Borrower() +Borrower(name: Name, address: Address) +getLoan(): Loan +setLoan(loan: Loan): void +toString(): String Address -street: String -city: String -state: String -zip: String +Address() +Address(street: String, city: String, state: String, zip: String) +getStreet(): String +getCity(): String +getState(): String +getZip(): String +setStreet(street: String): void +setCity(city: String): void +setState(state: String): void +setZip(zip: String): void +getFullAddress(): String Defined in Example 6.7 Person -name: Name -address: Address +Person() +Person(name: Name, address: Address) +getName(): Name +seName(name: Name): void +getAddress(): Address +setAddress(address: Address): void +toString(): String Name -firstName: String -mi: char -lastName: String +Name() +Name(firstName: String, mi: char, lastName: String) +getFirstName(): String +getMi(): char +getLastName(): String +setFirstName(firstName: String): void +setMi(mi: char): void +setLastName(lastName: String): void +getFullName(): String Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 155 Example 11.1 Borrowing Loans, cont. The following is a test program that uses the classes Name, Person, Address, Borrower, and Loan. BorrowLoan Run Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 156 Example 11.2 The Rational Class Rational Run TestRationalClass 1 1 Add, Subtract, Multiply, Divide Rational -numerator: long -denominator: long +Rational() +Rational(numerator: long, denominator: long) +getNumerator(): long +getDenominator(): long +add(secondRational: Rational): Rational +multiply(secondRational: Rational): Rational +subtract(secondRational: Rational): Rational +divide(secondRational: Rational): Rational +toString(): String -gcd(n: long, d: long): long java.lang.Number +byteValue(): byte +shortValue(): short +intValue(): int +longVlaue(): long +floatValue(): float +doubleValue():double java.lang.Comparable compareTo(Object): int Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 157 Class Design Guidelines Designing a Single Class. Using Modifiers public, protected, private and static Using Inheritance or Aggregation Using Interfaces or Abstract Classes Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 158 Designing a Class A class should describe a single entity or a set of similar operations. A single entity with too many responsibilities can be broken into several classes to separate responsibilities. The String class, StringBuffer class, and StringTokenizer class all deal with strings, for example, but have different responsibilities. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 159 Designing a Class, cont. Classes are usually designed for use by many different customers. To make a class useful in a wide range of applications, the class should provide a variety of ways for customization through properties and methods. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 160 Designing a Class, cont. Classes are designed for reuse. Users can incorporate classes in many different combinations, orders, and environments. Therefore, you should design a class that imposes no restrictions on what or when the user can do with it, design the properties to ensure that the user can set properties in any order, with any combination of values, and design methods to function independently of their order of occurrence. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 161 Designing a Class, cont. Provide a public no-arg constructor and override the equals method and the toString method defined in the Object class whenever possible. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 162 Designing a Class, cont. Follow standard Java programming style and naming conventions. Choose informative names for classes, data fields, and methods. Always place the data declaration before the constructor, and place constructors before methods. Always provide a constructor and initialize variables to avoid programming errors. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 163 Using Visibility Modifiers  Each class can present two contracts – one for the users of the class and one for the extenders of the class. Make the fields private and accessor methods public if they are intended for the users of the class. Make the fields or method protected if they are intended for extenders of the class. The contract for the extenders encompasses the contract for the users. The extended class may increase the visibility of an instance method from protected to public, or change its implementation, but you should never change the implementation in a way that violates that contract. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 164 Using Visibility Modifiers, cont. A class should use the private modifier to hide its data from direct access by clients. You can use get methods and set methods to provide users with access to the private data, but only to private data you want the user to see or to modify. A class should also hide methods not intended for client use. The gcd method in the Rational class in Example 11.2, “The Rational Class,” is private, for example, because it is only for internal use within the class. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 165 Using the static Modifier A property that is shared by all the instances of the class should be declared as a static property. