OOP's using JAVA NOTES ( OBJECT ORIENTED PROGRAMMING USING JAVA SHORT NOTES)

CHAPTER 1

Basics of Java:

• What is Java: Java is a high-level, object-oriented programming language developed by Sun Microsystems (now owned by Oracle Corporation). It's known for its "Write Once, Run Anywhere" capability, which means code written in Java can run on different platforms without modification.
• Key Features: Java is known for its simplicity, portability, and robustness. It supports multi-threading, which allows concurrent execution of tasks, and has a vast standard library.

2. Background/History of Java:

• Origins: Java was created by James Gosling, Mike Sheridan, and Patrick Naughton at Sun Microsystems in the mid-1990s.
• Objective: The initial goal of Java was to develop a programming language for consumer electronics. It was originally named "Oak" but was later renamed to Java.
• Significant Events: In 1995, Sun Microsystems released Java 1.0, which gained popularity due to its platform-independence.

3. Java and the Internet:

• Applets: Java's ability to run code in a web browser made it popular for creating applets, small programs that could be embedded in web pages.
• Server-Side Java: Java is used extensively for server-side programming, powering many web applications and services. Technologies like Java Servlets and JSP (JavaServer Pages) facilitate web development.

4. Advantages of Java:

• Platform Independence: Java code can run on any platform with a Java Virtual Machine (JVM), making it highly portable.
• Object-Oriented: Java is based on the object-oriented programming (OOP) paradigm, promoting code reusability and maintainability.
• Security: Java has built-in security features to protect against malicious code.
• Large Standard Library: Java offers a comprehensive library of classes and APIs for various tasks, reducing the need for reinventing the wheel.
• Multi-Threading: Java supports multi-threading, enabling concurrent execution and better performance.

5. Java Virtual Machine & Byte Code:

• Java Virtual Machine (JVM): JVM is a key component of Java's platform independence. It's an execution environment that interprets Java bytecode and translates it into native machine code. Different platforms have their own JVM implementations.
• Bytecode: Java source code is compiled into an intermediate form called bytecode. This bytecode is platform-independent and can be executed by any JVM. It ensures that Java code can run on various platforms without modification.

6. Java Environment Setup:

• Installing Java: To develop and run Java programs, you need to install the Java Development Kit (JDK) on your system. The JDK includes the Java compiler (javac) and other tools.
• IDEs: Integrated Development Environments (IDEs) like Eclipse, IntelliJ IDEA, and NetBeans provide a user-friendly environment for Java development.
• Setting Up the PATH: After installing Java, you should set up the PATH environment variable to access Java tools and executables from the command line.
• Code Compilation: Use the javac command to compile Java source code files (.java) into bytecode (.class). To run a Java program, use the java command followed by the class name.

1. Java Program Structure:

• A Java program typically consists of classes, methods, and statements.
• The program must have a main method, which serves as the entry point.
• Statements are executed in order, from top to bottom, unless control flow statements (if, for, while, etc.) are used.

2. Procedure-Oriented vs. Object-Oriented Programming Concept:

• Procedure-Oriented Programming (POP): In POP, programs are organized around procedures or functions. Data is usually global and can be accessed by any part of the program.
• Object-Oriented Programming (OOP): In OOP, programs are organized around objects, which encapsulate data and behavior. It promotes modularity and encapsulation.

1. Organization:

   • In POP, code is organized around procedures or functions. These procedures are essentially a set of instructions that are executed in a sequential manner.
   • Data is typically global and can be accessed by any part of the program. Data and functions are separate entities.

2. Data Handling:

   • Data is usually structured as records or data structures that store related pieces of information.
   • Functions operate on this data and can modify it directly.

3. Code Reusability:

   • Code reusability is limited because functions are specific to a particular program, and they may not be easily adaptable to other contexts.

4. Encapsulation:

   • POP does not inherently support encapsulation, meaning that data and the functions that operate on it are not necessarily bundled together as a single unit.

5. Example Languages:

   • Examples of languages that follow the POP paradigm include C and Pascal.

Object-Oriented Programming (OOP):

1. Organization:

   • In OOP, code is organized around objects, which are instances of classes. Objects encapsulate both data (attributes) and behavior (methods).
   • The program is divided into objects that communicate and interact with each other.

2. Data Handling:

   • Data is encapsulated within objects, and access to this data is typically controlled through methods, providing better data security.
   • Objects can communicate with each other by invoking methods.

3. Code Reusability:

   • OOP promotes code reusability through the concept of inheritance. Subclasses can inherit and extend the properties and behaviors of superclasses.

4. Encapsulation:

   • Encapsulation is a fundamental concept in OOP. It involves bundling data and the methods that operate on that data within a single unit called a class. This hides the internal details and provides a clear interface to the data.

5. Example Languages:

   • Examples of languages that follow the OOP paradigm include Java, C++, and Python.

Key Differences:

• Abstraction: OOP provides a higher level of abstraction through objects and classes, making it easier to model real-world entities.
• Data Security: OOP enforces better data security through encapsulation and access control mechanisms.
• Code Reusability: OOP promotes code reusability through inheritance and polymorphism, which allows objects of different classes to be treated as objects of a common superclass.
• Complexity Management: OOP can help manage the complexity of large software systems by organizing code around related objects and their interactions.

