Java Interfaces and I/O Streams

Java interfaces

• In Java, multiple inheritance does not exist directly, but interfaces serve a similar role
• Interfaces contain methods and variables like classes, but interfaces are fully abstract
• Multiple inheritance is disallowed in Java due to the diamond problem
• Interfaces are similar to classes, using the keyword "interface" instead of "class"
• Elements in an interface are static and final, but implementation code is not defined
• Classes can inherit from a single superclass but implement multiple interfaces
• Classes implement interfaces using specific syntax
• Interfaces enable polymorphism in Java
• Interface methods are abstract methods
• Interface methods cannot be final or static
• Interfaces cannot implement another interface or have constructors
• Interfaces can not implement classes
• Interfaces can inherit multiple other interfaces

I/O Stream

• Most programs need external data from an input source
• Programs send results to an output destination
• Input sources can be disk files, keyboards, or network sockets
• Output destinations include disk files, screens, or network connections
• Java's I/O package offers streams for input-output operations, supporting objects, data types, and files
• Java has three standard streams:

Standard Streams in Java

• System.in standard input stream used to read characters from standard input devices
• System.out standard output stream for producing program results on the computer screen
• System.err standard error stream for outputting error data on a computer screen or standard output device

Types of Streams

• Streams are divided into input and output streams based on the type of operations

Input Stream

• Input streams read data from source arrays, files, or peripheral devices with FileInputStream being an example

Output Stream

• Output streams write data into arrays, files, or output peripheral devices with FileOutputStream being an example

ByteStream

• ByteStreams process data byte by byte (8 bits)
• FileInputStream is utilized to read from a source, while FileOutputStream handles writing to the destination

CharacterStream

• Character streams automatically read/write data character by character
• FileReader and FileWriter character streams are used to read from the source and write to the destination respectively

Multithreading

• Multithreading means multiple flows of control
• Multithreading allows programs to be divided into multiple processes that can run in parallel

Advantages of Multithreading

• Programs with multiple threads improve the utilization of system resources
• Some problems are more easily solved using multiple threads

Multithreading in Java

• Java is a multithreaded language that allows multiple processes to run concurrently within a single program
• Java threads, often called lightweight threads, share the same memory space

Multitasking

• Multitasking can be process-based or thread-based

Process-Based Multitasking

• Processes are heavyweight and have separate memory areas, resulting in high communication costs and longer switching times

Thread-Based Multitasking

• Threads are lightweight, share the same address space, and have lower communication costs

Creating Threads

• Threads can be created by extending the Thread class or implementing the Runnable interface

Thread Class vs Runnable Interface

• Extending Thread class limits the class from extending other classes due to Java's lack of multiple inheritance
• Implementing Runnable allows a class to extend other base classes
• Extending Thread class provides built-in thread methods

Thread creation by extending the Thread class

• Create a class that extends the java.lang.Thread class which overrides the run() method available in the Thread class
• A thread begins its life inside run() method
• Call start() method to start the execution of a thread, start() invokes the run() in the Thread object

Thread creation by implementing the Runnable Interface

• Create a new class which implements java.lang.Runnable interface and override run() method
• Instantiate a Thread object and call start() method on this object

Life Cycle of a Thread

• Threads undergo several states during their lifetime: New, Active, Waiting/Blocked, Timed Waiting, and Terminated

New State

• A thread is in the new state when the code hasn't been run and the execution process is not initiated

Active State

• A thread goes into the active state:
  • Runnable State: It's ready to run
  • Running State: Transfers, when the thread receives CPU

Waiting/Blocked State

• A thread is in waiting/blocked state, if there is inactive but on a temporary time

Timed Waiting State

• Threads avoid starvation when the sleep() method is invoked

Terminated State

• A thread will be in terminated state due to: normal task completion, unusual events or the thread is considered dead

App development in java

• Java is used to develop applications like enterprise, network, desktop, web, and Android apps along with applets
• Java Application: A regular Java program that runs on an operating system with a virtual machine.
• Java Applet: A Java program that is embedded in a web page, running within a web browser on the client-side.

Abstract Window Tool (AWT)

• AWT (Abstract Window Toolkit) is an API for creating GUI in Java for window-based applications.
• AWT uses components like button, label, checkbox, etc
• AWT package, provides the classes

Component in AWT

• Elements such as buttons, text fields, and scroll bars are called components, you needs to add them to container

Container in AWT

• The Container is a component in AWT that can contain another components such as Window, Frame, Dialog and Panel
• It is a screen where the components are placed in it's location

Panel Container

• Panel, is the generic container for holding the components and it doesn't contain title bar, border or menu bar

Window Container

• Windor container have no borders and menu bars and to create it you must use frame or dialog

Frame

• Frame contains title bar and border and can have menu bars. It can have other components like button, text field, scrollbar etc

Java Swing

• Java Swing, a part of JFC, creates window-based applications, built on AWT
• Java Swing: unlike AWT, provides platform-independent and lightweight components.
• The javax.swing Package: offers different classes

Java AWI Vs Swing

• AWT: platform-dependent components and Swing: platform-independent components.,
• AWT: heavyweight components Vs Swing: lightweight components.
• AWT: doesn't support pluggable look and feel Vs Swing: supports pluggable look and feel
• AWT: provides less components than and Swing: more powerful components
• AWT: doesn't follows MVC and Swing: follows MVC

Java Database Connectivity (JDBC)

• JDBC (Java Database Connectivity) is a Java API used to connect and interact within databases
• JDBC is used for communicate with different database technology

JDBC

• Application: Communicate with a data source.
• JDBC API: execute SQL statements and retrieve results. - DriverManager: connect's enterprise applications to databases. - JDBC drivers: Communicate with data source.