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101

Figure 6-1– The Person class, showing private, protected, and public variables, and

static and abstract methods

The top part of the box contains the class name and package name (if any).

The second compartment lists the class’s variables, and the bottom

compartment lists its methods. The symbols in front of the names indicate

that member’s visibility, where “+” means public, “- ” means private, and

“#” means protected. Static methods are shown underlined. Abstract

methods may be shown in italics or, as shown in Figure Figure 6-1, with

an “{abstract}” label.

You can also show all of the type information in a UML diagram where

that is helpful, as illustrated in Figure 6-2a.

Figure 6-2 - The Person class UML diagram shown both with and without the

method types

UML does not require that you show all of the attributes of a class, and it

is usual only to show the ones of interest to the discussion at hand. For

example, in Figure 6-2 b, we have omitted some of the method details.

102

Inheritance

Let’s consider a version of Person that has public, protected, and private

variables and methods, and an Emplo yee class derived from it. We will

also make the getJob method abstract in the base Person class, which

means we indicate it with the MustOverride keyword.

public abstract class Person {

protected string name;

private int age;

//-----

public Person( string nm, int ag) {

name = nm;

age = ag;

}

public string makeJob() {

return "hired";

}

public int getAge() {

return age;

}

public void splitNames() {

}

public abstract string getJob(); //must override

}

We now derive the Employee class from it, and fill in some code for the

getJob method.

public class Employee : Person {

public Employee( string nm, int ag): base (nm, ag){

}

public override string getJob() {

return "Worker";

}

You represent inheritance using a solid line and a hollow triangular arrow.

For the simple Employee class that is a subclass of Person, we represent

this in UML, as shown in Figure 6-3

103

Figure 6-3 – The UML diagram showing Employee derived from Person

Note that the name of the Employee class is not in italics because it is now

a concrete class and because it includes a concrete method for the formerly

abstract getJob method. While it has been conventional to show the

inheritance with the arrow pointing up to the superclass, UML does not

require this, and sometimes a different layout is clearer or uses space more

efficiently.

Interfaces

An interface looks much like inheritance, except that the arrow has a

dotted line tail, as shown in Figure 6-4. The name <<interface>> may

also be shown, enclosed in double angle brackets, or guillamets.

Figure 6-4 – ExitCommand implements the Command interface.

Composition

Much of the time, a useful representation of a class hierarchy must include

how objects are contained in other objects. For example, a small company

might include one Employee and one Person (perhaps a contractor).

104

public class Company {

private Employee emp;

private Person prs;

public Company() {

}

We represent this in UML, as shown in Figure 6-5.

Figure 6-5 – Company contains instances of Person and Employee.

The lines between classes show that there can be 0 to 1 instances of Person

in Company and 0 to 1 instances of Employee in Company. The diamonds

indicate the aggregation of classes within Company.

If there can be many instances of a class inside another, such as the array

of Employees shown here

public class Company {

private Employee[] emps;

private Empoyee emp;

private Person prs;

public Company() {

}

we represent that object composition as a single line with either a “*” on it

or “0, *” on it, as shown in Figure 6-6.

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Figure 6-6 – Company contains any number of instances of Employee.

Some writers have used hollow and solid diamond arrowheads to indicate

containment of aggregates and circle arrowhead for single object

composition, but this is not required.

Annotation

You will also find it convenient to annotate your UML or insert comments

to explain which class calls a method in which other class. You can place

a comment anywhere you want in a UML diagram. Comments may be

enclosed in a box with a turned corner or just entered as text. Text

comments are usually shown along an arrow line, indicating the nature of

the method that is called, as shown in Figure 6-7.

(Ebook) C Sharp - Introduction To Design Pattern In C Sharp Vol_2 - Ibm.pdf

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