Programming Tutorials

Design Patterns for Properties in a Java Bean

By: Sam Chen in Java Beans Tutorials on 2007-09-15  

Properties in Java Beans are usually implemented using a combination of private instance variables and public accessor/mutator methods (getters/setters). However, there are several design patterns that can be used to implement properties in Java Beans in a more efficient and maintainable manner. Here are a few design patterns for properties in Java Beans:

1. Simple Property Pattern: This pattern involves creating a private instance variable for each property and providing a public getter and setter method for each variable. This pattern is simple and straightforward, but can become tedious if there are a large number of properties to manage.

2. Indexed Property Pattern: This pattern is used when you need to manage a collection of related properties. For example, if you have a Java Bean that represents a database record, you might want to provide access to the individual fields in the record using an index. In this pattern, you create a private array to hold the property values and provide getter and setter methods that take an index parameter.

3. Bound Property Pattern: This pattern is used when you want to notify other objects when a property changes. In this pattern, you define a property change listener interface and add methods to your bean to register and unregister listeners. When a property changes, you fire a property change event that notifies all registered listeners.

4. Constrained Property Pattern: This pattern is similar to the bound property pattern, but is used when you want to validate the new value of a property before allowing it to be set. In this pattern, you define a property change listener interface that includes a method for validating the new value. When a property changes, you fire a property change event that notifies all registered listeners. Before allowing the new value to be set, you validate it by calling the validation method of all registered listeners.

Here is an example implementation of the Simple Property Pattern in a Java Bean:

public class Person {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

This Java Bean has two properties, "name" and "age", each with a private instance variable and a public getter and setter method. This implementation is simple and easy to understand, but can become tedious if there are many properties to manage. Other design patterns, such as the Indexed Property Pattern or the Bound Property Pattern, can be used to manage large collections of properties or to notify other objects when a property changes.