JavaBeans

• Serializable
• Default constructor
• Getter and setter methods for accessing properties

• Often encapsulate multiple objects, allowing them to be passed around as a single object

import java.beans.*;

Features

• Introspection - query how a bean works
• Persistence - state, serializable
• Properties - attributes with consistent getters and setters
• Events - generating and handling events
• Customization - appearance and behavior can be altered

Default constructor

public class ClassName {
    public ClassName() {
    }
}

Simple properties

public class ClassName {
    private TYPE property;

    public TYPE getProperty() {
        return property;
    }
    public void setProperty(TYPE p) {
        property = p;
    }
}

• A boolean property can optionally have an isProperty() method, rather than a getProperty() method.

Indexed properties

public class ClassName {
    private TYPE[] property;

    public TYPE getProperty(int index) {
        return property[index];
    }
    public void setProperty(int index, TYPE p) {
        property[index] = p;
    }
    public TYPE[] getProperty() {
        return property;
    }
    public void setProperty(TYPE[] p) {
        property = new TYPE[p.length];
        System.arraycopy(p, 0, property, 0, p.length);
    }
}

Serializable

• Automatic: Implement Serializable

public class ClassName implements java.io.Serializable {
}

• Selective: Exclude fields you do not want serialized by marking with the transient (or static) modifier
• Custom: Define one or both of the following methods:

private void writeObject(java.io.ObjectOutputStream out)
    throws IOException;
private void readObject(java.io.ObjectInputStream in)
    throws IOException, ClassNotFoundException;

• Writing Beans to a specific file format: implement Externalizable, and its two methods:

public void writeExternal(ObjectOutput out)
    throws IOException;
public void readExternal(ObjectInput in)
    throws IOException,
    ClassNotFoundException

Methods used by event listeners

public synchronized void addMyListener(MyListener listener);
public synchronized void removeMyListener(MyListener listener);

• An alternate method can be added for Beans that can only have a single listener:

public synchronized void addMyListener(MyListener listener)
    throws TooManyListeners;

Enterprise JavaBeans (EJB)

• Server-side JavaBeans

import javax.ejb.*;
import javax.ejb.spi.*;