Steps:

·      Register the driver class

The forName() method of Class class is used to register the driver class. This method is used to dynamically load the driver class.

    Class.forName("oracle.jdbc.driver.OracleDriver");  

·       Create the connection object

The getConnection() method of DriverManager class is used to establish connection with the database.

Connection con=DriverManager.getConnection( "jdbc:oracle:thin:@localhost:1521:xe","system","password");  

·      Create the Statement object

The createStatement() method of Connection interface is used to create statement. The object of statement is responsible to execute queries with the database.

Statement stmt=con.createStatement();  

·      Execute the query

The executeQuery() method of Statement interface is used to execute queries to the database. This method returns the object of ResultSet that can be used to get all the records of a table.

ResultSet rs=stmt.executeQuery("select * from emp");  

while(rs.next())

{  

System.out.println(rs.getInt(1)+" "+rs.getString(2));  

}  

5) Close the connection object

By closing connection object statement and ResultSet will be closed automatically. The close() method of Connection interface is used to close the connection.

con.close();  

 A Java package is a set of classes which are grouped together. This grouping helps to organize Java classes and interfaces classes with the same name.

• A package provides a unique namespace for the types it contains.
• Classes in the same package can access each other’s package-access members.

Creating package

package world;

public class HelloWorld {

  public static void main(String[] args) {

    System.out.println(“Hello World”);

  }

}

Calling package

import world.*; 

import world.moon;

PATH: maintains a list of directories. The OS searches the PATH entries for executable programs, such as Java Compiler (javac) and Java Runtime (java).

CLASSPATH: maintain a list of directories (containing many Java class files) and JAR files (a single-file archive of Java classes). The Java Compiler and Java Runtime searches the CLASSPATH entries for Java classes referenced in your program.

 

• Class and object

A class is a blueprint that describes characteristics and functions of entity.. For example, the class Dog would consist of traits shared by all dogs. A class is collection of the properties and methods are called members. Object is an instance of class.

Data abstraction: – it is a process that provides only essential features by hiding its background details. A data abstraction is a simple view of an object that includes required features and hides the unnecessary details.

•  Data abstraction & Data encapsulation –

it is a process that provides only essential features by hiding its background details. A data abstraction is a simple view of an object that includes required features and hides the unnecessary details. it is a mechanism of bundling the data, and the functions that use them and data abstraction is a mechanism of exposing only the interfaces and hiding the implementation details from the user.

• Applet vs Application program

Java Application:

• A java application is a stand-alone program. This means it can be run by itself.
• It cannot access from web browser.
• It is run by JVM.
• It can access on local machine on which program is reside.

Applet

• Applet cannot run as independent program.
• Applet program can run from within a web browser or similar java enabled application such as an applet viewer
• Java applets are included in HTML pages using <applet> tag.
• Applet communicates with server only.
• Applets are not allowed to read or write to files on the local system.

 Package in Java is a mechanism to encapsulate a group of classes, sub packages and interfaces.

Advantages of using a Package in Java

• Reusability - While developing a project in java, we often feel that there are few things that we are writing again and again in our code. Using packages, you can create such things in form of classes inside a package and whenever you need to perform that same task, just import that package and use the class.

• Better Organization - Again, in large java projects where we have several hundreds of classes, it is always required to group the similar types of classes in a meaningful package name so that you can organize your project better and when you need something you can quickly locate it and use it, which improves the efficiency.

• Name Conflicts - We can define two classes with the same name in different packages so to avoid name collision, we can use packages.

There are 4 types of java access modifiers :

• private - The private access modifier is accessible only within class.

• default - If you don't use any modifier, it is treated as default bydefault. The default modifier is accessible only within package.

• protected - The protected access modifier is accessible within package and outside the package but through inheritance only.

• public - The public access modifier is accessible everywhere. It has the widest scope among all other modifiers.

 

• A static method belongs to the class rather than the object of a class.
• A static method can be accessed directly by the class name and doesn’t need any object.
• A static method can access static data member and can change the value of it.
• A static method cannot refer to "this" or "super" keywords in anyway.

In core Java program, execution starts from main method when you type java main-class-name, JVM search for public static void main(String args[ ]) method in that class and if it doesn't find that method it throws error NoSuchMethodError:main and terminates.

 Layout Manager: The Layout managers enable us to control the way in which visual components are arranged in the GUI forms by determining the size and position of components within the containers.

Java – Flow Layout

Flow layout is the default layout, which means if you don’t set any layout in your code then layout would be set to Flow by default. Flow layout puts components (such as text fields, buttons, labels etc) in a row, if horizontal space is not enough to hold all components then Flow layout adds them in a next row and so on.

Example: Here is the image of a Frame where eight buttons have been added to a Frame under Flow layout. As you can see buttons 7 & 8 are in second row because first six buttons consumed all horizontal space.

Points to Note:

• All rows in Flow layout are center aligned by default. As you can see in the above image that buttons 7 & 8 are in center. However we can set the alignment to left or right, we will learn about it later in this post.
• The default horizontal and vertical gap between components is 5 pixels.
• By default the components Orientation is left to right, which means the components would be added from left to right, however we can change it to right to left as well, we will see that later in this post.

