Detailed code explanation of java using redirection method to read or write data from a file

This article mainly introduces in detail the use of redirection method to read or write data from files. It has certain reference value. Interested friends can refer to it

Using Redirection Method to read or write data from a file

1.Problem description

First generate 10,000 random numbers, one line for every ten, and put them into the file. (Use redirection method)
Use redirection method to read 10,000 numbers from the file and print out the top ten. (It is not allowed to call the sorting method)

2. The program is as follows:

2.1 Write

import java.util.Scanner;
import java.util.List;
import java.util.ArrayList;
public class A{
  
  static void to_txt(){
    for(int i=1;i<=10000;i++){
      System.out.print((int)(Math.random()*10000+1)+" ");
      if(i%10==0) System.out.println();  
    }
  }
    public static void main(String[] args){
    to_txt();
      
  }    
}

2.2 Read

import java.util.Scanner;
import java.util.List;
import java.util.ArrayList;
public class A{
  
    static void read_txt(int k){//此处参数表示打印前k项
    List<Integer> lst = new ArrayList<Integer>();
    Scanner scan = new Scanner(System.in);
    String s = scan.nextLine();
    String[] x = s.split(" ");
    lst.add(Integer.parseInt(x[0]));  
    for(int i=1;i<x.length;i++){
      int b = Integer.parseInt(x[i]);
      if(b<lst.get(lst.size()-1)){
        lst.add(b);
        continue;
      }
      for(int j=0;j<lst.size();j++){
        if(b>lst.get(j)){
          lst.add(j,b);
          break;
        }
      }
        
    }
    for(int i=0;i<k;i++){
      
      System.out.print(lst.get(i)+" ");
    }    
  }
  public static void main(String[] args){
    read_txt(10);  
  }    
}

3. Running results

3.1. Enter the console from the Java file location and enter Java file>txt file in the console to write the running results to the specified txt file (to be written file).

At this time, the running result is not displayed on the console, but written to the specified file

3.2. Enter the console at the location of the Java file and control Enter Java + file name < Specify the txt file (the file to be read)

The following figure shows the first ten items of the read data to be output.

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