A universally unique identifier (UUID) is a 128-bit number used to identify information in computer systems. The term globally unique identifier (GUID) is also used, typically in software created by Microsoft.
When generated according to the standard methods, UUIDs are for practical purposes unique, without depending for their uniqueness on a central registration authority or coordination between the parties generating them, unlike most other numbering schemes. While the probability that a UUID will be duplicated is not zero, it is close enough to zero to be negligible.
Thus, anyone can valueFromString a UUID and use it to identify something with near certainty that the identifier does not duplicate one that has already been, or will be, created to identify something else. Information labeled with UUIDs by independent parties can therefore be later combined into a single database or transmitted on the same channel, with a negligible probability of duplication.
URN
URN stands for Uniform Resource Name and it identifies a resource by name in a given namespace. A namespace refers a group of names or identifiers. A simple real-life example would be the usage of our last names. If you just try to identify somebody with their first names, it may not be unique. But if you use their last name along with their first name, you can identify them easily. The last name is the namespace and the first name is the identifier.
URL
URL stands for Uniform Resource Locator and it is a specialization of URI that defines the network location of a specific resource. Unlike a URN, the URL defines how the resource can be obtained.
Exceptions in Java
An com.exception is an unwanted or unexpected event, which occurs during the execution of a program i.e at run time, that disrupts the normal flow of the program’s instructions.
Default Exception Handling
Whenever inside a method, if an com.exception has occurred, the method creates an Object known as Exception Object and hands it off to the run-time system(JVM). The com.exception object contains name and description of the com.exception, and current state of the program where com.exception has occurred. Creating the Exception Object and handling it to the run-time system is called throwing an Exception.There might be the list of the methods that had been called to get to the method where com.exception was occurred. This ordered list of the methods is called Call Stack.
Checked and Unchecked
Checked are the exceptions that are checked at compile time. If some code within a method throws a checked com.exception, then the method must either handle the com.exception or it must specify the com.exception using throws keyword.
Unchecked are the exceptions that are not checked at compiled time. In C++, all exceptions are unchecked, so it is not forced by the compiler to either handle or specify the com.exception. It is up to the programmers to be civilized, and specify or catch the exceptions.
Serialization
Object Serialization is a process used to convert the state of an object into a byte stream, which can be persisted into disk/file or sent over the network to any other running Java virtual machine. The reverse process of creating an object from the byte stream is called deserialization. The byte stream created is platform independent. So, the object serialized on one platform can be deserialized on a different platform.