Simple Flow Layout Example

The image shown above is the output of this code. Here we are adding 8 buttons to a Frame and layout is being set to FlowLayout.

import java.awt.*;
public class FlowLayoutDemo extends Frame{
    // constructor
    public FlowLayoutDemo(String title)
    {   
        /* It would create the Frame by calling
         * the constructor of Frame class.
         */
        super(title);    
        
        //Setting up Flow Layout
        setLayout(new FlowLayout());
        
        //Creating a button and adding it to the frame
        Button b1 = new Button("Button:1");
        add(b1);
        
        /* Adding other components to the Frame
         */
        Button b2 = new Button("Button:2");
        add(b2);
        
        Button b3 = new Button("Button:3");
        add(b3);
        
        Button b4 = new Button("Button:4");
        add(b4);
        
        Button b5 = new Button("Button:5");
        add(b5);
        
        Button b6 = new Button("Button:6");
        add(b6);
        
        Button b7 = new Button("Button:7");
        add(b7);
        
        Button b8 = new Button("Button:8");
        add(b8);
    }
    public static void main(String[] args)
    {   FlowLayoutDemo screen = 
            new FlowLayoutDemo("Flow Layout - Beginnersbook.com");
        screen.setSize(400,150);
        screen.setVisible(true);
    }
}

Flow Layout where Orientation is right to left

The default Orientation for flow layout is left to right, however we can set it to right to left if want.

import java.awt.*;
public class FlowLayoutDemo extends Frame{
    // constructor
    public FlowLayoutDemo(String title)
    {   
        /* It would create the Frame by calling
         * the constructor of Frame class.
         */
        super(title);    
        
        //Setting up Flow Layout
        setLayout(new FlowLayout());
        
        //Creating a button and adding it to the frame
        Button b1 = new Button("Button:1");
        add(b1);
        
        /* Adding other components to the Frame
         */
        Button b2 = new Button("Button:2");
        add(b2);
        
        Button b3 = new Button("Button:3");
        add(b3);
        
        Button b4 = new Button("Button:4");
        add(b4);
        
        Button b5 = new Button("Button:5");
        add(b5);
        
        Button b6 = new Button("Button:6");
        add(b6);
        
        Button b7 = new Button("Button:7");
        add(b7);
        
        Button b8 = new Button("Button:8");
        add(b8);
        /* This would set the Orientation to 
         *  RightToLeft
         */
        setComponentOrientation(
                ComponentOrientation.RIGHT_TO_LEFT);
        
    }
    public static void main(String[] args)
    {   FlowLayoutDemo screen = 
            new FlowLayoutDemo("Flow Layout - Beginnersbook.com");
        screen.setSize(400,150);
        screen.setVisible(true);
    }
}

 Exception: When an error occurs within a method, the method creates an object and hands it off to the runtime system. The object, called an exception object, contains information about the error, including its type and the state of the program when the error occurred. Creating an exception object and handing it to the runtime system is called throwing an exception.

Types of Exception in Java with Examples

Built-in exceptions are the exceptions which are available in Java libraries. These exceptions are suitable to explain certain error situations. Below is the list of important built-in exceptions in Java. 
 

1. ArithmeticException 
   It is thrown when an exceptional condition has occurred in an arithmetic operation.
2. ArrayIndexOutOfBoundsException 
   It is thrown to indicate that an array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of the array.
3. ClassNotFoundException 
   This Exception is raised when we try to access a class whose definition is not found
4. FileNotFoundException 
   This Exception is raised when a file is not accessible or does not open.
5. IOException 
   It is thrown when an input-output operation failed or interrupted
6. InterruptedException 
   It is thrown when a thread is waiting , sleeping , or doing some processing , and it is interrupted.
7. NoSuchFieldException 
   It is thrown when a class does not contain the field (or variable) specified
8. NoSuchMethodException 
   It is thrown when accessing a method which is not found.
9. NullPointerException 
   This exception is raised when referring to the members of a null object. Null represents nothing
10. NumberFormatException 
    This exception is raised when a method could not convert a string into a numeric format.
11. RuntimeException 
    This represents any exception which occurs during runtime.
12. StringIndexOutOfBoundsException 
    It is thrown by String class methods to indicate that an index is either negative or greater than the size of the string

Exception handling

Exception handling ensures that the flow of the program doesn’t break when an exception occurs. For example, if a program has bunch of statements and an exception occurs mid way after executing certain statements then the statements after the exception will not execute and the program will terminate abruptly.

class Main {
  public static void main(String[] args) {

    try {

      // code that generate exception
      int divideByZero = 5 / 0;
      System.out.println("Rest of code in try block");
    }
    
    catch (ArithmeticException e) {
      System.out.println("ArithmeticException => " + e.getMessage());
    }
  }
}

Output

ArithmeticException => / by zero

 Polymorphism: Polymorphism is considered one of the important features of Object-Oriented Programming. Polymorphism allows us to perform a single action in different ways. In other words, polymorphism allows you to define one interface and have multiple implementations. The word “poly” means many and “morphs” means forms, So it means many forms.

