java - string trim function is not working

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

Answer

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