What is the difference between an Applet and an Application?
A Java application is made up of a main() method declared as public static void that accepts a string array argument, along with any other classes that main() calls. It lives in the environment that the host OS provides. A Java applet is made up of at least one public class that has to be subclassed from java.awt.Applet. The applet is confined to living in the user's Web browser, and the browser's security rules, (or Sun's appletviewer, which has fewer restrictions). The differences between an applet and an application are as follows:
1. Applets can be embedded in HTML pages and downloaded over the Internet whereas Applications have no special support in HTML for embedding or downloading.
2. Applets can only be executed inside a java compatible container, such as a browser or appletviewer whereas Applications are executed at command line by java.exe or jview.exe.
3. Applets execute under strict security limitations that disallow certain operations(sandbox model security) whereas Applications have no inherent security restrictions.
4. Applets don't have the main() method as in applications. Instead they operate on an entirely different mechanism where they are initialized by init(),started by start(),stopped by stop() or destroyed by destroy().
Java says "write once, run anywhere". What are some ways this isn't quite true?
As long as all implementaions of java are certified by sun as 100% pure java this promise of "Write once, Run everywhere" will hold true. But as soon as various java core implemenations start digressing from each other, this won't be true anymore. A recent example of a questionable business tactic is the surreptitious behavior and interface modification of some of Java's core classes in their own implementation of Java. Programmers who do not recognize these undocumented changes can build their applications expecting them to run anywhere that Java can be found, only to discover that their code works only on Microsoft's own Virtual Machine, which is only available on Microsoft's own operating systems.
What is the difference between a Vector and an Array. Discuss the advantages and disadvantages of both?
Vector can contain objects of different types whereas array can contain objects only of a single type.
- Vector can expand at run-time, while array length is fixed.
- Vector methods are synchronized while Array methods are not
What are java beans?
JavaBeans is a portable, platform-independent component model written in the Java programming language, developed in collaboration with industry leaders. It enables developers to write reusable components once and run them anywhere — benefiting from the platform-independent power of Java technology. JavaBeans acts as a Bridge between proprietary component models and provides a seamless and powerful means for developers to build components that run in ActiveX container applications. JavaBeans are usual Java classes which adhere to certain coding conventions:
1. Implements java.io.Serializable interface
2. Provides no argument constructor
3. Provides getter and setter methods for accessing it's properties
What is RMI?
RMI stands for Remote Method Invocation. Traditional approaches to executing code on other machines across a network have been confusing as well as tedious and error-prone to implement. The nicest way to think about this problem is that some object happens to live on another machine, and that you can send a message to the remote object and get a result as if the object lived on your local machine. This simplification is exactly what Java Remote Method Invocation (RMI) allows you to do. Above excerpt is from "Thinking in java". For more information refer to any book on Java.
What does the keyword "synchronize" mean in java. When do you use it? What are the disadvantages of synchronization?
Synchronize is used when you want to make your methods thread safe. The disadvantage of synchronize is it will end up in slowing down the program. Also if not handled properly it will end up in dead lock.
What gives java it's "write once and run anywhere" nature?
Java is compiled to be a byte code which is the intermediate language between source code and machine code. This byte code is not platorm specific and hence can be fed to any platform. After being fed to the JVM, which is specific to a particular operating system, the code platform specific machine code is generated thus making java platform independent.
What are native methods? How do you use them?
Native methods are methods written in other languages like C, C++, or even assembly language. You can call native methods from Java using JNI. Native methods are used when the implementation of a particular method is present in language other than Java say C, C++. To use the native methods in java we use the keyword native
public native method_a(). This native keyword is signal to the java compiler that the implementation of this method is in a language other than java. Native methods are used when we realize that it would take up a lot of rework to write that piece of already existing code in other language to Java.
What is JDBC? Describe the steps needed to execute a SQL query using JDBC.
We can connect to databases from java using JDBC. It stands for Java DataBase Connectivity.
Here are the steps:
1. Register the jdbc driver with the driver manager
2. Establish jdbc connection
3. Execute an sql statement
4. Process the results
5. Close the connection
Before doing these do import java.sql.*
JDBC is java based API for accessing data from the relational databases. JDBC provides a set of classes and interfaces for doing various database operations. The steps are:
Register/load the jdbc driver with the driver manager.
Establish the connection thru DriverManager.getConnection();
Fire a SQL thru conn.executeStatement();
Fetch the results in a result set
Process the results
Close statement/result set and connection object.
