Vfrdtyky

I have the following simple piece of java code where I am trying to understand how string concatenation in java works using '+' operator.

public class Problem {



public static void main(String... args){



    String str1 = "abc";

    String str2 = "ab";

    String str3 = "c";

    String str4 = "ab" + "c";//This will use of  StringBuilder class for concatenation and return new String object

    String str5 = str2 + str3;//This will use of  StringBuilder class for concatenation and return new String object



    System.out.println(str1 == str4); // This  returns true

    System.out.println(str1 == str5); // This  returns false



}

}

str4 is the resultant of 2 string literals (ab and c) and str5 is of references to the 2 string literals (str2 and str3). In both the cases, java will be calling StringBuilder class to perform the concatenation.

And I believe it should result in creating 2 different StringBuilder objects in java heap space.

If my understanding is correct, why str1 == str4 returns true ? Can some one please help in getting this clear to me ?

Regards,
Maneesh Sharma

It depends on how the compiler and jvm will optimize this. Only if both variables are optimized to point to the same adress, the evaluation will be true. In general, using == to compare strings is not reliable. Use the 'equals' method instead.