1 Introduction to Programming

1.1 What is programming

• Programming involves creating applications such as ticketing kiosks, games, restaurant ordering systems, and various other business applications.
• It is considered a scientific discipline, where logic and algorithms are used to solve real-world problems.
• Many techniques and programming languages have been developed for accomplishing fundamental programming tasks, catering to a wide range of application domains.
• Software engineering practices play a crucial role in ensuring that programs are correct, reliable, and maintainable over time.
• Programming is not just about science; it is also a creative endeavor, as programmers design innovative solutions to unique challenges.
• Programmers have the opportunity to tackle complex problems and devise efficient and elegant solutions, making programming a problem-solving activity.

1.2 Programming languages

Machine language

• Machine language is the lowest-level programming language understood directly by a computer's central processing unit (CPU).
• It consists of binary code or hexadecimal instructions that represent specific operations, such as arithmetic calculations and memory manipulations.
• Each computer architecture has its own unique machine language, tailored to its CPU design.
• Machine language instructions are executed very quickly by the CPU, making it the most efficient form of programming.
• Programmers rarely write code directly in machine language due to its complexity and lack of human-friendliness.
• Instead, higher-level programming languages like C, C++, and Java are used, and compilers or assemblers convert their code into machine language.
• Machine language instructions typically include operations like load, store, add, subtract, jump, and compare.
• Understanding and programming in machine language requires deep knowledge of a specific CPU's instruction set and memory architecture.

Assembly language

• Assembly language is a low-level programming language that is a step above machine language.
• It uses mnemonic codes and symbols to represent machine instructions, making it more human-readable than pure machine language.
• Each assembly language is specific to a particular computer architecture or CPU, as it directly corresponds to the CPU's instruction set.
• Programmers write code in assembly language to interact with a computer's hardware and control its operations at a detailed level.
• Assembly language provides a bridge between high-level programming languages and machine language, allowing for more human-friendly programming while still offering fine-grained control.
• Assembly programs are translated into machine language through an assembler, which generates binary machine code.
• Programmers use assembly language for tasks that require precise control over hardware, such as writing device drivers, firmware, or optimizing critical sections of code.
• Assembly language programming requires a deep understanding of the specific CPU's architecture, instruction set, and memory layout.
• Debugging and maintaining assembly code can be challenging due to its low-level nature, but it can result in highly efficient and optimized programs.

High-level languages

• High-level programming languages are designed to be more human-readable and user-friendly than low-level languages like assembly or machine code.
• They use English-like keywords and syntax that abstract away the underlying hardware details, making programming more accessible.
• High-level languages include popular languages like Python, Java, C++, and JavaScript, among others.
• Programmers write code in high-level languages to solve complex problems and build a wide range of applications, from web applications to scientific simulations.
• High-level languages are platform-independent, allowing code to run on different computer architectures with minimal modification, thanks to compilers or interpreters.
• These languages offer a wide variety of built-in functions and libraries that simplify common tasks, reducing development time.
• Debugging and maintenance of code written in high-level languages are typically easier compared to low-level languages, thanks to their abstraction.
• High-level languages support features like object-oriented programming, which helps organize code and promote code reusability.
• They often come with strong community support, extensive documentation, and a wealth of third-party libraries, making development more efficient.

1.3 Problem solving

Problem-Solving Approach:

• The key to effective problem-solving is guiding your thought process. Continuously asking "What if we did it this way?" is a valuable approach to explore different solutions.
• Exploring various ways to solve a problem is essential for finding the most optimal solution.

Understanding the Problem:

• Understanding the problem thoroughly is a crucial first step in problem-solving.
• To achieve a complete understanding, consider:
• Identifying the inputs required for the problem.
• Determining the expected outputs.
• Establishing the correct sequence of instructions.
• Identifying decision points within the problem.
• Recognizing any repeating patterns or areas in the problem.

Designing an Algorithm:

• An algorithm is a step-by-step sequence of instructions used to accomplish a specific task.
• Algorithms can be presented in different formats, including:
  • Structured code, often represented using pseudocode.
  • Flowcharts, which provide a visual representation of the algorithm's logic.

1.3.1 Pseudocode

Pseudocode Overview:

• Pseudocode is a high-level description of an algorithm that uses a mix of human-readable language and basic programming constructs.
• It is used to outline the logic of a program or algorithm before actual coding begins.
• Pseudocode is not tied to any specific programming language and is a useful tool for planning and communication in software development.
• Pseudocode is meant to be readable and understandable by both programmers and non-programmers.
• It provides a high-level view of the algorithm's logic without getting into specific syntax or implementation details.
• Pseudocode allows for easy collaboration and planning during the initial stages of software development.
• It is a valuable tool for breaking down complex problems into smaller, manageable steps before coding.

Pseudocode Examples:

Input two numbers, num1 and num2
Initialize a variable sum to 0
Add num1 to sum
Add num2 to sum
Output sum

1.3.2 FLow chart

Overview:

• A flowchart is a graphical representation of a process or algorithm using symbols and connecting arrows.
• It provides a visual way to depict the flow of control and data within a program.
• Flowcharts are used for planning, designing, and documenting algorithms and processes.

