Java输入输出

旧城等待， 2022-08-07 12:35 181阅读 0赞

# 控制台输入输出 #

## Scanner ##

[Scanner官方文档][Scanner]

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();
    }

--------------------

## 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();
             }
          }
       }
    }

--------------------

## 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();
             }
          }
       }
    }

--------------------

## 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();
             }
          }
       }
    }

--------------------

## 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");
       }    
       }
    }

--------------------

## JAVA I/O Re-direct ##

//out
    import 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!");
        }   
    }
    
    //in
    import 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());
            }
        }       
    }

--------------------

[Basic Input and Output][]

--------------------

## Character-Based I/O & Character Streams ##

![这里写图片描述][20150406131013351]

--------------------

## Byte-Based I/O & Byte Streams ##

![这里写图片描述][20150406131033007]

[Scanner]: http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html
[Basic Input and Output]: http://www3.ntu.edu.sg/home/ehchua/programming/java/j5b_io.html
[20150406131013351]: /images/20220805/306cadadd90d49b7b95d9a611e80566f.png
[20150406131033007]: /images/20220805/56c80a90dba54e6b963dc5370c938a01.png