string trim function is not working

Question

I learned string.trim() removes leading and trailing spaces. But in my case its not working i am trying below code but output is with leading and trailing space. But my expectation is text without leading and trailing space. Here is my code.

String s = " Hello Rais ";
s += " Welcome to my World ";
s.trim( );
System.out.println(s);

Please help me

[The API in this case is very helpful.](http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#trim()) You *do* have to reassign it to the String you want - Strings are immutable. — Makoto, Feb 17 '13 at 07:48
@StephenC My code is working i was making a silli mistake. I have to assingned the return of trim function to the variable. I dont understand What are you trying to say in above comment. — Rais Alam, Feb 17 '13 at 07:53

Rohit Jain · Accepted Answer · 2013-02-17T08:01:11.727

10

You need to re-assign the result of trim back to s:

s = s.trim();

Remember, Strings in Java are immutable, so almost all the String class methods will create and return a new string, rather than modifying the string in place.

Although this is off-topic, but (as I said there almost), it's worth knowing that, exception to this rule is when creating a substring of same length, or any time a method returns the string with the same value, which will be optimized and will not create a new string, but simply return this.

String s = "Rohit";
String s2 = s.substring(0, s.length());

System.out.println(s == s2); // will print true

edited Feb 17 '13 at 08:01

answered Feb 17 '13 at 07:46

Rohit Jain

203,151
43
392
509

+1 `System.out.println(s == s2);` will be true because s and s2 has same value so for optimization they will hold same place in string pool managed by jvm. http://stackoverflow.com/questions/3801343/what-is-string-pool-in-java – Tapas Bose Feb 17 '13 at 07:57
@Rohit - thanks it was my mistake i forgot to re assign – Rais Alam Feb 17 '13 at 07:57
@Real. You're welcome :) – Rohit Jain Feb 17 '13 at 07:58
@TapasBose. Yeah right. Should have mentioned that point. Thanks :) – Rohit Jain Feb 17 '13 at 08:01
You shoud use System.out.println(s.eqauals(s2)) to check the equality. – MayurB Feb 17 '13 at 08:08
@MayurB. Is that for me? Thanks but I know that. The code is just an illustration of exception where `==` returns `true`. – Rohit Jain Feb 17 '13 at 08:09

score 6 · Answer 2 · answered Feb 17 '13 at 07:47

6

In Java Strings are immutable. So s.trim() does not modify the original string but returns a new string.

String trimmed  = s.trim();

answered Feb 17 '13 at 07:47

MoveFast

2,945
2
26
52

score 4 · Answer 3 · answered Feb 17 '13 at 07:47

4

just add s=s.trim( ); because trim returns a new string.

answered Feb 17 '13 at 07:47

Arpit

12,709
3
27
40

score 3 · Answer 4 · answered Feb 17 '13 at 07:48

3

Well..string is immutable object. so whenever you do trim(), it creates a brand new String object, which need to have a reference to access it. So do assign a reference to this trimmed String object as follows.

s = s.trim();

or

trimmedS = s.trim();

answered Feb 17 '13 at 07:48

Ahmad

2,040
4
23
33

score 3 · Answer 5 · answered Feb 17 '13 at 07:48

Understand that String in Java is immutable. Which means any operation on the String class does not change the internal string itself, but returns a new String object.

So you really need to do

s = s.trim()

which assigns the reference s to a new String object that has its trailing and leading spaces removed.

score 2 · Answer 6 · answered Feb 17 '13 at 07:49

trim function returns a copy of the original string by trimming the white spaces so you need to store the newly returned string like s = s.trim()

From the javadocs of String#trim()

trim

public String trim()
Returns a copy of the string, with leading and trailing whitespace omitted.

string trim function is not working

6 Answers6

Linked

Related