Java Programming Concepts: A Comprehensive Guide

• A class is a template used to create objects and declare data types and methods in a program.
• Public - Modifier used to declare classes and interfaces. Void - Method that returns no value. Main - Marks the start and end of program execution.
• Scanner class - Used to get user input for types like String and Int.
• Exceptions: Try-catch block, throw statement.
• Inheritance provides a powerful and natural mechanism for organizing and structuring software programs. It improves clarity in the design of classes.
• A subclass provides specialized behavior based on elements provided by the superclass. Using inheritance, programmers can reuse the code in the superclass many times.
• Reading and Writing to Files:
  1. Import java.io file.
  2. File inputFile = new File("input.txt");
  3. File outputFile = new File("output.txt");
//outFile.delete(); // Delete output.txt
• TCP - Connection-oriented and reliable for HTTP, FTP, and Telnet. UDP - Connectionless and unreliable for SNMP and DNS.
• Port Numbers: FTP - 21; Telnet - 23; POP3 - 110; SMTP - 25; HTTP - 80; Time service - 13.
• A socket is one endpoint of a two-way communication link between two programs running on the network.
• A thread is a program unit that is executed independently of other parts of the program.
• Multithreading programming is the use of multiple threads in a single program, running at the same time and performing different tasks.
• Thread Scheduler - The thread scheduler runs each thread for a short amount of time called a time slice. Then, the scheduler picks another thread from those that are runnable.
• Concurrency is the execution of multiple tasks at the same time, regardless of the number of processors.
• Declaration for calling sleep method: InterruptedException.
• TCP Server Socket and Listening for a Connection: ServerSocket ss = new ServerSocket(PORT_NUMBER); Socket sock = ss.accept();
• Method to Find Port Number: int port = receivePacket.getPort();

Example GUI Template (Change Bold Text Accordingly)

public TextExample() {
text = new JTextField(20);
setLayout(new FlowLayout());
add(text);
}

Network Code Question

getHostName() to find cisco.com host.

Concurrency

Concurrency is the execution of multiple tasks at the same time, regardless of the number of processors.

A Concurrent System is one in which:

• Multiple tasks can be executed at the same time.
• The tasks may be duplicates of each other or distinct tasks.
• The overall time to perform the series of tasks is reduced.

Advantages of Concurrency

• Concurrent processes can reduce code duplication.
• The overall runtime of the algorithm can be significantly reduced.
• More real-world problems can be solved than with sequential algorithms alone.
• Redundancy can make systems more reliable.

Disadvantages of Concurrency

• Runtime is not always reduced, so careful planning and task scheduling are required.
• Concurrent algorithms can be more complex than sequential algorithms.
• Shared data can be corrupted and deadlocked.
• Communication between tasks is needed.

Throw and Catch

1. You throw an exception to notify some other part of the program that an exceptional condition has occurred.
2. You catch an exception to handle an exceptional situation that has occurred elsewhere in the program.
3. If an exception has no matching catch clause in the same method, the search for a matching catch clause continues in the calling method. If the entire program has no matching catch clause, then the program terminates.

Asymmetric Encryption

Asymmetric (or "public key") encryption is a much more complex process than symmetric encryption and carries a large processing overhead for the machines concerned.