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 166 Using Inheritance or Aggregation In general, the difference between inheritance and aggregation is the difference between the is-an-extension-of relationship and the has-a relationship. For example, an apple is fruit; thus, you would use inheritance to model the relationship between the classes Apple and Fruit. A person has a name; thus, you would use aggregation to model the relationship between the classes Person and Name. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 167 Using Inheritance or Aggregation, cont. Sometimes, the choice between inheritance and aggregation is not obvious. For example, you have used inheritance to model the relationship between the classes Circle and Cylinder. One could argue that a cylinder consists of circles; thus, you might use aggregation to define the Cylinder class as follows: Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 168 Using Inheritance or Composition, cont. public class Cylinder { private Circle circle; /** Constructors */ /** Methods */ } Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 169 Using Inheritance or Aggregation, cont. Both designs are fine. Which one is preferred? If polymorphism is desirable, you need to use the inheritance design. If you don’t care about polymorphism, the aggregation design gives more flexibility because the classes are less dependent using aggregation than using inheritance. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 170 Using Interfaces or Abstract Classes Both interfaces and abstract classes can be used to generalize common features. How do you decide whether to use an interface or a class? In general, a strong is-an-extension-of relationship that clearly describes a parent- child relationship should be modeled using classes. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 171 Using Interfaces or Abstract Classes, cont. For example, since an orange is a fruit, their relationship should be modeled using class inheritance. A weak is-an- extension-of relationship, also known as an is-kind-of relationship, indicates that an object possesses a certain property. A weak is-an-extension-of relationship can be modeled using interfaces. For example, all strings are comparable, so the String class implements the Comparable interface. A circle or a rectangle is a geometric object, for example, so Circle can be designed as a subclass of GeometricObject. Circles are different and comparable based on their radius, for example, so Circle can implement the Comparable interface. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 172 Using Interfaces or Abstract Classes, cont. Interfaces are more flexible than abstract classes, because a subclass can extend only one superclass, but implement any number of interfaces. However, interfaces cannot contain concrete methods. You can combine the virtues of interfaces and abstract classes by creating an interface with a companion abstract class that implements the interface. So you can use the interface or its companion class whichever is more convenient. Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 173 Sequence diagrams Sequence diagrams describe interactions among objects by depicting the time ordering of method invocations. anObject: TheClass Class role Method Invocation Activation anotherObject: TheOtherClass Method Invocation anotherMethod() aMethod() Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 174 Sequence diagrams, cont. name: Name : BorrowLoan address: Address loan: Loan borrower: Borrower setFirstName setMi setLastName setStreet setCity setState setZip setAnnualInterestRate setNumOfYears setLoanAmount setName setAddress setLoan Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 175 Statechart diagrams Statechart diagrams describe flow of control of the object. Indicate Initial State Transition State1 State2 Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 176 Statechart diagrams, cont. Class Loaded JVM loads the class for the object Use the new operator to create the object Object Created Invoke the finalize method on the object Object Destroyed Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 177 Supplement P: Designing Generic Matrix Classes  Objective: This example gives a generic class for matrix arithmetic. This class implements matrix addition and multiplication common for all types of matrices. GenericMatrix Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 178 Example 11.3, cont. GenericMatrix -matrix: Object[][] #GenericMatrix(matrix: Object[][]) +getMatrix(): Object[][] +setMatrix(matrix: Object[][]): void +addMatrix(secondMatrix: Object[][]): Object[][] +multiplyMatrix(secondMatrix: Object[][]): Object[][] +printResult(m1: GenericMatrix, m2: GenericMatrix, m3: GenericMatrix, op: char): void #createGenericMatrix():GenericMatrix #add(o1: Object, o2: Object): Object #multiply(o1: Object, o2: Object): Object #zero():Object IntegerMatrix RationalMatrix Liang, Introduction to Java Programming, Sixth Edition, (c) 2005 Pearson Education, Inc. All rights reserved. 0-13-148952-6 179 Example 11.3, cont.  Objective: This example gives two programs that utilize the GenericMatrix class for integer matrix arithmetic and rational matrix arithmetic. TestIntegerMatrix Run TestRationalMatrix Run RationalMatrix IntegerMatrix