javabeans-guide's Introduction

JavaBeans Creation Guide

Creation of a simple JavaBean component. The purpose of this repository is educational.

Steps to follow

Create EventBeanValue class that inherits from EventObject.

This class will store the old and new values of the JavaBean.

public class EventBeanValue extends EventObject {
	private int oldValue, newValue;
}

Create BeanValueListener interface that extends from EventListener.

This interface must have a method forcing implementing classes to fill it with their response to the event.

public interface BeanValueListener extends EventListener {
	/**
	 * Method to be run when the event occurs
	 * @param ev Object that describes the change that has been made.
	 */
	public void awareOfChangeInValue(EventBeanValue ev);
}

Create Bean class

This class must follow this points:

Implement Serializable. This allows instances of this class to be saved at any time.
Implement default (empty) constructor and have get, set and is methods.
Have a List of BeanValueListeners. This list must have methods declared with synchronized modifier to add and remove a certain listener.
A setValue() method that does the following when a new value is set:
- Create an EventBeanValue describing the change
- Create a copy of the listeners' list in a synchronized block
- Notify each element of the copy using the method they inherit from BeanValueListener

// Notifies the change event to all subscribers
EventBeanValue ev = new EventBeanValue(this, oldValue, newValue);
notifyChange(ev);

/**
 * Firstly, creates a copy of the list in order to prevent concurrency problems.
 * After that, notifies the value change to all subscribers
 */
private void notifyChange(EventBeanValue ev) {
	List<BeanValueListener> copy;
	synchronized (this) {
		copy = new ArrayList<>(listeners);
	}

	for (BeanValueListener listener : copy) {
		listener.awareOfChangeInValue(ev);
	}
}

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