• Java is a

  • high level

  • robust

  • simple

  • portable

  • secure

  • stable

  • Object Oriented programming language

• Java is not a pure object-oriented language, because it supports primitive data type.

  Languages that support or have features which treat everything inside the program as an object, and doesn’t support primitive data type(like int, char, float, boolean)

• Java is platform-independent.

  JRE makes java platform independent. Once your java source code is compiled to byte code/machine independent code, that byte code will run in all devices which has JRE installed.

• Java is same as C/C++, so it is easy to learn and write program.

  Java does not support low-level programming functions like pointers.

• Java is all about classes and objects.

• Java is developed by James Ghosling, Patrick Naughton, Mike Sheridan at Sun Microsystem Inc.

• Java released its 1st working version in 1991, took 18 month to develop.

• Initially, they named it Oak, then renamed to Java as Oak was already registered for other organisation.

• Usage of Java

  • Desktop Applications
  • Web Applications
  • Mobile Operating System (ex. Android)
  • Embedded System (ex. Digital Electronics, Telecommunications, Computer Netotking, Satellite system)
  • Robotics and Games, etc (ex. manufacturing, assembling and packing, transport, surgery, weaponry, mass production of industrial goods)

• Types of Java Applications

  • Standalone Applications

    • Applications that are machine-specific, one can use them directly after installation in local machine.
    • Java developers use AWT, Swing, JavaFX to develop.
    • Examples are Media Players, Antivirus Softwares, System Settings, etc.

  • Web Applications

    • An application, that is installed and run in a powerful machine and can be accessed from remote machine by multiple users concurrently using a client application (browsers)
    • Developers around the world are using Servlets, Struts, JSP, Spring, Hibernate, etc.
    • Some realtime examples are Social media websites, -commerce websites, bank applications, etc.

  • Enterprise Applications

    • An application that improves productivity and efficiency of an organization.
    • Examples are billing systems, customer relationship management systems and supplier relationship management systems.

  • Mobile Application

• Data types defines the value type which a variable will hold.
• There are 2 categories of data types in java
  • Primitive types
  • Non-primitive types

• boolean
• char
• byte
• short
• int
• long
• float
• double

1. String

• String class is defined in java.lang package as below,

public final class String extends Object implements Serializable, Comparable<String>, CharSequence {
  // fields
  // constructors
  // methods
}

• Sequence of characters

String str0 = "India";

char[] data = { 'I', 'n', 'd', 'i', 'a' };
String str1 = new String(data);

In above example we have created 2 String objects and both are same.

• Each string literals are one object/instance of String class.
• Strings are constant, their values cannot be changed after they are created. String objects are immutable.

Methods in String class

charAt(int index)

* Returns the character located at the specific index.
* Indexing starts from 0-zero.

 ```java
 String str = "India";

 System.out.println(str.charAt(3)); // i
 ```

equalsIgnoreCase(String secondString)

• Compares the equality of two Strings, and ignores the case (upper or lower)
• Returns a boolean value (true/false)

  String str = "India";

  System.out.println(str.equalsIgnoreCase("India")); // true

1. Array