11.16 A JAVA STUDY OF INTERLEAVED CLASSES OF MODERATE COMPLEXITY

Class interleaving is not an issue with Java because of the look-ahead capability of the Java compiler. Each Java class is self-contained and Java classes can appear in any order in a file. Although the recommended approach to code organization is for a file to contain a single class, it is not uncommon to bundle a large class with some related but small ancillary classes in the same file.

The purpose of this section is simply to draw a comparison with the code shown in the previous section and to point out the programming ease made possible by the absence of issues related to class interleaving, pointers, memory allocation and deallocation, and so on. It will not be necessary now to have copy constructors and copy assignment operators, although you may have to provide override definitions for clone so that duplicates of objects can be constructed. Also, since garbage collection in Java automatically deallocates the memory occupied by an object if there are no variables holding references to the object, you will also not need destructors any more. Here is the code:

 
 //Interleaved.java import java.util.*; //////////////////////////// class Date  //////////////////////////// class Date implements Cloneable {     int month;     int day;     int year;     public Date( int mm, int dd, int yy ) {         month = mm; day = dd; year = yy;     }     public String toString() {         return month + " : " + day + " : " + year;     }     public Object clone()     {         Date date = null;         try {             date = ( Date ) super. clone ();         } catch( CloneNotSupportedException e ) {}         return date;     } } ///////////////////////////// class Cat ///////////////////////////// class Cat implements Cloneable {     String name;     int age;     public Cat( String nam, int a ) { name = nam; age = a; }     public String toString() { return " Name: " + name                                        + "  Age: " + age; }          public Object clone() {         Cat cat = null;         try {             cat = ( Cat ) super.clone();         } catch( ClcneNotSupportedException e ) {}         return cat;     } } ///////////////////////////// class Dog //////////////////////////// class Dog implements Cloneable {     String name;     int age;     public Dog( String nam, int a ) { name = nam; age = a; }     public String toString() { return "\nName: " + name                                       + " Age: " + age; }     public String getName() { return name; }     public int getAge() { return age; }          public void print() {         System.out.println( this );     }     public Object clone() throws CloneNotSupportedException {         Dog dog = null;         try {             dog = ( Dog ) super.clone();         } catch( CloneNotSupportedException e ) {}         return dog;     } }   ////////////////////////// class Employee ////////////////////////// class Employee {                    // intentionally left uncloneable           String firstName, lastName;     Date dateOfBirth;     Employee [] friends;     Auto[] autos;     Cat kitty;     Vector dogs;     Map phoneList;     public Employee( String first, String last ) {         firstName = first; lastName = last;     }     public Employee( String first, String last, Date dob ) {         firstName = first; lastName = last;         dateOfBirth = dob == null ? null : (Date) dob.clone();     }     public Employee ( String first, String last, Date dob, Cat kit ) {         firstName = first; lastName = last;         dateOfBirth = dob == null ? null : (Date) dob.clone();         kitty = kit == null ? null : (Cat) kit. clone();     }     public Employee( String first, String last, Vector dogs ) {         firstName = first; lastName = last;         this.dogs = dogs == null ? null : (Vector) dogs.clone();     }     Employee( String first, String last, Date dob, Employee[] fnds ) {         firstName = first; lastName = last;         dateOfBirth = dob == null ? null : (Date) dob.clone();         friends = fnds == null ? null : (Employee[] fnds.clone();     }     Employee( String first, String last, Map phoneList ) {         firstName = first; lastName = last;         this.phoneList = phoneList == null ? nul           : new TreeMap( (TreeMap) phoneList );     }     Employee( String first, String last, Date dob, Employee[] fnds,                    Auto[] ats, Cat c )     {         firstName = first; lastName = last;         dateOfBirth = dob == null ? null : (Date) dob.clone();         friends = fnds == null ? null : (Employee[]) fnds.clone();         autos = ats == null ? null : (Auto[]) ats.clone();         kitty = c == null ? null : (Cat) c.clone();     }     String