java,l = inputStream.readLine())!= null背后的原理逻辑

Question

我是java新手,无法理解下面示例中显示的一些基本原则.有人可以在下面的代码的上下文中解释l = inputStream.readLine())!= null的含义吗？非常感谢您的帮助.

import java.io.FileReader;
import java.io.FileWriter;
import java.io.BufferedReader;
import java.io.PrintWriter;
import java.io.IOException;

public class CopyLines {
public static void main(String[] args) throws IOException {

    BufferedReader inputStream = null;
    PrintWriter outputStream = null;

    try {
        inputStream = new BufferedReader(new FileReader("xanadu.txt"));
        outputStream = new PrintWriter(new FileWriter("characteroutput.txt"));

        String l;
        while ((l = inputStream.readLine()) != null) {
            outputStream.println(l);
        }
    } finally {
        if (inputStream != null) {
            inputStream.close();
        }
        if (outputStream != null) {
            outputStream.close();
        }
    }
}
}

Answer 1

这段代码

while ((l = inputStream.readLine()) != null) {
    outputStream.println(l);
}

是等价的

l = inputStream.readLine();
while (l != null)
{

    l = inputStream.readLine();
}

因此,当读者无法读取新行时,它会返回null,从而打破循环.