我用BufferedReader读文件,然后用BufferedWriter写入文件运行后出现空指针异常java.lang.NullPointerException,请问是什么问题呀?谢谢各位大神。
import java.io.*;
public class TestDemo{
public static void main(String args[]){
BufferedReader br = null;
BufferedWriter bw = null;
FileReader fr = null;
FileWriter fw = null;
try{
fr = new FileReader("F:/src/f.txt");
br = new BufferedReader(fr);
fw = new FileWriter("F:/src/t.txt");
bw = new BufferedWriter(fw);
while(true){
String str = br.readLine();
if(str.equals(null)){
break;
}
bw.write(str);
bw.newLine();
bw.flush();
}
}
catch(Exception e){
System.out.println(e);
}
finally{
try{
br.close();
fr.close();
bw.close();
fw.close();
}
catch(Exception e){
System.out.println(e);
}
}
}
}