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Semester 3: Advanced Java Programming
Java basics - OOP, data types, variables, arrays, control statements, classes, inheritance, exceptions
Java basics
Object-Oriented Programming (OOP)
Java is an object-oriented programming language that follows the principles of OOP which include encapsulation, inheritance, polymorphism, and abstraction. OOP helps in organizing code into classes and objects, making it easier to manage and reuse.
Data Types
Java has two categories of data types: primitive data types and reference data types. Primitive data types include int, char, double, boolean, etc. Reference data types refer to objects and arrays.
Variables
Variables in Java are used to store data. They must be declared with a specific data type before they can be used. The syntax for declaring a variable is: dataType variableName; Example: int age;.
Arrays
An array in Java is a container that holds a fixed number of values of a single type. The array index starts at zero. Arrays can be single-dimensional or multi-dimensional.
Control Statements
Control statements in Java are used to control the flow of execution. They include decision-making statements (if, switch) and looping statements (for, while, do-while).
Classes
A class in Java is a blueprint for creating objects. It encapsulates data for the object and methods to manipulate that data. The basic structure includes class declaration, fields, and methods.
Inheritance
Inheritance is a feature in Java where a new class can inherit properties and methods from an existing class. This promotes code reusability and establishes a hierarchical relationship between classes.
Exceptions
Exceptions in Java are events that disrupt the normal flow of the program. They can be handled using try-catch blocks. Java provides built-in exceptions, and users can also define their own.
String handling - constructors, length, operations, IO classes, streams
String handling
Constructors
In Java, strings are objects created from the String class. Constructors can be used to create string objects in multiple ways. The most common constructors are: 1. String(): Creates an empty string object. 2. String(String str): Creates a string object initialized to the contents of the specified string. 3. String(char[] value): Creates a string object initialized to the contents of the character array.
Length
The length method is used to determine the number of characters in a string. It returns an integer value. For example, using the method str.length() will yield the length of the string str.
Operations
Strings in Java provide a variety of operations such as concatenation, comparison, substring creation, and searching. Common methods include: 1. concat(String str): Concatenates the specified string to the end of the current string. 2. equals(Object obj): Compares two strings for content equality. 3. substring(int beginIndex, int endIndex): Returns a new string that is a substring of the original string.
IO Classes
Input and Output classes in Java handle string data when reading from and writing to different sources. The java.io package provides classes like FileReader, BufferedReader, PrintWriter, and FileWriter that work with string data.
Streams
Java provides the concept of streams for handling input and output. String data can be manipulated using byte and character streams. Character streams use classes like FileReader and FileWriter, while byte streams use FileInputStream and FileOutputStream. For string manipulation, character streams are preferred as they handle text data more efficiently.
Applet class - architecture, skeleton, display, parameters
Applet Class
Architecture
The applet class in Java is part of the AWT (Abstract Window Toolkit) and serves as a base class for creating applets. Applets are small Java programs that can be embedded in web pages and run in a sandboxed environment for security purposes. The architecture generally consists of several components including the applet lifecycle methods such as init, start, stop, and destroy. The applet interacts with the browser and handles graphics and user inputs through a graphical user interface.
Skeleton
The skeleton of an applet consists of the necessary class declaration that extends the Applet class or the JApplet class, overriding lifecycle methods. The basic structure includes import statements, class declaration, and method definitions. For instance, the init method is used for initialization tasks, while the paint method is crucial for rendering graphics.
Display
The display aspect of applets is handled through the paint method, which is invoked when the applet needs to be rendered or re-rendered. Graphics objects are utilized within this method to draw on the applet's context. The display can be customized using shapes, colors, and images, allowing for an interactive user experience.
Parameters
Applets can receive parameters from the HTML page in which they are embedded. These parameters can be accessed through the getParameter method. Common use cases include setting the size of the applet, changing colors, or passing configuration options. This flexibility allows for dynamic behavior depending on the environment or user preferences.
Swing GUI - components, containers, MVC, simple applications
Swing GUI
Components
Swing GUI components are objects that allow user interaction. Common components include buttons, labels, text fields, checkboxes, and lists. Each component is an instance of the Java Swing library classes and is designed to perform specific tasks. Components can also have properties which define their appearance and behavior.
Containers
Swing uses containers to hold components. The most common container is JFrame, which represents a window. Other important containers include JPanel, which can hold smaller sets of components, and JScrollPane, which provides a scrollable view of another component. Containers can be nested to create complex layouts.
MVC Architecture
Swing follows the Model-View-Controller (MVC) design pattern. The model represents the data, the view is the user interface, and the controller responds to user inputs. This separation allows for easier management of complex applications by decoupling the GUI from the underlying data and logic.
Creating Simple Applications
To create a simple Swing application, you typically start by creating a JFrame object. You then add components like buttons and text fields to the frame. Event listeners are added to components to handle user interactions, which lets the application respond to events. An example might be a simple calculator that takes input from text fields and displays results when a button is pressed.
