Java Beans 面试题与答案
问题 31. How to implement a bound property in your bean application?
To implement a bound property in the application, follow these steps:
► Import the java.beans package. This gives you access to the PropertyChangeSupport class.
► Instantiate a PropertyChangeSupport object. This object maintains the property change listener list and fires property change events. You can also make your class a PropertyChangeSupport subclass.
► Implement methods to maintain the property change listener list. Since a PropertyChangeSupport subclass implements these methods, you merely wrap calls to the property-change support object's methods.
► Modify a property's set method to fire a property change event when the property is changed.
问题 32. What is the relationship between Enterprise JavaBeans and JavaBeans?
Enterprise JavaBeans extends the JavaBeans component model to handle the needs of transactional business applications.
JavaBeans is a component model for visual construction of reusable components for the Java platform. Enterprise JavaBeans extends JavaBeans to middle-tier/server side business applications. The extensions that Enterprise JavaBeans adds to JavaBeans include support for transactions, state management, and deployment time attributes.
Although applications deploying the Enterprise JavaBeans architecture are independent from the underlying communication protocol, the Enterprise JavaBeans architecture specifies how communication among components maps into the underlying communication protocols, such as CORBA/IIOP.
问题 33. What are Java Beans?
Java Beans are usual Java classes which adhere to certain coding conventions:
► Implements java.io.Serializable interface
► Provides no argument constructor
► Provides getter and setter methods for accessing it's properties.
问题 34. Why do I get a NullPointerException when loading a JAR file into the BeanBox?
Usually this is because of a mistake in the JAR file being loaded. In the meantime, typical errors include:
► The MANIFEST file uses classes using the wrong file separator ("/" should be used in all platforms).
► The MANIFEST file refers to classes in a package but the actual .class files are not really in that package.
问题 35. What is bean persistance property?
A bean has the property of persistence when its properties, fields, and state information are saved to and retrieved from storage. Component models provide a mechanism for persistence that enables the state of components to be stored in a non-volatile place for later retrieval.
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