Thread.setPriority（） 工作不正常？

问：

我只是在玩线程。我正在多线程程序中读取两个文本文件 A.txt 和 B.txt。 我正在做的是，我为从 A.txt 读取数据的线程分配了更高的优先级。 但这并没有产生影响。 首先读取 .txt 文件或出现异常情况。 此外，还发生了异常。 这里有人请帮帮我。

无效 main（）

package introtothreading;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.lang.Thread;
import java.util.logging.Level;
import java.util.logging.Logger;

public class IntroToThreading {
public static void main(String[] args) { 
FileReaderA fa = new FileReaderA();
FileReaderB fb = new FileReaderB();
Thread t4 =  new Thread(fa);
Thread t5 =  new Thread(fb);
t4.setPriority(Thread.MAX_PRIORITY);
t5.setPriority(Thread.MIN_PRIORITY);
t5.start();
t4.start();
}   
}

FileReaderA

 public class FileReaderA  implements Runnable
 {
File f = new File("D:/a.txt") ;
FileReader fr ;
BufferedReader br ;
public FileReaderA()
{
    try {
        fr = new FileReader(f);  
        br  =  new BufferedReader(fr);
    } catch (FileNotFoundException ex) {
        Logger.getLogger(FileReaderA.class.getName()).log(Level.SEVERE, null, ex);
    }
}

@Override
public void run() {
    try {       
        String s;
        s = br.readLine();
        do
        {
        System.out.println(s);
        s = br.readLine();
        }
        while(! s.equals(""));
        //To change body of generated methods, choose Tools | Templates.
    } catch (IOException ex) {
        System.out.println("IO Exception..");
    }
   }    
   }

文件阅读器B

 public class FileReaderB implements Runnable
 {


 File f = new File("D:/b.txt") ;
 FileReader fr ;
 BufferedReader br ;
 public FileReaderB()
 {
    try {
        fr = new FileReader(f);  
        br  =  new BufferedReader(fr);
    } catch (FileNotFoundException ex) {
        Logger.getLogger(FileReaderB.class.getName()).log(Level.SEVERE, null, ex);
    }
 }

 @Override
 public void run() {
    try {       
        String s1;
        s1 = br.readLine();
        do
        {
        System.out.println(s1);
        s1 = br.readLine();
        }
        while(!s1.equals(" "));
        //To change body of generated methods, choose Tools | Templates.
     } catch (IOException ex) {
        System.out.println("IO Exception..");
    }
 }    
 }

输出

 run:
 1-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 Exception in thread "Thread-4" java.lang.NullPointerException
at introtothreading.FileReaderB.run(FileReaderB.java:39)
at java.lang.Thread.run(Thread.java:744)
2-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
5-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
1-bbbbbbbbbbbbbbbbbbbbbbbb
2-bbbbbbbbbbbbbbbbbbbbbbbb
3-bbbbbbbbbbbbbbbbbbbbbb
4-bbbbbbbbbbbbbb
5-bbbbbbbbbbbbbbbbbbbbbbbbbbbb
6-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
7-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
8-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
6-bbb
7-bbbbbbbbbbbbbb
8-bbbbb
9-bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
BUILD SUCCESSFUL (total time: 10 seconds)


**output2**


 1-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 1-bbbbbbbbbbbbbbbbbbbbbbbb
 2-bbbbbbbbbbbbbbbbbbbbbbbb
 3-bbbbbbbbbbbbbbbbbbbbbb
 4-bbbbbbbbbbbbbb
 5-bbbbbbbbbbbbbbbbbbbbbbbbbbbb
 6-bbb
 7-bbbbbbbbbbbbbb
 8-bbbbb
 9-bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
 2-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 3-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 4-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 5-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 6-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 7-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 8-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 Exception in thread "Thread-4" java.lang.NullPointerException
at introtothreading.FileReaderB.run(FileReaderB.java:39)
at java.lang.Thread.run(Thread.java:744)

和我的

a.txt 文件包含

1-啊啊

2-啊啊

3-啊

4-啊

5-啊

6-啊啊

7-啊啊

8-啊啊

b.txt 文件包含

1-bbbbbbbb

2-bbbbbbbb

3-bbbbbbbbbb

4-bbbbbbbbbb

5-bbbbbbbb

6-桶

7-bbbbbbbbbb

8-BBBB桶

9-bbbbbb