ssrs 2d barcode Figure 1.6 Class associations in Java

Paint ECC200 in Java Figure 1.6 Class associations

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public String getName() { return new String(name); } }

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public class Professor extends Person { public static enum Rank {INSTR, ASST, ASSOC, PROF} private Rank rank; public Professor(String name, Rank rank) { super(name); this.rank = rank; } public Rank getRank() { return rank; } public void setRank(Rank rank) { this.rank = rank; } }

The Professor class extends the Person class, inheriting its name field and its getName method. It defines at line 2 an enum field named Rank that specifies the four values INSTR, ASST, ASSOC, and PROF. Its constructor at line 6 requires the professor s name and rank. Note how the Professor constructor uses the super keyword to invoke the Person constructor at line 7.

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public class University { private static class Department { final String name; Set<Professor> members; public Department(String name) { this.name = new String(name); this.members = new HashSet<Professor>(); } public void add(Professor professor) { members.add(professor); } } private final String name; private Map<String, Department> departments; public University(String name) { this.name = new String(name); this.departments = new TreeMap<String, Department>(); } public String getName() { return new String(name); }

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public void addDepartment(String name, Set<Professor> members) { Department dept = new Department(name); departments.put(name, dept); for (Professor prof : members) { dept.add(prof); } } public void add(Professor prof, String deptName) { Department dept = departments.get(deptName); if (dept == null) { throw new RuntimeException(deptName + " does not exist."); } else { dept.add(prof); } } public Set<String> departments() { return departments.keySet(); } }

The University class is a composite of Department objects. The existence of a department is dependent upon the existence of its university. Therefore, the Department class should be completely controlled and insulated by the University class. This is done by defining it to be a nested private static class at line 2. The University.Department class has two fields: name (a String), and members (a Set of Professors). It includes an add() method at line 11 for adding professors to the department. The University class has two fields: name (a String), and departments (a Map of Department objects, indexed by their names). It includes two add() methods (at lines 28 and 36) and an accessor method that returns the Set of department names (at line 45). Note that the University.Department class is an aggregate of Professor objects. The existence of a professor is independent of his or her department s existence. Therefore, the Professor class is defined separately from the University.Department class.

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public class TestUniversity { public static void main(String[] args) { University jsu = new University("JavaStateUniversity"); Professor adams = new Professor("Adams", Professor.Rank.ASSOC); Professor baker = new Professor("Baker", Professor.Rank.ASST); Professor cohen = new Professor("Cohen", Professor.Rank.PROF); Set<Professor> profs = new HashSet<Professor>(); Collections.addAll(profs, adams, baker, cohen); jsu.addDepartment("Computer Science", profs); Professor davis = new Professor("Davis", Professor.Rank.ASST); Professor evans = new Professor("Evans", Professor.Rank.INSTR); profs.clear(); Collections.addAll(profs, davis, evans, baker); jsu.addDepartment("Biology", profs); adams.setRank(Professor.Rank.PROF); } }

This test program creates the university with two departments, each containing three professors. Note that Prof. Baker is a member of both departments.

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The departments aggregation of professors is evidenced by two features of this program: A professor may belong to more than one department, and a professor s attributes may be changed independently of his or her department: Prof. Adams is promoted to Professor.Rank.PROF at line 15.

Example 1.6 uses several classes that are defined in the Java Collections Framework (JCF). This library is part of the java.util package. The JCF is outlined in 4. Example 1.6 also uses two new Java features, introduced with Java 5.0: enum types, and the for-each construct. THE UNIFIED MODELING LANGUAGE The Unified Modeling Language (UML) is illustrated in Figure 1.6 on page 10 and shows the symbols representing three kinds of association between classes. These are summarized in Table 1.6.