我必须使用Java中的多线程技术从文件F1和F2中读取内容并将其移至新文件(f3)。我面临的问题是,当我在方法中使用同步时,我无法获得答案,但是当我不同步方法时,则能够获得答案。
下面是带有同步方法的代码,该方法仅打印一个文件的内容:
package com.company;
import java.io.*;
import java.io.FileReader;
public class FileMerge{
public static void main(String[] args) throws IOException, InterruptedException {
WriteToFile pc = new WriteToFile();
//Create a Thread1 to read the content of file 1
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
pc.file1();
} catch (InterruptedException | IOException e) {
System.out.println(e);
}
}
});
// Create Thread 2 to read the content of file 2
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
try {
pc.file2();
} catch (InterruptedException | IOException e) {
System.out.println(e);
}
}
});
//Start the Thread
t1.start();
t2.start();
t1.join();
t2.join();
}
public static class WriteToFile{
PrintWriter pw = new PrintWriter("C:/Users/paras.jain/Desktop/des.txt");
public WriteToFile() throws FileNotFoundException {
}
public synchronized void file1() throws InterruptedException, IOException {
// BufferedReader object for file1.txt
BufferedReader br = new BufferedReader(new FileReader("C:\\Users\\paras.jain\\Desktop\\f.txt"));
String line = br.readLine();
//System.out.println("----------" + line);
// loop to copy each line of
// file1.txt to file3.txt
while (line != null) {
pw.println(line);
line = br.readLine();
}
br.close();
pw.close();
}
public synchronized void file2() throws InterruptedException, IOException {
BufferedReader br1 = new BufferedReader(new FileReader("C:/Users/paras.jain/Desktop/f2.txt"));
String line2 = br1.readLine();
//System.out.println("----------" + line2);
// loop to copy each line of
// file2.txt to file3.txt
while (line2 != null) {
pw.println(line2);
line2 = br1.readLine();
//System.out.println("----------" + line2);
}
br1.close();
pw.close();
}
}
}
以上代码的输出为:
File 1 line 1
File 1 line 2
File 1 line 3
当我运行代码没有同步方法时,我得到以下输出:
File 1 line 1
File 1 line 2
File 2 line 1
File 2 line 2
File 1 line 3
File 2 line 3
为什么输出差异?我如何在同步方法的帮助下获得第二个输出?
当file1()
和file2()
方法同步时,其中一个必须先完成,而另一个才能运行。
仅在要写入同一文件时才需要控制并发性。当您要读取两个单独的文件时,不需要同步,因此仅在要写入第三个文件时才需要同步执行。像这样的代码。