如果字符串是在同一个程序中构建的，我建议使用它：

If the string was constructed in the same program, I would recommend using this:

String newline = System.getProperty("line.separator");
boolean hasNewline = word.contains(newline);

但是如果你打算使用\ n，这个驱动程序说明了该怎么做：

But if you are specced to use \n, this driver illustrates what to do:

class NewLineTest {
    public static void main(String[] args) {
        String hasNewline = "this has a newline\n.";
        String noNewline = "this doesn't";

        System.out.println(hasNewline.contains("\n"));
        System.out.println(hasNewline.contains("\\n"));
        System.out.println(noNewline.contains("\n"));
        System.out.println(noNewline.contains("\\n"));

    }

}

导致

true
false
false
false

在回复你的评论时：

class NewLineTest {
    public static void main(String[] args) {
        String word = "test\n.";
        System.out.println(word.length());
        System.out.println(word);
        word = word.replace("\n","\n ");
        System.out.println(word.length());
        System.out.println(word);

    }

}

结果

6
test
.
7
test
 .