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3. Basics of OOP:

• Abstraction: Abstraction is the process of simplifying complex systems by breaking them into smaller, manageable parts (classes and objects).
• Inheritance: Inheritance allows a new class (subclass) to inherit properties and behaviors from an existing class (superclass).
• Encapsulation: Encapsulation is the concept of hiding the internal details of an object and exposing only the necessary functionality through methods.
• Classes, Subclasses, and Superclasses: A class is a blueprint for creating objects. A subclass inherits properties and methods from a superclass. Subclasses can add or override behavior.
• Polymorphism and Overloading: Polymorphism allows objects of different classes to be treated as objects of a common superclass. Method overloading involves defining multiple methods with the same name but different parameters.

4. Message Communication:

• In OOP, objects communicate by sending messages to each other. A message is a method call on an object.
• Objects can interact by invoking methods on other objects, and these interactions facilitate the execution of tasks.

5. Compiling and Running a Simple "Hello World" Program:

• Setting Up Your Computer:

  • Install the Java Development Kit (JDK) to compile and run Java programs.
  • Set up the PATH environment variable to access Java and javac from the command line.

• Writing a Program:

  • Create a Java source code file with a .java extension.
  • Define a class with a main method that prints "Hello, World!" to the console.

• Compiling, Interpreting, and Running the Program:

  • Use the javac command to compile the .java file into bytecode (.class).
  • Use the java command followed by the class name to execute the program.

• Common Errors:

  • Syntax Errors: Mistakes in the code that violate the language's rules.
  • Logic Errors: Code that compiles and runs but produces incorrect results.
  • Runtime Errors: Errors that occur during program execution, such as division by zero.

CHAPTER-2

1. Primitive Data Types:

• Integers: These data types represent whole numbers. Common integer types include byte, short, int, and long, with varying ranges.
• Floating-Point Types: These data types represent numbers with decimal points. Common floating-point types include float and double.
• Characters: The char data type represents a single character and uses the Unicode character set.
• Booleans: The boolean data type can have only two values: true and false.

2. User-Defined Data Types:

• User-defined data types are created by the programmer. These can include classes, structures, or enums. Classes, in particular, are at the core of object-oriented programming and are used to define objects and their behavior.

3. Identifiers & Literals:

• Identifiers: These are names used for variables, classes, methods, etc. Identifiers must start with a letter, underscore, or dollar sign and can contain letters, digits, underscores, and dollar signs.
• Literals: Literals are constant values used directly in code. Examples include integer literals like 5, string literals like "Hello", and character literals like 'A'.

4. Declarations of Constants & Variables:

• Constants are declared using the final keyword in Java. For example: final int MAX_VALUE = 100;.
• Variables are declared by specifying their data type, name, and optionally an initial value. For example: int count = 0;.

5. Type Conversion and Casting:

• Type conversion (or casting) involves changing the data type of a value. It can be implicit (e.g., from int to double) or explicit (e.g., (int) casting in Java).
• Explicit casting may result in data loss if the target type cannot represent the value.

6. Scope of Variables & Default Values of Variables Declared:

• Variables in a program have a scope, which defines where they are accessible. Common scopes include local (within a method), instance (inside a class but outside methods), and class (static variables).
• The default values of variables in Java are typically 0 for numeric types, false for boolean, and null for objects.

7. Wrapper Classes:

• Wrapper classes in Java (e.g., Integer, Double) are used to convert primitive data types into objects and provide utility methods for working with those types. They are essential for using data structures like collections that require objects.

8. Comment Syntax:

• Comments are used to document code and are ignored by the compiler. In Java, there are two main types of comments:
  • Single-line comments: // This is a single-line comment.
  • Multi-line comments: /* This is a multi-line comment. */

9. Garbage Collection:

• Garbage collection is a process in which the programming language automatically reclaims memory that is no longer in use by the program.
• In Java, the Java Virtual Machine (JVM) manages garbage collection, freeing up memory occupied by objects that are no longer referenced by the program.

Understanding these topics is crucial for effectively working with data in Java and ensuring that your code is organized and well-documented. It's also essential for memory management in garbage-collected languages like Java.

CHAPTER-3

1. Arrays of Primitive Data Types:

• An array is a data structure that stores a collection of elements of the same data type.
• Arrays can be of primitive data types (int, float, char, etc.), and each element in the array is accessed by an index.
• Example in Java:
• int[] myArray = new int[5]; // Declare an array of 5 integers myArray[0] = 10; // Assign a value to the first element

2. Types of Arrays:

• Arrays can be categorized as one-dimensional, two-dimensional, and multidimensional.
• One-dimensional arrays are lists, while two-dimensional arrays are like tables or matrices.
• Multidimensional arrays can have more than two dimensions.
• Example in Java:
• int[] oneDimensionalArray = new int[5]; int[][] twoDimensionalArray = new int[3][3];

