Why can't I replace \n in a given String?

Question

I found the question here before but somehow I can't see what I'm doing wrong. So I have a given String that looks something like this:

"Some text here\\n\\nsome more text here"

And I want to remove the linebreaks and display the Text in a TextView. I tried using String.replaceAll:

String newString = oldString.replaceAll("\\n", " ");

But that didn't change anything in the text. However, oldString.contains("\\\\n"); returns true . What am I doing wrong?

edit:

I'm sorry, I know, oldString doesn't change. The problem is that, if I print oldString and newString they're exactly the same even though it says that oldString does contain a "\\n".

This is my code:

Log.d(TAG, "contains: " + str.contains("\\n"));     
Log.d(TAG, "old: " + str);
str = str.replaceAll("\\n", " ");
Log.d(TAG, "new: " + str);

And this is what I get:

contains: true
old: Vorgang nicht möglich\n\nBitte Karte entnehmen
new: Vorgang nicht möglich\n\nBitte Karte entnehmen

UPDATE

Thanks to Shivanshu Verma , I tried str.replace("\\\\n"" "); instead of str.replaceAll("\\\\n", " "); and that works! Does anybody know, why I can't use replaceAll() here?

Answer 1

Strings in Java are immutable and as such the new string with the replacements is stored in newString, not oldString.

EDIT

I see now that your issue was not actually related to Java String immutability but rather the difference between replace() and replaceAll(). The difference between these is that replaceAll() takes in a regex as the first argument, which will then replace any matches with the second argument, whereas replace() simply takes in a CharSequence (of which String is an implementation) and will replace exact matches with the second argument.

In your case, I think your original String had the newline characters escaped:

String str = "Vorgang nicht möglich\\n\\nBitte Karte entnehmen";

which meant that the String didn't actually contain newline characters at all; it contained literally "\\n" . This would mean that:

str.replaceAll("\\n", " ");

will resolve the first argument to a regex and replace newline characters (of which there were none), and:

str.replace("\\n", " ");

will replace exact matches of "\\n" . It's also worth noting that as others have pointed out contains() also doesn't take in a regex, which is why running:

oldString.contains("\\n");

returned true.

Answer 2

Your code works perfectly fine.

This test will pass without any error:

@Test
public void testReplaceAll() {


    String newString = "line1\nline2\nline3".replaceAll("\\n", " ");

    assertThat(newString).isEqualTo("line1 line2 line3");
    assertThat(newString).doesNotContain("\\n");
}

Answer 3

try to Replace() method instead of ReplaceAll()

String newString = oldString.replace("\\n", " ");

may be it work for u

Answer 4

字符串newString = oldString.replace（“ \\ n”，“”）;