1. I/O Basics Java does provide strong, flexible support for I/O related to files and networks. Java’s console based interaction is limited since in real time application java accepts inputs from AWT,Swing etc. Java performs I/O operation through streams Stream is an abstraction either produces or consumes information. Streams linked to a physical devices in same manner irrespective of physical devices Same I/O classes and methods are used for disk files,console,etc.

2. Streams Java defines two types of streams Byte Stream and Character stream. Byte streams provide a convenient means for handling input and output of bytes. Byte streams are used when reading or writing binary data. Character streams provide a convenient means for handling input and output of characters. They use Unicode and, therefore, can be internationalized. At the lowest level, all I/O are byte-oriented. The character-based streams simply provide a convenient and efficient means for handling characters. Java implements streams within class hierarchies defined in the java.io package.

3. Byte Stream Byte streams are defined by using two class hierarchies. At the top are two abstract classes : InputStream and OutputStream. Each of these abstract classes has several concrete subclasses, that handle the differences between various devices, such as disk files, network connections, and even memory buffers.

5. The abstract classes InputStream and OutputStream define several key methods that the other stream classes implement. Two of the most important are read() and write(), which, respectively, read and write bytes of data. Both methods are declared as abstract inside InputStream and OutputStream. They are overridden by derived stream classes.

6. Character Stream Character streams are defined by using two class hierarchies. At the top are two abstract classes, Reader and Writer. The abstract classes Reader and Writer define several key methods that the other stream classes implement. Two of the most important methods are read() and write(), which read and write characters of data, respectively. These methods are overridden by derived stream classes.

7. Predefined Streams The java.lang package defines a class called System, which encapsulates several aspects of the runtime environment. System contains three predefined stream variables, in,out, and err. These fields are declared as public and static within System. System.out refers to the standard output stream. By default, this is the console. System.in refers to standard input, which is the keyboard by default. System.err refers to the standard error stream, which also is the console by default.

8. Reading Console Input Console input is done by System.in this is an object of InputStream (Byte Stream) To obtain a character-based stream that is attached to the console, wrap System.in in a BufferedReader object. BuffereredReader supports a buffered input stream. Its most commonly used constructor is shown here: BufferedReader(Reader inputReader) inputReader is the stream that is linked to the instance of BufferedReader that is being created. Reader is an abstract class. One of its concrete subclasses is InputStreamReader, which converts bytes to characters. To obtain an InputStreamReader object that is linked to System.in, use the following constructor: InputStreamReader(InputStream inputStream) Because System.in refers to an object of type InputStream, it can be used for inputStream.

9. BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br is a character-based stream that is linked to the console through System.in.

10. Reading Characters The method read() is used to read a character from a BufferedReader Each time that read() is called, it reads a character from the input stream and returns it as an integer value. read() returns –1 when the end of the stream is encountered. read() can throw an IOException. To read String use br.ReadLine(); BufferedReadApplication.java

11. java.io.*; class BRRead { public static void main(String args[]) throws IOException { char c; BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); System.out.println("Enter 'q' to quit."); do { c = (char) br.read(); System.out.println(c); } while(c != 'q'); } Enter 'q' to quit. 123abcq 1 2 3 a b c q

12. Console output is most easily accomplished with print( ) and println( ), described earlier. These methods are defined by the class PrintStream (which is the type of the object referenced by System.out). Even though System.out is a byte stream, using it for simple program output is still acceptable. However, using a PrintWriter will make your real-world applications easier to internationalize.

13. Reading and Writing Files In Java, all files are byte-oriented, and Java provides methods to read and write bytes from and to a file. Java wraps a byte-oriented file stream within a character-based object. Two of the most often-used stream classes are FileInputStream and FileOutputStream, which create byte streams linked to files. To open a file, create an object of one of these classes, specifying the name of the file as an argument to the constructor. FileInputStream(String fileName) throws FileNotFoundException FileOutputStream(String fileName) throws FileNotFoundException

14. To read from a file,create the object of FileInputStream and use the method read() Each time that it is called, it reads a single byte from the file and returns the byte as an integer value. read() returns –1 when the end of the file is encountered. It can throw an IOException. While creating an input stream, if the file does not exist, then FileNotFoundException is thrown.

15. 1.Write an application that reads and counts the number of words,special characters, digits and lines of a text file.the output should be written in to another file.

16. To write in to the file create the object of FileOutputStream FileOutputStream fout; fout = new FileOutputStream(fileName, true); Creating file in append mode Ref :FileApplications.java

17. String Handling String is sequence of characters In java String is an immutable object Immutable :- Strings within objects of type String are unchangeable means that the contents of the String instance cannot be changed after it has been created. However, a variable declared as a String reference can be changed to point at some other String object at any time. For those cases in which a modifiable string is desired, there is a companion class to String called StringBuffer, whose objects contain strings that can be modified after they are created.

18. String constructors Following default constructor creates an instance of string with no character in it. String s = new String(); To create a String initialized by an array of characters, use the constructor shown here: String(char chars[]) char chars[]={'a','b','c'}; String s =new String(chars); Specify a subrange of a character array as an initializer using the following constructor: String(char chars[],int startIndex,int numChars) –startIndex specifies the index at which the subrange begins, and numChars specifies the number of characters to use. char chars[] = {'a','b','c','d','e','f'}; String s = new String(chars,2,3); This initializes s with the characters cde. String(String strObj) initializes string with the value of another string

19. String APIs String s1="Hello"; s1.length(); gives the length of string int age =25; String s2=“I am“+age+”years young”;

20. When Java converts data into its string representation during concatenation, it does so by calling one of the overloaded versions of the string conversion method valueOf() defined by String. valueOf() is overloaded for all the simple types and for type Object. For the simple types, valueOf( ) returns a string that contains the human-readable equivalent of the value with which it is called. Every class implements toString() because it is defined by Object. For the classes we create we want to override toString() and provide our own string representations. The toString() method has this general form: String toString() To implement toString(), simply return a String object that contains the human-readable string that appropriately describes an object of your class. Ref:ToStringAppln.java

21. StringBuffer StringBuffer is a peer class of String that provides much of the functionality of strings. String represents fixed-length, immutable character sequences. In contrast, StringBuffer represents growable and writeable character sequences. StringBuffer may have characters and substrings inserted in the middle or appended to the end. StringBuffer will automatically grow to make room for such additions Java uses both classes heavily, but many programmers deal only with String and let Java manipulate StringBuffers behind the scenes by using the overloaded + operator.

22. Write a program that implements string editor

23. Java.lang java.lang is automatically imported into all programs. It is Java's most widely used package. Contains classes and interfaces that are fundamental to virtually all of Java programming. This package contains lots of classes and three interfaces. Clonable,Runnable and Comparable

24. Java uses simple types, such as int and char, for performance reasons. These data types are not part of the object hierarchy. They are passed by value to methods and cannot be directly passed by reference. There is no way for two methods to refer to the same instance of an int. There are situations where we need objects than primitive types to store the value.In such a situation to store a simple type in one of these classes, we need to wrap the simple type in a class. To address the above situation java provides wrapper classes.These classes encapsulate, or wrap, the simple types within a class.

25. The abstract class Number defines a superclass that is implemented by the classes that wrap the numeric types byte, short, int, long, float, and double. has abstract methods that return the value of Number the object in each of the different number formats. That is, doubleValue( ) returns the value as a double, floatValue( ) returns the value as a float, and so on.

26. Number Double and Float Byte, Short, Integer, and Long Character Boolean