3. Creation, Concatenation, and Conversion of Strings:

• Strings are sequences of characters.
• Creation: You can create strings using double quotes or string constructor.
• Concatenation: Combining strings using the + operator or concat method.
• Conversion: You can convert between strings and other data types.
• Example in Java:
• String str1 = "Hello"; String str2 = new String("World"); String combined = str1 + " " + str2; // Concatenation int num = 42; String strNum = Integer.toString(num); // Conversion to string

hanging Case of Strings:

• Strings can be converted to uppercase or lowercase using toUpperCase() and toLowerCase() methods.
• Example in Java:
• String original = "Hello, World!"; String lowerCase = original.toLowerCase(); // Converts to lowercase String upperCase = original.toUpperCase(); // Converts to uppercase

Character Extraction:

• You can extract individual characters from a string by using the charAt() method.
• Example in Java:

String text = "Example";

char firstChar = text.charAt(0); // Gets the first character ('E')

String Comparison:

• You can compare strings using equals(), equalsIgnoreCase(), or compare by character.
• Use equals() for case-sensitive comparisons and equalsIgnoreCase() for case-insensitive comparisons.
• Example in Java:

String str1 = "hello"; String str2 = "Hello"; boolean isEqual = str1.equals(str2); // false boolean isEqualIgnoreCase = str1.equalsIgnoreCase(str2); // true

StringBuffer:

• In Java, StringBuffer is a mutable sequence of characters.
• It allows for efficient string manipulation, such as appending or inserting characters.
• Example in Java:

• StringBuffer:

• In Java, StringBuffer is a mutable sequence of characters.
• It allows for efficient string manipulation, such as appending or inserting characters.
• StringBuffer operations

• StringBuffer is a class in Java that provides a mutable sequence of characters. Unlike the regular String class, which is immutable (cannot be changed after creation), StringBuffer allows you to modify the content of the string. Here are some common operations and methods you can perform with StringBuffer:

  1. Initialization:

  • You can create a new StringBuffer object and initialize it with a string or an initial capacity.
  • StringBuffer buffer1 = new StringBuffer(); // Empty buffer StringBuffer buffer2 = new StringBuffer("Hello"); // Initialized with "Hello" StringBuffer buffer3 = new StringBuffer(20); // Initial capacity of 20 characters
  
  

• Append:

  • The append() method is used to add characters, strings, or other data types to the end of the existing content in the buffer.
  • StringBuffer buffer = new StringBuffer("Hello"); buffer.append(" World"); // Appends " World" to the existing buffer

  
  

• Insert:

  • The insert() method allows you to insert characters, strings, or other data types at a specified position in the buffer.
  • StringBuffer buffer = new StringBuffer("Hello"); buffer.insert(5, " World"); // Inserts " World" after the 5th position

  
  

• Delete:

  • The delete() method removes characters from the buffer based on the specified indices.
  • StringBuffer buffer = new StringBuffer("Hello World"); buffer.delete(6, 11); // Deletes "World" from the buffer

  Replace:

  • The replace() method allows you to replace characters in the buffer with new characters or strings.
  • StringBuffer buffer = new StringBuffer("Hello World"); buffer.replace(6, 11, "Universe"); // Replaces "World" with "Universe"

  
  

Decision and control statements are essential constructs in programming languages that enable you to control the flow of your code based on certain conditions or loops. In this explanation, we'll cover these statements in detail:

1. Selection Statements:

• if Statement:

• The if statement allows you to execute a block of code if a specified condition is true.
• It has an optional else block that executes when the condition is false.

if (condition) {

    // Code to execute if the condition is true

} else {

    // Code to execute if the condition is false

}

if...else if...else Statement:

• This statement allows you to handle multiple conditions sequentially.
• if (condition1) { // Code for condition1 } else if (condition2) { // Code for condition2 } else { // Code if no conditions are met }

switch Statement:

• The switch statement is used for multiple branches of code based on the value of an expression.
• It is often used for cases where you want to compare a single value against multiple possibilities.

switch (expression) { case value1: // Code for value1 break; case value2: // Code for value2 break; default: // Code if none of the cases match }

Loops:

• while Loop:

• The while loop repeatedly executes a block of code as long as a specified condition is true.

while (condition) { // Code to execute while the condition is true }

do-while Loop:

• The do-while loop is similar to the while loop but ensures that the code block is executed at least once before the condition is checked.

do { // Code to execute } while (condition);

for Loop:

• The for loop is used to iterate a specific number of times.
• It consists of an initialization, a condition, and an update statement.

for (initialization; condition; update) { // Code to execute }

Jump Statements:

• break Statement:

• The break statement is used to exit a loop prematurely. It is commonly used to terminate a loop when a certain condition is met.
• for (int i = 0; i < 10; i++) { if (i == 5) { break; // Exit the loop when i is 5 } }

continue Statement:

• The continue statement is used to skip the current iteration of a loop and continue with the next iteration.

for (int i = 0; i < 10; i++) { if (i == 5) { continue; // Skip the iteration when i is 5 } // Code here is executed for all other values of i }

return Statement:

• The return statement is used to exit from a method and return a value (if the method has a return type).
• It can also be used to terminate the execution of a method prematurely.

public int add(int a, int b) { int sum = a + b; return sum; // Exits the method and returns the sum }