getFirstName() { return firstName; }     String getLastName() { return lastName; }     public String toString() {         String str = "";         if ( dogs != null ) {             str += "\nDOGS: ";             for ( int i=0; i<dogs.size(); i++ ) {                 str += (Dog) dogs.elementAt(i);             }             str += "\n";         }         if ( autos != null ) {             str += "\nAUTOS: ";             for ( int i=0; i<autos.length - 1; i++ ) {                 str += " " + autos[i] + ",";             }             str += " " + autos[autos.length - 1];             str += "\n";         }         if ( friends != null ) {             str += "\nFRIENDS:";             for ( int i=0; i<friends.length; i++ ) {                 str += "\n";                 str += friends[i] .getFirstName();                 str += " " + friends[i] .getLastName();             }             str += "\n"***         }         if ( kitty != null ) {             str += "\nCAT:";             str += kitty;         }         if ( phoneList != null ) {             str += "\nPhone List:";             str += phoneList;         }         return "\nFirst Name: " + firstName                     + "\nLast Name: " + lastName                     + "\n" + str + "\n"     } } //////////////////////////// class Auto ///////////////////////////// class Auto {     String autoBrand;     Employee owner;     public Auto( String brand ) { autoBrand = brand; }     public Auto( String brand, Employee e )     {         autoBrand = brand;         owner = e;     }     public String toString()     {         return autoBrand;     } }   //////////////////////// class TestEmployee //////////////////////// class TestEmployee {     public static void main( String[] args )     {         Employee e1 = new Employee( "Zoe", "Zaphod" );         Employee e2 = new Employee( "YoYo", "Ma",                                  new Date( 2, 12, 2000 ) );         Employee[] empList = new Employee[2];         empList[0] = e1;         empList[1] = e2;           Auto[] autoList = new Auto[2];         Auto a1 = new Auto( "Chevrolet" );         Auto a2 = new Auto( "Ford" );         autoList[0] = a1;         autoList[1] = a2;         Cat purr = new Cat( "socks", 5 );         System.out.println( "TEST 1: " );         Employee e3 = new Employee( "Bebe", "Ruth",                        new Dated(1, 2, 2000),                        empList, autoList, purr );         System.out.println( e3 );                   Employee e4;         e4 = e3;         System.out.println( e4 );                   System.out.println( "\n\nTEST 2: " );                    // what if the kitty reference is null ?         Employee e5 = new Employee( "Bebe", "Ruth",                          new Date(1, 2, 2000),                          empList, autoList, null );         System.out.println( e5 );                  System.out.println( "\n\nTEST 3: " );           // what if autoList reference is null also ?         Employee e6 = new Employee( "Bebe", "Ruth",                          new Date(1, 2, 2000),                          empList, null, null );         System.out.println( e6 );                  System.out.println( "\n\nTEST 4: " );         // what if empList reference for friends is null also ?         Employee e7 = new Employee( "Bebe", "Ruth",                          new Date(1, 2, 2000),                          null, null, null );         System.out.println( e7 );                  Employee e8 = e7;         System.out.println( "\n\nTEST 5: " );         // try the vector data member         Dog dog1 = new Dog( "fido", 3 );         Dog dog2 = new Dog( "spot", 4 );         Vector dawgs = new Vector();         dawgs.addElement( dog1 );         dawgs.addElement( dog2 );         Employee e9 = new Employee( "Linda", "Ellerbee", dawgs );         System.out.println( e9 );                  System.out.println( "\n\nTEST 6: " ) ;         // try the map<string, int> data member         Map phList = new TreeMap();         phList.put( "Steve Martin", new Integer( 1234567 ) );         phList.put( "Bill Gates", new Integer( 100100100 ) );                    Employee e10 = new Employee( "Will", "Rogers", phList );         System.out.println( e10 );     } }

The output of this program is as follows:

 
 TEST 1: First Name: Bebe Last Name: Ruth AUTOS: Chevrolet, Ford FRIENDS: Zoe Zaphod YoYo Ma CAT: Name: socks  Age: 5 TEST 2: First Name: Bebe Last Name: Ruth AUTOS: Chevrolet, Ford FRIENDS: Zoe Zaphod YoYo Ma TEST 3: First Name: Bebe Last Name: Ruth FRIENDS: Zoe Zaphod YoYo Ma TEST 4: First Name: Bebe Last Name: Ruth TEST 5: First Name: Linda Last Name: Ellerbee DOGS: Name: fido Age: 3 Name: spot Age: 4 TEST 6: First Name: Will Last Name: Rogers Phone List: {Bill Gates=100100100, Steve Martin=1234567}