You need to draw a diagram of a simple bean that shows the relationships between different objects.

Use a simplified variant of a Unified Modeling Language (UML) class diagram that contains only class names, attribute names, and attribute types. Figure 3-1 describes two related beans—Person and Job.

Figure 3-1. Structure of Person and Job beans

Many of the recipes in this book deal with an object model consisting of JavaBeans, and, to save paper, I’ve devised this simple shorthand for describing a collection of related beans. Every time you see a diagram like Figure 3-1, mentally translate it to a set of classes, one for each box; each class attribute in that box is a private member variable, with a getter method and a setter method. The beans represented by these diagrams are simply objects with attributes, and the only operations on a bean are getter and setter methods and no-argument constructors. To help you get used to translating these diagrams into code, the Person and Job classes are defined in Examples Example 3-2 and Example 3-3.

public class Person {
    private String name;
    private Integer age;
    private Job job;

    public String getName( ) { return name; }
    public void setName(String name) { this.name = name; }

    public Integer getAge( ) { return age; }
    public void setAge(Integer age) { this.age = age; }

    public Job getJob( ) { return job; }
    public void setJob(Job job) { this.job = job; }
}

public class Job {
    private String title;
    private BigDecimal salary;

    public String getTitle( ) { return title; }
    public void setTitle(String title) { this.title = title; }

    public BigDecimal getSalary( ) { return salary; }
    public void setSalary(BigDecimal salary) { this.salary = salary; }
}

When an object contains an attribute of type List, it is helpful to know the type of object that List contains. To convey the type of object contained in a List, every list attribute will be followed by the type it is intended to contain surrounded by brackets: List<Integer>. Similarly, if an object contains a Map, the type of the key and value will be separated by a comma and surrounded by brackets: Map<String,Integer>. If the Person object had contained a list of Job objects instead of a single Job object, the attribute type would be written List<Job>, as in Figure 3-2.

Figure 3-2. Representing a list of Job objects

Don’t confuse UML with object-oriented design, as this is a mistake all too often made; UML captures the form and function of a system, but it is no substitute for a good design. All the drawings in the world won’t make a bad design good, and spending a day drawing a big UML diagram is simply a creative form of procrastination. That said, if you insist on drawing UML diagrams, check out some of the following tools: