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Posted on 2004-04-28
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Last Modified: 2011-09-20
hi expert..
say:
int i = 500;
int j = 600;

String s1 = "Sad";
String s1 = "Bad";

if( i == j ) or if( s1.equals( s2) ) more faster???

please explan why?
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Question by:Dishan Fernando
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by:CEHJ
CEHJ earned 25 total points
ID: 10937801
int will be faster - as it's a leaner operation. Why are you interested?
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by:mmuruganandam
mmuruganandam earned 75 total points
ID: 10937806
primitive data type will be faster always.

i == j is a simple computation....

String is an object and there is a method invocation will cost bit more time

So always the primitive data type operations are faster than the object comparison.


Regards,
Muruga
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by:CEHJ
ID: 10937815
Hang on - they're actually likely to be virtually identical
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by:searlas
searlas earned 25 total points
ID: 10937846
You're comparing an operator to a method invocation.  It doesn't matter that you're calling 'equals' on the string, it could be any method.

I'll go out on a limb here and say it's highly likely that ALL operators in Java are faster than method invocations.

i.e.  i == j, i << j, i + j, i * j, i / j.....

Faster than.
obj.method(param);

Method invocation implies stack manipulation, looking up method entry point etc etc...
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mmuruganandam earned 75 total points
ID: 10937852
I am strongly saying that primitive data types are much faster than anything.  
Object are always slower than the primitive data type operations.


Here is the proof...

      public static void main(String[] args)
      {
            String a = "hello";
            String b = "whatis";
            
            int aa = 500;
            int bb = 600;
            
            long start = System.currentTimeMillis();
            for (int i = 0; i < 1000000; i++)
            {
                  if (aa == bb)
                  {
                  }
            }
            System.out.println("Integer comparison... time taken: " + (System.currentTimeMillis() - start));
            
            start = System.currentTimeMillis();
            for (int i = 0; i < 1000000; i++)
            {
                  if (a.equals(b))
                  {
                  }
            }
            System.out.println("String comparison... time taken: " + (System.currentTimeMillis() - start));
      }
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Expert Comment

by:searlas
ID: 10937861
(before someone points it out... I'm not including str1 + obj as an operator as that implies calls to toString... therefore has implicit method invocation...)
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by:CEHJ
ID: 10937874
I was thinking that the VM might have a way of knowing that a String taken from the constant pool is not the same as another one taken from the constant pool, but on inspection, it looks like this is not the case. The only real way to ascertain this sort of thing is by profiling it. 'Opinions' are not very useful
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by:mmuruganandam
ID: 10937886
>> String b = "whatis";

String b = "whati";

with same length data with different string will increase the time taken...
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Expert Comment

by:mmuruganandam
ID: 10937901
that's great :-)
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Expert Comment

by:CEHJ
ID: 10937940
Along the lines of what i was getting at

         String a = "hello";
         String b = "hello";

will take quite a bit less time and

            String a = "haaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
            String b = "haaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";

won't be any slower
         
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