Java Interview Questions 2
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- What is a servlet lifecycle?
- It defines how the servlet is loaded and initialized. How it receives and responds to requests, and how it is taken out of service. It is defined by the javax.servlet.Servlet interface.
- How do servlets differ from applets?
- Servlets do not run in a web browser with a Graphical User Interface. Instead they interact with the servlet engine running on the Web Server through requests and responses. The request-response paradigm is modeled on the behavior of HTTP.
- Define a java servlet?
- Java Servlets are small, platform, independent Java programs that can be used to extend the functionality of a Web Server in a variety of ways.
- What is J2EE Connector?
- The J2EE Connector API is used by J2EE tools vendors and system integrators to create resource adapters that support access to enterprise information systems that can be plugged into any J2EE product. Each type of database or EIS has a different resource adapter. Note: A resource adapter is a software component that allows J2EE application components to access and interact with the underlying resource manager. Because a resource adapter is specific to its resource manager, there is typically a different resource adapter for each type of database or enterprise information system.
- How is the MVC design pattern used in Struts framework?
- In the MVC design pattern, application flow is mediated by a central Controller. The Controller delegates requests to an appropriate handler. The handlers are tied to a Model, and each handler acts as an adapter between the request and the Model. The Model represents, or encapsulates, an applicationÂ’s business logic or state. Control is usually then forwarded back through the Controller to the appropriate View. The forwarding can be determined by consulting a set of mappings, usually loaded from a database or configuration file. This provides a loose coupling between the View and Model, which can make an application significantly easier to create and maintain. Controller: Servlet controller which supplied by Struts itself; View: what you can see on the screen, a JSP page and presentation components; Model: System state and a business logic JavaBeans.
- What is Struts?
- A Web page development framework. Struts combines Java Servlets, Java Server Pages, custom tags, and message resources into a unified framework. It is a cooperative, synergistic platform, suitable for development teams, independent developers, and everyone between.
- What is the EAR file?
- An EAR file is a standard JAR file with an .ear extension, named from Enterprise ARchive file. A J2EE application with all of its modules is delivered in EAR file.
- What is J2EE?
- J2EE is an environment for developing and deploying enterprise applications. The J2EE platform consists of a set of services, application programming interfaces (APIs), and protocols that provide the functionality for developing multitiered, web-based applications.
- What is polymorphism?
- Polymorphism allows methods to be written that needn't be concerned about the specifics of the objects they will be applied to. That is, the method can be specified at a higher level of abstraction and can be counted on to work even on objects of yet unconceived classes.
- What is tunnelling?
- Tunnelling is a route to somewhere. For example, RMI tunnelling is a way to make RMI application get through firewall. In CS world, tunnelling means a way to transfer data.
- What is Serialization and deserialization?
- Serialization is the process of writing the state of an object to a byte stream.
- What are the Object and Class classes used for?
- The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.
- What is casting?
- There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
- What restrictions are placed on method overriding?
- Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
- What restrictions are placed on method overloading?
- Two methods may not have the same name and argument list but different return types.
- How does multithreading take place on a computer with a single CPU?
- The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
- What is the difference between static and non-static variables?
- A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.
- If a class is declared without any access modifiers, where may the class be accessed?
- A class that is declared without any access modifiers is said to have package or friendly access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.
- What classes of exceptions may be caught by a catch clause?
- A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.
- What happens when a thread cannot acquire a lock on an object?
- If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.
- What is a protected method?
- A protected method is a method that can be accessed by any method in its package and inherited by any subclass of its class.
- What is a static method?
- A static method is a method that belongs to the class rather than any object of the class and doesn't apply to an object or even require that any objects of the class have been instantiated.
- What is an abstract method?
- An abstract method is a method whose implementation is deferred to a subclass. Or, a method that has no implementation (an interface of a method).
- What is the purpose of finalization?
- The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.
- How does Java handle integer overflows and underflows?
- It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
- What state does a thread enter when it terminates its processing?
- When a thread terminates its processing, it enters the dead state.
- What are three ways in which a thread can enter the waiting state?
- A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.
- What are synchronized methods and synchronized statements?
- Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
- What is synchronization and why is it important?
- With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often causes dirty data and leads to significant errors.
- What is a transient variable?
- A transient variable is a variable that may not be serialized. If you don't want some field not to be serialized, you can mark that field transient or static.
- What is the serialization?
- The serialization is a kind of mechanism that makes a class or a bean persistence by having its properties or fields and state information saved and restored to and from storage.
- What is native code?
- The native code is code that after you compile it, the compiled code runs on a specific hardware platform.
- What is the package?
- The package is a Java namespace or part of Java libraries. The Java API is grouped into libraries of related classes and interfaces; these libraries are known as packages.
- What is the Java API?
- The Java API is a large collection of ready-made software components that provide many useful capabilities, such as graphical user interface (GUI) widgets.