java - 为什么这个 pojo 程序 "readline"总是返回 null？

Question

public static void main(String[] args) throws IOException {
    BufferedReader reader = new BufferedReader(new FileReader("day.txt"));
    BufferedWriter writer = new BufferedWriter(new FileWriter("day.txt"));
    System.out.println(reader.readLine());
}

day.txt 我在执行前写了一些话。如果我用 Writer 更改 System.out.println，它就不会为空。为什么？

Answer 1

当您执行 new FileWriter("day.txt");

时，您正在覆盖同一个文件

将您的代码更改为

BufferedReader reader = new BufferedReader(new FileReader("day.txt"));
BufferedWriter writer = new BufferedWriter(new FileWriter("day-new.txt"));
System.out.println(reader.readLine());