A person at the same time can have different characteristic. Like a man at the same time is a father, a husband, an employee. So the same person posses different behavior in different situations. This is called polymorphism.

Polymorphism in java programming

In Java polymorphism is mainly divided into two types:

• Compile time Polymorphism
• Runtime Polymorphism

1. Compile-time polymorphism: It is also known as static polymorphism. This type of polymorphism is achieved by function overloading or operator overloading. But Java doesn’t support the Operator Overloading.

Method Overloading: When there are multiple functions with same name but different parameters then these functions are said to be overloaded. Functions can be overloaded by change in number of arguments or/and change in type of arguments.

2. Runtime Polymorphism: It is also known as Dynamic Method Dispatch. It is a process in which a function call to the overridden method is resolved at Runtime. This type of polymorphism is achieved by Method Overriding.

Method Overriding , on the other hand, occurs when a derived class has a definition for one of the member functions of the base class. That base function is said to be overridden

 Java final keyword

In Java, the final keyword is used to denote constants. It can be used with variables, methods, and classes.

Once any entity (variable, method or class) is declared final, it can be assigned only once. That is,

• the final variable cannot be reinitialized with another value
• the final method cannot be overridden
• the final class cannot be extended

---

1. Java final Variable

In Java, we cannot change the value of a final variable. For example,

class Main {
  public static void main(String[] args) {

    // create a final variable
    final int AGE = 32;

    // try to change the final variable
    AGE = 45;
    System.out.println("Age: " + AGE);
  }
}

In the above program, we have created a final variable named age. And we have tried to change the value of the final variable.

When we run the program, we will get a compilation error with the following message.

cannot assign a value to final variable AGE
    AGE = 45;
    ^

 The prime reason behind creation of Java was to bring portability and security feature into a computer language. Beside these two major features, there were many other features that played an important role in moulding out the final form of this outstanding language. Those features are :

1) Simple

Java is easy to learn and its syntax is quite simple, clean and easy to understand.The confusing and ambiguous concepts of C++ are either left out in Java or they have been re-implemented in a cleaner way.

Eg : Pointers and Operator Overloading are not there in java but were an important part of C++.

2) Object Oriented

In java, everything is an object which has some data and behaviour. Java can be easily extended as it is based on Object Model. Following are some basic concept of OOP's.

1. Object

2. Class

3. Inheritance

4. Polymorphism

5. Abstraction

6. Encapsulation

3) Robust

Java makes an effort to eliminate error prone codes by emphasizing mainly on compile time error checking and runtime checking. But the main areas which Java improved were Memory Management and mishandled Exceptions by introducing automatic Garbage Collector and Exception Handling.

4) Platform Independent

Unlike other programming languages such as C, C++ etc which are compiled into platform specific machines. Java is guaranteed to be write-once, run-anywhere language.

On compilation Java program is compiled into bytecode. This bytecode is platform independent and can be run on any machine, plus this bytecode format also provide security. Any machine with Java Runtime Environment can run Java Programs.

5) Secure

When it comes to security, Java is always the first choice. With java secure features it enable us to develop virus free, temper free system. Java program always runs in Java runtime environment with almost null interaction with system OS, hence it is more secure.

6) Multi Threading

Java multithreading feature makes it possible to write program that can do many tasks simultaneously. Benefit of multithreading is that it utilizes same memory and other resources to execute multiple threads at the same time, like While typing, grammatical errors are checked along.

7) Architectural Neutral

Compiler generates bytecodes, which have nothing to do with a particular computer architecture, hence a Java program is easy to intrepret on any machine.

8) Portable

Java Byte code can be carried to any platform. No implementation dependent features. Everything related to storage is predefined, example: size of primitive data types

9) High Performance

Java is an interpreted language, so it will never be as fast as a compiled language like C or C++. But, Java enables high performance with the use of just-in-time compiler.

10) Distributed

Java is also a distributed language. Programs can be designed to run on computer networks. Java has a special class library for communicating using TCP/IP protocols. Creating network connections is very much easy in Java as compared to C/C++.

New Features of JAVA 8

Below mentioned are some of the core upgrades done as a part of Java 8 release. Just go through them quickly, we will explore them in details later.

• Enhanced Productivity by providing Optional Classes feature, Lamda Expressions, Streams etc.

• Ease of Use

• Improved Polyglot programming. A Polyglot is a program or script, written in a form which is valid in multiple programming languages and it performs the same operations in multiple programming languages. So Java now supports such type of programming technique.

• Improved Security and performance.

New Features of JAVA 11

Java 11 is a recommended LTS version of Java that includes various important features. These features includes new and upgrades in existing topic. Just go through them quickly, we will explore them in details later.

• includes support for Unicode 10.0.0

• The HTTP Client has been standarized

• Lazy Allocation of Compiler Threads

• Updated Locale Data to Unicode CLDR v33

• JEP 331 Low-Overhead Heap Profiling

• JEP 181 Nest-Based Access Control

• Added Brainpool EC Support (RFC 5639)

• Enhanced KeyStore Mechanisms

• JEP 332 Transport Layer Security (TLS) 1.3

• JEP 330 Launch Single-File Source-Code Programs