Java Beans - advantages, API, examples
Java Beans
Introduction to Java Beans
Java Beans are reusable software components that can be manipulated in a builder tool. They follow specific conventions allowing them to be easily integrated into various applications.
Advantages of Java Beans
1. Reusability: Java Beans promote the reuse of software components, saving time and effort. 2. Introspection: Frameworks can analyze beans at runtime, allowing for manipulation and configuration. 3. Customization: Properties and methods can be customized for specific applications. 4. Event Handling: Java Beans support event listeners, enabling communication between objects.
Java Beans API
The Java Beans API provides the necessary classes and interfaces that facilitate the creation and use of beans. This includes the classes in the `java.beans` package which offer tools for bean management.
Example of a Java Bean
A simple Java Bean might include private properties, public getter and setter methods, and a no-argument constructor. Example: java public class Person { private String name; private int age; public Person() {} public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }
Use Cases of Java Beans
Commonly used in web applications, enterprise applications (EJBs), and for creating UI components in Java frameworks like Swing and JavaFX.
Servlets - life cycle, API, cookies, session tracking
Servlets
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The init method is called once when the servlet is loaded into memory. It initializes the servlet and sets up any required resources.
The service method is called to process requests from the client. It handles requests and responses, typically using doGet or doPost methods.
The destroy method is called once when the servlet is taken out of service. It cleans up resources and performs any necessary shutdown operations.
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Servlet API provides the interfaces and classes for writing servlets. key components include HttpServlet, ServletRequest, ServletResponse, etc.
Is an abstract class that extends GenericServlet and implements the HttpServlet API.
A protocol-independent servlet class that can handle requests and responses.
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Cookies are small pieces of data stored on the client side, used for tracking and managing sessions.
Cookies can be created using the Cookie class and added to the response using response.addCookie(cookie).
Cookies are read from the request using request.getCookies() method.
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Session tracking is a mechanism to maintain state and data across multiple requests from the same user.
Common methods include cookies, URL rewriting, and using HttpSession for session management.
HttpSession is a Java interface that provides methods for session management, including setAttribute, getAttribute, and invalidate.
Network programming - URLs, sockets, RMI
Network programming - URLs, sockets, RMI
URLs
Uniform Resource Locators (URLs) are the addresses used to access resources on the internet. A URL consists of several components, including the scheme (http, https, ftp), the host (domain name or IP address), the port (optional), the path to the resource, and query parameters (optional). Properly understanding URLs is essential for web development and network programming.
Sockets
A socket is an endpoint for sending or receiving data across a computer network. It allows for communication between two devices using a client-server architecture. In Java, the Socket class facilitates creating a client socket while the ServerSocket class is used for the server side. Sockets use protocols like TCP for reliable communication and UDP for faster, but less reliable, communication.
Remote Method Invocation (RMI)
Java RMI enables invoking methods of remote objects in a networked environment. It allows Java programs to communicate with each other, regardless of where they are located. RMI abstracts the complexity of network communication and provides a straightforward API for creating distributed applications. Key components of RMI include the remote interface, remote object implementation, and stub/skeleton generation for communication.
Database connectivity - SQL, JDBC, scrollable result sets
Database connectivity - SQL, JDBC, scrollable result sets
Introduction to Database Connectivity
Database connectivity refers to the means of connecting to a database from an application. It involves establishing a connection, executing queries, and handling results. Common methods for database connectivity include using SQL with JDBC.
Understanding SQL
SQL stands for Structured Query Language. It is the standard language used to communicate with relational databases. SQL encompasses various operations like data retrieval (SELECT), data manipulation (INSERT, UPDATE, DELETE), and database schema creation/management (CREATE, ALTER, DROP).
JDBC Overview
JDBC, or Java Database Connectivity, is an API that allows Java applications to interact with a database. It provides a set of interfaces and classes to connect to databases, execute SQL statements, and retrieve results. JDBC supports different databases through the use of drivers.
Types of JDBC Drivers
There are four types of JDBC drivers: Type 1 - JDBC-ODBC Bridge Driver, Type 2 - Native-API Driver, Type 3 - Network Protocol Driver, and Type 4 - Thin Driver. Each has its own characteristics and performance implications, with Type 4 being the most commonly used for Java applications.
Scrollable Result Sets
A scrollable result set allows the application to navigate through the results of a query in any direction (forward or backward). This is beneficial for applications that require advanced navigation capabilities over the retrieved data. JDBC provides methods to create scrollable result sets.
Implementing JDBC for Scrollable Result Sets
To implement JDBC for scrollable result sets, developers typically use the Statement or PreparedStatement interface with appropriate parameters. For instance, using Connection.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY) allows for scrolling through the results.
Best Practices for Database Connectivity
Some best practices include: using connection pooling to optimize performance, closing connections properly to prevent memory leaks, handling exceptions effectively, using prepared statements to guard against SQL injection, and regularly monitoring and optimizing database queries.
