java - Why does trim() not remove the trailing white spaces in this example? -

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i revising java here: http://java-success.blogspot.com.au/2012/06/core-java-coding-questions-frequently.html , came along question:

"q1. output of following code snippet?

string s = " hello "; s += " world "; s.trim( ); system.out.println(s);

a1. output be

" hello  world "

with leading , trailing spaces. expect trimmed "hello world".

so, concepts question try test?

string objects immutable , there trick in s.trim( ) line. understanding object references , unreachable objects eligible garbage collection."

can explain why trailing white spaces not removed?

the method trim() doesn't modify string, immutable. returns trimmed string, promptly ignored, leaving s unchanged. replace

s.trim( );

with

s = s.trim( );

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