Short notes on 1. Vector 2. JAR 3. Super and final keyword 4. J2EE

1. Vector: Vector is a legacy collection class in Java that is similar to ArrayList, but it is synchronized, which means that it is thread-safe. Vectors store elements in an ordered sequence and allow random access to the elements. Vectors also automatically grow or shrink as needed to accommodate the number of elements stored in them. However, due to their synchronization overhead, Vectors are less efficient than ArrayLists for single-threaded applications.

2. JAR: JAR stands for Java Archive, which is a file format used to package Java class files, resources, and metadata into a single archive file. JAR files are used to distribute Java libraries, applications, and applets. JAR files can be signed with a digital certificate to ensure their authenticity and integrity.

3. Super and final keyword: super is a keyword in Java that refers to the superclass of a subclass. It is used to call a method or constructor of the superclass from within the subclass. The final keyword is used to make a class, method, or variable unmodifiable, meaning that its value or behavior cannot be changed once it has been set. A final class cannot be subclassed, a final method cannot be overridden, and a final variable cannot be reassigned.

4. J2EE: J2EE stands for Java 2 Enterprise Edition, which is a set of Java technologies and APIs used for building enterprise-level distributed applications. J2EE includes a number of component technologies, such as servlets, JavaServer Pages (JSP), Enterprise JavaBeans (EJB), Java Message Service (JMS), Java Naming and Directory Interface (JNDI), Java Transaction API (JTA), and JavaMail. J2EE provides a standard platform for developing, deploying, and managing enterprise applications, and it is widely used in the industry for building large-scale, mission-critical systems.