JDBC is an abstraction layer that allows users to choose between databases. JDBC enables developers to write database applications in Java without having to concern themselves with the underlying details of a particular database.

A Java virtual machine (JVM) is a process virtual machine that can execute Java bytecode.

Each Java source file is compiled into a bytecode file, which is executed by the JVM. Java was designed to allow application programs to be built that could be run on any platform, without having to be rewritten or recompiled by the programmer for each separate platform.

A Java virtual machine makes this possible because it is aware of the specific instruction lengths and other particularities of the underlying hardware platform.

Java has two types of exceptions: checked exceptions and unchecked exceptions.

1. Unchecked exceptions do not need to be declared in a method or a constructor’s throws clause if they can be thrown by the execution of the method or the constructor, and propagate outside the method or constructor boundary.

2. On the other hand, checked exceptions must be declared in a method or a constructor’s throws clause.

The servlet is a Java programming language class used to process client requests and generate dynamic web content.

Servlets are mostly used to process or store data submitted by an HTML form, provide dynamic content and manage state information that does not exist in the stateless HTTP protocol.

• The Java Runtime Environment (JRE) is basically the Java Virtual Machine (JVM) where your Java programs are being executed. It also includes browser plugins for applet execution.

• The Java Development Kit (JDK) is the full-featured Software Development Kit for Java, including the JRE, the compilers, and tools (like JavaDoc, and Java Debugger), in order for a user to develop, compile and execute Java applications.

• Applets are executed within a Java-enabled browser.

• Java application is a standalone Java program that can be executed outside of a browser.

However, they both require the existence of a Java Virtual Machine (JVM). Furthermore, a Java application requires a main method with a specific signature, in order to start its execution. Java applets don’t need such a method to start their execution. Finally, Java applets typically use a restrictive security policy, while Java applications usually use more relaxed security policies.

A Java Server Page (JSP) is a text document that contains two types of text:

• static data and

• JSP elements.

Static data can be expressed in any text-based format, such as HTML or XML. JSP is a technology that mixes static content with dynamically-generated content.