Java输入输出

控制台输入输出

Scanner

Scanner官方文档

public static void main(String[] args)   {         List<Integer> arry=new ArrayList<Integer> ();        Scanner sc = new Scanner(System.in);        while(sc.hasNextLine())        {            String str=sc.nextLine();            Scanner scc=new Scanner(str);            while(scc.hasNextInt())            {            temp=scc.nextInt();            arry.add(temp);            }            scc.close();            for (int ss : arry) {                System.out.print(ss+" ");            }            arry.clear();            System.out.println();        }        sc.close();}

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Byte Streams

Java byte streams are used to perform input and output of 8-bit bytes. Though there are many classes related to byte streams but the most frequently used classes are , FileInputStream and FileOutputStream.

import java.io.*;public class CopyFile {   public static void main(String args[]) throws IOException   {      FileInputStream in = null;      FileOutputStream out = null;      try {         in = new FileInputStream("input.txt");         out = new FileOutputStream("output.txt");         int c;         while ((c = in.read()) != -1) {            out.write(c);         }      }finally {         if (in != null) {            in.close();         }         if (out != null) {            out.close();         }      }   }}

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Character Streams

Java Byte streams are used to perform input and output of 8-bit bytes, where as Java Character streams are used to perform input and output for 16-bit unicode. Though there are many classes related to character streams but the most frequently used classes are , FileReader and FileWriter.. Though internally FileReader uses FileInputStream and FileWriter uses FileOutputStream but here major difference is that FileReader reads two bytes at a time and FileWriter writes two bytes at a time.

import java.io.*;public class CopyFile {   public static void main(String args[]) throws IOException   {      FileReader in = null;      FileWriter out = null;      try {         in = new FileReader("input.txt");         out = new FileWriter("output.txt");         int c;         while ((c = in.read()) != -1) {            out.write(c);         }      }finally {         if (in != null) {            in.close();         }         if (out != null) {            out.close();         }      }   }}

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Standard Streams

All the programming languages provide support for standard I/O where user’s program can take input from a keyboard and then produce output on the computer screen. If you are aware if C or C++ programming languages, then you must be aware of three standard devices STDIN, STDOUT and STDERR. Similar way Java provides following three standard streams

Standard Input: This is used to feed the data to user’s program and usually a keyboard is used as standard input stream and represented as System.in.

Standard Output: This is used to output the data produced by the user’s program and usually a computer screen is used to standard output stream and represented as System.out.

Standard Error: This is used to output the error data produced by the user’s program and usually a computer screen is used to standard error stream and represented as System.err.

import java.io.*;public class ReadConsole {   public static void main(String args[]) throws IOException   {      InputStreamReader cin = null;      try {         cin = new InputStreamReader(System.in);         System.out.println("Enter characters, 'q' to quit.");         char c;         do {            c = (char) cin.read();            System.out.print(c);         } while(c != 'q');      }finally {         if (cin != null) {            cin.close();         }      }   }}

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FileInputStream

This stream is used for reading data from the files. Objects can be created using the keyword new and there are several types of constructors available.

import java.io.*;public class fileStreamTest{   public static void main(String args[]){   try{      byte bWrite [] = {11,21,3,40,5};      OutputStream os = new FileOutputStream("test.txt");      for(int x=0; x < bWrite.length ; x++){         os.write( bWrite[x] ); // writes the bytes      }      os.close();      InputStream is = new FileInputStream("test.txt");      int size = is.available();      for(int i=0; i< size; i++){         System.out.print((char)is.read() + "  ");      }      is.close();   }catch(IOException e){      System.out.print("Exception");   }       }}

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JAVA I/O Re-direct

//outimport java.io.FileOutputStream;import java.io.PrintStream;public class Test {    public static void main(String[] args) throws Exception    {               PrintStream ps=new PrintStream(new    FileOutputStream("work"));        System.setOut(ps);        System.out.println("Hello World!");    }   }//inimport java.io.FileInputStream;import java.util.Scanner;public class Test {    public static void main(String[] args) throws Exception    {        FileInputStream fis=new FileInputStream("work");        System.setIn(fis);              Scanner sc=new Scanner(System.in);        while(sc.hasNextLine())        {            System.out.println(sc.nextLine());        }    }       }

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Basic Input and Output

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Character-Based I/O & Character Streams

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Byte-Based I/O & Byte Streams