Java: Comparing ints and Strings - Performance

Question

I have a String and an int, lets say: String str = "12345"; and int num = 12345;. What is the fastest way of seeing if they are the same, str.equals("" + num) or num == Integer.parseInt(str) (Or is there a faster way?)?

This is the source code for Integer.parseInt and String.equals

score 22 · Accepted Answer · answered Apr 13 '13 at 05:46

num == Integer.parseInt(str) is going to faster than str.equals("" + num)

str.equals("" + num) will first convert num to string which is O(n) where n being the number of digits in the number. Then it will do a string concatenation again O(n) and then finally do the string comparison. String comparison in this case will be another O(n) - n being the number of digits in the number. So in all ~3*O(n)

num == Integer.parseInt(str) will convert the string to integer which is O(n) again where n being the number of digits in the number. And then integer comparison is O(1). So just ~1*O(n)

To summarize both are O(n) - but str.equals("" + num) has a higher constant and so is slower.

That is a completely flawed and WRONG logic. O(n)+O(n) is still O(n) - you do not add those numbers as that notation only tells you about its asymptotic growth. And the rest is just as wrong. Java will usually notice that "" is an empty string so no concatination. And converting an integer to a string is, in general, quite a bit faster than the other way around as it is a known valid conversion, where as the other way around has to deal with many special cases. — ABaumstumpf, Jan 13 '21 at 11:20

score 5 · Answer 2 · answered Apr 13 '13 at 05:45

5

I think num == Integer.parseInt(str) is a better way of doing comparison. Because str.equals("" + num) this is not the ideal way how you should compare integer values and also it will create unnecessary String constant objects in the String pool (which hampers performance).

answered Apr 13 '13 at 05:45

Ankur Shanbhag

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I mean to say that integer values can be checked for equality using comparison operator '=='. – Ankur Shanbhag Apr 13 '13 at 05:48

score 1 · Answer 3 · edited Apr 17 '15 at 19:13

1

Guess you might also be able to use this to compare........

int p = 1234;
String Int = "1234";
String string = String.valueOf(p);
System.out.println(string + Int);
System.out.println(string.equals(Int));
code here

edited Apr 17 '15 at 19:13

TigerhawkT3

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answered Apr 13 '13 at 08:50

Alade Fehinti John

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How does this answer the Question? – cellepo Sep 24 '20 at 18:27

Java: Comparing ints and Strings - Performance

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