CIS 270—Application Development II

1. CIS 270—Application Development II Chapter 8—Classes and Objects: A Deeper Look

2. 8.2.1 Time Class Case Study • Two classes: Time1 (Fig 8.1) and Time1Test (Fig. 8.2) • Time1 has three private instance variables and three public methods (a.k.a., public services or the public __________). • Time1 has a default ___________ that sets instance variables to 0. • Note the code hour = ((h>=0 && h<24) ? h:0); • It means if(h>=0 && h<24) hour=h; else hour=0; • The Time1 object will always have __________ data (always in range), but not necessarily correct data. interface constructor consistent

3. 8.2.2 Time Class Case Study • Note the code String.format(“%02d:%02d:%02d", hour, minute, second); in the Time1 class. • format is a method of the __________ class • The %02d means “format is leading 0, two decimal integers” (this formatted output is new in J2SE 5.0) • The three formats (in “”) will be applied to hour, minute, second • Likewise, note the code String.format( "%d:%02d:%02d %s", ( ( hour == 0 || hour == 12 ) ? 12 : hour % 12 ), minute, second, ( hour < 12 ? "AM" : "PM" ) ); • The hour % 12 means hour ______ 12 String mod

4. 8.2.3 Time Class Case Study • Note Time1 time = new Time1(); in the Time1Test class. • Variable time is assigned the address of a ________ object (time is a reference variable). • The code System.out.println( time.toUniversalString() ); prints the string returned when the object time calls the method toUniversalString() in the class _________. • The code time.setTime( 13, 27, 6 ); is the object time calling the setTime method in Time1. • The class MemberAccessTest in Fig. 8.3 shows that a client cannot directly access _________ members. Time1 Time1 private

5. 8.4 The this Reference • Note the file ThisTest.java in Fig. 8.4. • ThisTest.java has two classes (but only one can be public, which contains the ________ method here). • Compiling ThisTest.java will create two _______ files. • Parameter names for a constructor should NOT be the same as the instance variable (______) names. • Variables in a method with the same names as fields will shadow (hide) the fields. • In that case, you will need to refer to fields with the keyword _______. • Accessing members within the same class does not require the this reference (see Line 35). main .class field this

6. 8.5 Overloaded Constructors • Note class Time2 in Fig. 8.5. • A class can have several (__________) constructors if the ________ (parameter list) of each is different. • public Time2() is a no-__________ constructor. • this can be used as the first statement in a constructor’s body to call another constructor. • This use of this allows for code ______ with less maintenance if a constructor needs to be changed. • The methods setTime, toUniversalString, and toString use set and get methods instead of accessing instance variables directly. overloaded signature argument reuse

7. 8.6 Default and No-Argument Constructors • If a class has no constructors, the compiler creates a default constructor that sets numeric fields to 0, Boolean fields to false, and reference fields to ____. • If a class has constructors, the compiler will not create a default constructor. The class will need a no-argument constructor. • A no-argument constructor with no _____ will set fields to their default values. • A constructor is identified by Java because it has the same name as the class and has no _______ type. null body return

8. 8.7 Set and Get Methods • Classes provide public methods to allow clients to set and get ________ instance variables. • Set and get methods should only be used as needed. • Set methods are also called mutator methods and get methods are called _________ methods. • Set and get methods make private fields accessible, but not _______. • Get methods can hide the actual data format from the client when they return formatted data. • Set methods can protect fields from careless attempts to modify values by using ______ checking. private accessor public validity

9. 8.8 Composition • A data member of a class can be a reference to an ______ of another class. • This is known as composition or a _____ relationship. • Note that the Employee class in Fig. 8.8 uses composition. • Employeehas two Date objects as instance variables. • In UML (Unified _________ Language), composition would be expressed as follows: object has-a Modeling Employee Date

10. 8.9 Enumerations • An enumeration is a special kind of class which declares a set of _________. • enum types are final and __________. • Do not try to create an object of type enum. • An enum can have instance variables, constructors, and methods, much like an ordinary class. • Enhanced for loop (new in J2SE 5.0) • int scores[] = { 87, 93, 92, 95, 88, 90 }; • int var = 0; • for(int var : scores) // var holds each array value • totalScore += var; • See Fig. 8.10 and Fig. 8.11 for example of enum. constants static

11. 8.11 static Class Members • A static field (class variable) is shared by all objects. • Example: numOfItems in a class called Item: • public static int numberOfItems = 0; • In the constructor Item, include the code numberOfItems++; • A publicstatic field can be directly accessed by an object or with the _______ name: • anItem.numberOfItems • Item.numberOfItems • A ________ static field can be accessed by calling a publicstatic method using the class name: • Item.aMethod() • See Fig. 8.12 and Fig. 8.13 for examples. class private

12. 8.12-13 static Import and final Instance Variables • static Import • By using code like import static java.lang.Math.*; , you can access the static methods of a class without using the class name. • For example, sqrt(900.0) instead of ______.sqrt(900.0) • finalInstance Variables • Principle of _______ Privilege: code should be granted only the amount of privilege and access that it needs. • Instance variables can be made final—they can only be set in a constructor and cannot be changed otherwise. • private final int INCREMENT; Math Least

13. 8.14-15 Some OO Concepts • Software reuse • Java is a language, but it is also a ___________ for accessing the Java API (thousands of prewritten classes) • Software can be created by using prewritten components • Data abstraction and encapsulation • Information ______: classes hide their implementation from clients • Data abstraction: clients focus on data, not on implementation details • An __________ data type (ADT) has data representation and operations that manipulate the data • A class is an ADT—it has data and operations framework hiding abstract