Java substring.equals versus ==

Question

Using the standard loop, I compared a substring to a string value like this:

if (str.substring(i, i+3) == "dog" ) dogcount++;

and it broke the iteration. After the first increment, no further instances of "dog" would be detected.

So I used substring.equals, and that worked:

if (str.substring(i, i+3).equals("dog")) dogcount++;

My question is, why? Just seeking better understand, thx.

Answer 1

You should use equals() instead of == to compare two strings.

s1 == s2 returns true if both strings point to the same object in memory. This is a common beginners mistake and is usually not what you want.

s1.equals(s2) returns true if both strings are physically equal (i.e. they contain the same characters).