Stream, file, IO

Read console input characters

Java The console input of is provided by System.in complete .

To get a character stream bound to the console , You can take System.in Packed in a BufferedReader Object to create a character stream .

 public static void main(String args[]) throws IOException
   {
      char c;
      //  Use  System.in  establish  BufferedReader 
      BufferedReader br = new BufferedReader(new 
                         InputStreamReader(System.in));
      System.out.println(" The input character ,  Press down  'q'  Key to exit .");
      //  Read character 
      do {
         c = (char) br.read();
         System.out.println(c);
      } while(c != 'q');
   }

//  Use  BufferedReader  Read characters on the console 
import java.io.*;
public class BRReadLines {
   public static void main(String args[]) throws IOException
   {
      //  Use  System.in  establish  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 controlled by print() and println() complete . These methods are all made up of classes PrintStream Definition ,System.out Is a reference to the class object .

PrintStream Inherited OutputStream class

Read and write files

Java flow (Stream)、 file (File) and IO_w3cschool

Scanner class

java.util.Scanner yes Java5 New features , We can go through Scanner Class to get user input .

adopt Scanner Class next() And nextLine() Method to get the input string , Understand the difference between the two methods

import java.util.Scanner; 

public class ScannerDemo {  
    public static void main(String[] args) {  
        Scanner scan = new Scanner(System.in); 
		//  Receive data from keyboard   

		//next Method receive string 
        System.out.println("next Mode reception ：");
        //  Judge whether there is any input 
        if(scan.hasNext()){   
        	String str1 = scan.next();
        	System.out.println(" The data entered is ："+str1);  
        }  

    }  
} 

Output results

  The character after the space is not output

import java.util.Scanner; 

public class ScannerDemo {  
    public static void main(String[] args) {  
        Scanner scan = new Scanner(System.in); 
		//  Receive data from keyboard   

		//nextLine Method receive string 
        System.out.println("nextLine Mode reception ：");
        //  Judge whether there is any input 
        if(scan.hasNextLine()){   
        	String str2 = scan.nextLine();
        	System.out.println(" The data entered is ："+str2);  
        }  

    }  
} 

 

next() And nextLine() difference

next():

• 1、 You must read valid characters before you can end the input .
• 2、 Whitespace encountered before entering valid characters for ,next() Method will automatically remove it .
• 3、 The space entered after a valid character is used as a separator or terminator only after it is entered .
• next() Cannot get string with space .

nextLine()：

• 1、 With Enter End of character , in other words nextLine() Method returns all the characters before enter .
• 2、 Can get blank .

If you want to enter int or float Data of type , stay Scanner Class is also supported , But it's better to use it before entering hasNextXxx() Method validation , Reuse nextXxx() To read ：

import java.util.Scanner;  

public class ScannerDemo {  
    public static void main(String[] args) {  
        Scanner scan = new Scanner(System.in);  
		//  Receive data from keyboard   
        int i = 0 ;  
        float f = 0.0f ;  
        System.out.print(" Input integer ：");  
        if(scan.hasNextInt()){                 
			//  Judge whether the input is an integer   
            i = scan.nextInt() ;                
			//  Receive integer   
            System.out.println(" Integer data ：" + i) ;  
        }else{                                 
			//  Enter the wrong information   
            System.out.println(" Input is not an integer ！") ;  
        }  
        System.out.print(" Input decimal ：");  
        if(scan.hasNextFloat()){              
			//  Determine whether the input is a decimal   
            f = scan.nextFloat() ;             
			//  Receive decimal   
            System.out.println(" Fractional data ：" + f) ;  
        }else{                                
			//  Enter the wrong information   
            System.out.println(" The input is not a decimal ！") ;  
        }  
    }  
}