Core Java

Java Evolution
Java History
Java Features
Benefits of Java over C and C++
How Java works
The Java Programming Language
The Java Platform
Java Development Kit
HARDWARE AND SOFTWARE REQUIREMENTS
Disadvantages of Java
Overview of Java Language
Developing the Java Application
Comments in Java Code
Defining a Class
The main Method
Using Classes and Objects
Java Program Structure
Java Tokens
Constant, Variable and Datatype
Variables
Declaring Variables
Rules on Variable Names
Variable Types
Primitive Data Types
Constants
Operator and Expression
Expressions and Operators
Operator Precedence
Integer Operators
Relational Integer Operators
Floating point Operators
Relational Floating-Point Operators
String Operator
Assignment Operators
Arithmetic assignment operations
Conversions
Casts
Boolean expressions and operations
Logical operators
Bitwise operations
The complement operator
Decision making, Branching and Looping
Flow control with if and else
The if statement
The else statement
Switch statements
for, while, and do-while statements
The for statement
The while statement
The do-while statement
Using break and continue
The break statement
The continue statement
Class Object and Method
Introduction to Classes
The Benefit of Classes
Defining Classes
Class using constructor
Object
Declaring an Object
Instantiating an Object
Initializing an Object
Referencing an Object's Variables
Calling an Object's Methods
Creating a Class
The Class Declaration
The Class Body
Constructors for Classes
Implementing Methods
The Method Body
A Method's Name
Example of the Math class
The Applet Package
Array and String
Arrays
Java arrays
Object arrays
Strings
String Concatenation
Inheritance
Introduction
Creating Subclasses
Member Variables In Subclass Inherit?
Hiding Member Variables
Methods In Subclass Inherit?
Overriding Methods
Methods a Subclass Cannot Override
Methods a Subclass Must Override
The Benefits of Inheritance
Interfaces
Interfaces and Classes
Implementing and Using Interfaces
Implementing Multiple Interfaces
Creating and Extending Interfaces
Methods Inside Interfaces
Extending Interfaces
Package
Introduction
Declaring Packages
Importing Packages
Creating Our Own Packages
The Java Language Package
The Java I/O Package
The Java Utility Package
The Java Networking Package
The Applet Package
The Abstract Window Toolkit Packages
Multithreading
Introduction
Thread
Thread Attributes
Thread State
Thread Group
Methods that Operate on the Group
Access Restriction Methods
The notifyAll() and wait() Methods
Frequently used Method
Exception Handling
Introduction
What Is an Exception?
If Exceptions than?
The exception handling technique
Some Terminology
Throw an Exception
Throw, try, and catch Blocks
Multiple catch Blocks
The finally Clause
The Throwable Class
Types of Exceptions
Different List of Exception
Built-In Exceptions
Applet
Introduction
How Applets and Applications Are Different
Limitation of Applet
The Applet class
Major Applet Activities
The life cycle of a Web page applet
Including an Applet on a Web Page
Essential HTML to launch an applet and pass it parameters
Launching an applet in an HTML document
A sample applet that receives a parameter
Posting a Web page that launches a custom applet
Managing Input/Output Files in Java
Introduction
Streams
Input Streams
The Abstract Class InputStream
The File class
The FileDialog class
Low-level and high-level stream classes
The FileOutputStream class
The FileInputStream class
The DataOutputStream class
The DataInputStream class
The ObjectOutputStream class
The ObjectInputStream class

Array and String


Strings

A sequence of character data is called a string and is implemented in the Java environment by the String class (a member of the java.lang package). The character-counting program uses Strings in two different places. The first is in the definition of the main() method:
String[] args
 
This code explicitly declares an array, named args, that contains String objects. The empty brackets indicate that the length of the array is unknown at compilation time because the array is passed in at runtime.
 
The second use of Strings in the example program is these two uses of literal strings
(a string of characters between double quotation marks " and "):
 
"Input has "
. . .
" chars."
 
The compiler implicitly allocates a String object when it encounters a literal string. So, the program implicitly allocates two String objects one for each of the two literal strings shown previously.
String String[] arrayOfStrings = new String[10];
 
The elements in this array are reference types, that is, each element contains a reference to a String object.
 
 
At this point, enough memory has been allocated to contain the String references, but no memory has been allocated for the Strings themselves. If we attempted to access one of arrayOfStrings elements at this point, we would get a NullPointerException because the array is empty and contains no Strings and no String objects.
 
We have to allocate the actual String objects separately:
for (int i = 0; i < arrayOfStrings.length; i ++)
{
arrayOfStrings[i] = new String("Hello " + i);
 
objects are immutable--that is, they cannot be changed once they've been created. The java.lang package provides a different class, StringBuffer, which we can use to create and manipulate character data on the fly.