System.lineSeparator() returns nothing

问题:

What should I see when I use the following?

System.out.println("LineSeperator1: "+System.getProperty("line.separator"));
System.out.println("LineSeperator2: "+System.lineSeparator());

I get the following back:

LineSeperator1: 

LineSeperator2: 

Is it empty? invisible? shouldn there be something like \r or \n?

I use windows 7, eclipse and jdk 1.8.

回答1:

As you expect, the line separator contains special characters such as '\r' or '\n' that denote the end of a line. However, although they would be written in Java source code with those backslash escape sequences, they do not appear that way when printed. The purpose of a line separator is to separate lines, so, for example, the output of

System.out.println("Hello"+System.lineSeparator()+"World");

is

Hello
World

rather than, say

Hello\nWorld

You can even see this in the output of your code: the output of

System.out.println("LineSeperator1: "+System.getProperty("line.separator"));

had an extra blank line before the output of the next statement, because there was a line separator from System.getProperty("line.separator") and another from the use of println.

---

If you really want to see what the escaped versions of the line separators look like, you can use escapeJava from Apache Commons. For example:

import org.apache.commons.lang3.StringEscapeUtils;

public class LineSeparators {
    public static void main(String[] args) {
        String ls1 = StringEscapeUtils.escapeJava(System.getProperty("line.separator"));
        System.out.println("LineSeperator1: "+ls1);
        String ls2 = StringEscapeUtils.escapeJava(System.lineSeparator());
        System.out.println("LineSeperator2: "+ls2);
    }
}

On my system, this outputs

LineSeparator1: \n
LineSeparator2: \n

Note that I had to run it in the same folder as the .jar file from the Apache download, compiling and running with these commands

javac -cp commons-lang3-3.4.jar LineSeparators.java
java -cp commons-lang3-3.4.jar:. LineSeparators

回答2:

Printing something afterwards will show the effect:

System.out.println("a" + System.lineSeparator() + "b");

Gives

a
b