Java Stream, File, and IO

Java Stream, File, and IO

• Java. The IO package contains almost all the classes needed to operate on inputs and outputs
  • All these stream class stream classes represent input sources and output destinations
• Java. Streams in io packages support many formats
  • Examples include basic types, objects, localized character sets, and so on
• A stream can be understood as a sequence of data
  • Input stream represents reading data from a source
  • Output stream represents writing data to a target
• Java provides strong and flexible support for I/o, making it more widely used in file transfer and network programming

Read Console Input

• Java console input is made by System.in complete

  • In order to get a character stream bound to the console, you can use System.in wraps in a BufferedReader object to create a character stream

    • Basic syntax for creating a BufferedReader:

      BufferedReader br = new BufferedReader(new  InputStreamReader(System.in));
      

      • After the BufferedReader object is created, you can use the read() method to read a character from the console or the readLine() method to read a string

Read multicharacter input from console

• To read a character from a BufferedReader object, use the read() method

  • Syntax: int read throws IOException

    • Each time the read() method is called, a character is read from the input stream and returned as an integer value

    • Return-1 when the stream ends

    • This method throws IOException

  • Example of using BufferedReader to read characters in the console

    //Use BufferedReader to read characters in the console
    
    import java.io.*;
    public class BRRead{
    public  static void main(String[] args){
    char c;
    //Use System.in Create BufferedReader
    BudderedReader br = new BufferedReader(new InputStreamReader(System.in));
    System.out.println("Enter characters, press q Key Exit");
    do{
    c=(char) br.read();
    System.out.println(c);
    }while (c!='q');
    }
    }
    

Read string from console

• Reading a string from standard input requires the reaLine() method of BufferedReader

  • Syntax: String readLine() throws IOException

    Use BufferedReader Examples of reading characters in the console
    //Use BufferedReader to read characters in the console
    impor  java.io.*;
    public class BRReadLines{
    public static void main(String[] args)  throws IOException{
    //Use System.in Create BufferedReader
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in);
    String str;
    System.out.println("Enter lines of text.");
    System.out.println("Enter 'end' to quit.");
    do{
    Str = br.readLine();
    System.out.println(str);
    }while(!str.equals("end"));                                                                                                                                         
    }
    }     
    

console output

• The output of the console is done by print() and println()

  • These methods are defined by the class PrintStream
  • System.out is a reference to this object

• PrintStream inherits the OutputStream class and implements the method write(); Write() can also be used to write operations to the console

  • PrintStream defines the simplest format for write():

    • Void write(int byteval)

      • This method writes the low octet bytes of byteval to the stream

      • Example: Use write() to output the character "A" and the following line breaks to the screen:

        import  java.io.*;
        //Demonstrate System.out.write()
        public class WriteDemo{
        public static void main(String [] args){
        int b;
        b = 'A';
        System.out.write(b);
        System.out.write('\n');
        }
        }
        

Read and write files

• A stream is defined as a data sequence
  • Input stream is used to read data from source
  • The output stream is used to write data to the target
• Two important streams, FilelnputStream and FileOutputStream

FilelnputStream

• The stream is used to read data from a file, and objects of FilelnputStream can be created with the new keyword

• There are several ways to create objects

  • You can use string-type filenames to create an input stream object to read files

    InputStream  f =new FileInputStream("C:/java/hello");
    

  • You can also use a file object to create an input stream object to read files

  • First you have to create a file object using the File() method

    File  f  = new File("C:/java/hello");
    InputStream  in = new FileInputStream(f); 
    

• public void close() throws IOException{}

  • Close this file input stream and release all system resources associated with it
  • Throw IOException Exception

• protected void finalize() throws IOException{}

  • Method Clears the connection to the file
  • Make sure to call the close method of the file input stream when it is no longer referenced
  • Throw IOException Exception

• public int read(int r) throws IOException{}

  • This method reads the specified byte of data from the InputStream object
  • Return to integer value
  • Returns the next byte of data, or -1 if it has reached the end

• public int read (byte[] r) throws IOException{}

  • This method reads r.length length bytes from the input stream
  • Returns the number of bytes read
  • Returns -1 if it is at the end of the file

• Public int available() throws IOException{}

  • Returns the number of bytes that the next method called on this input stream can read from this input stream without blocking
  • Returns an integer value

FileOutputStream