Flowchart Symbols:

• Start/End Symbol: Represents the beginning and end of a process or algorithm.
• Process Symbol: Depicts an operation or action to be performed.
• Input/Output Symbol: Signifies data input or output.
• Decision Symbol (Diamond): Represents a decision or branching point in the flow.
• Connector Symbol (Circle): Indicates a point where the flowchart connects to another part of the chart.
• Flow Arrows: Arrows connecting symbols show the flow of control or data.

1.4 What is Java

• Combination of compiler and interpreter
• The compiler converts source code into byte codes (an instruction set for a virtual, machine-independent processor)
• At run time, the Java Virtual Machine (JVM) interprets the byte codes and converts them into the machine language for the platform on which the program is running.
• Created by Sun Microsystems in 1995
• Syntax is based on C++
• Object-oriented
• Supports Internet applications
• Provides an extensive library of prewritten classes
• Is portable among platforms
• Has built-in networking

Applet:

• An Applet is a Java program that runs in a web browser.
• It is a small Java application that is embedded within an HTML page.
• Applets are primarily used for creating dynamic and interactive web content.
• They follow the applet lifecycle, including methods like init(), start(), stop(), and destroy().
• Applets have limited access to the system and are mainly used for client-side processing.

Servlet:

• A Servlet is a Java program that runs on the server side.
• Servlets are used for processing requests and generating responses in a web application.
• They extend the javax.servlet.Servlet interface and handle HTTP requests and responses.
• Servlets are highly scalable and can handle multiple requests concurrently.
• They are typically part of a Java web application, often packaged in a WAR (Web Application Archive) file.

Application in Java:

• A Java Application is a standalone program written in Java. It is not embedded in a web browser or part of a web application.
• Java applications are typically started with a main method.
• They can perform various tasks, from simple command-line utilities to complex desktop applications.
• Java applications have access to the full range of Java libraries and can interact with the system and user interface.

1.5 Object-Oriented Programming (OOP)

OOP Overview:

• Object-Oriented Programming (OOP) is a programming paradigm that organizes code into objects, which are instances of classes.
• It emphasizes the modeling of real-world entities and their interactions in code.
• OOP is based on four core principles: encapsulation, inheritance, polymorphism, and abstraction.

Key OOP Concepts:

• Classes: Blueprint or template for creating objects. Define attributes (data) and methods (functions) for objects.
• Objects: Instances of classes that encapsulate both data (attributes) and behaviours (methods).
• Encapsulation: The practice of hiding the internal details of an object and exposing only what's necessary through well-defined interfaces.
• Inheritance: A mechanism that allows a new class (subclass or derived class) to inherit properties and behaviors from an existing class (superclass or base class).
• Polymorphism: The ability for different classes to be treated as instances of a common base class, enabling flexibility and extensibility in code.
• Abstraction: Simplifying complex systems by modeling them with a focus on the essential properties and behaviors, while hiding unnecessary details.

Benefits of OOP:

• Modularity: OOP promotes modular code, making it easier to understand, maintain, and reuse.
• Code Reusability: Inheritance and polymorphism enable the reuse of code and the creation of hierarchical class structures.
• Flexibility: OOP supports dynamic and flexible coding through polymorphism and encapsulation.
• Scalability: OOP facilitates the creation of large and complex systems by breaking them down into manageable objects and classes.

Examples of OOP Languages:

• Java, C++, Python, C#, and Ruby are popular programming languages that support OOP.
• Each of these languages provides syntax and features for creating and working with objects and classes.

Applications of OOP:

• OOP is widely used in software development for building applications, games, web services, and more.
• It is particularly well-suited for modeling complex systems with a clear and organized structure.

1.6 Programming Basics

• Programming is translating a problem into ordered steps consisting of operations a computer can perform:
  • Input
  • Perform calculations
  • Compare values
  • Move data
  • Output
• The order of execution of instructions is called the flow of control

1.7 Types of Flow of Control

1 Sequential Processing

Execute instructions in order

Example

The pseudocode for calculating the sum of two numbers would look like this:

	read first number
	read second number
	set total to (first number +second number)
  output total

2 Method Call

Jump to code in method, then return Calling the method executes the method Methods can take arguments (data to use) and return values

Example

Here is pseudocode for calculating the square root of an integer:

read an integer
 call the square root method,  passing the integer and receiving the square root
output the square root

3 Selection

Choose code to execute based on data value

Example

The pseudocode for determining if a number is positive or negative is:

 read a number
	if the number is greater thanor equal to 0
	  write "Number is positive."
  else
	  write "Number is negative." 

4 Looping or Iteration

Repeat operations for multiple data values

Example

The pseudocode for finding the sum of a set of numbers is:

 set total to 0
 read a number
 while there was a number to  read,
	 add number to total
	 read the next number
 write total

Important points to consider

• Java is case-sensitive.
• The source file must be saved with the same name as the class name with a .java extension.
• The class name and the source filename must match exactly, including capitalization.

Error Types

Compiler errors

• Found by the compiler
• Usually caused by incorrect syntax or spelling

Run-time errors

• Reported by the JVM
• Usually caused by incorrect use of prewritten classes or invalid data

Logic errors

• Found by testing the program
• Incorrect program design or incorrect execution of the design