java - Experimenting with String creation -

i found interesting case while testing string creation , checking hashcode.

in first case created string using copy constructor:

public class test {      /**      * @param args      */     public static void main(string[] args) {          string s1 = new string("myteststring");          string s3 = s1.intern();          system.out.println("s1: " + system.identityhashcode(s1) + "  s3:"                 + system.identityhashcode(s3));     }   } 

output of above code is:

s1: 816115710 s3:478684581

this expected output interned string picks reference string pool whereas s1 picks reference of new object. identity hash code different.

now if create string using char array see strange behavior:

public class test {      /**      * @param args      */     public static void main(string[] args) {          char[] c1 = { 'm', 'y', 't', 'e', 's', 't', 's', 't', 'r', 'i', 'n',                 'g' };          string s5 = new string(c1);          string s6 = s5.intern();          system.out.println("s5: " + system.identityhashcode(s5) + "  s6:"                 + system.identityhashcode(s6));     }  } 

output of above code is:

s5: 816115710 s6:816115710

this unexpected output. how can interned string , new string object have same identityhashcode??

any ideas?

in first case, myteststring literal on pool before call intern, whereas in second case not string s5 put in pool directly.

if go through examples step step, happens:

• string s1 = new string("myteststring"); => use of string literal creates string myteststring in pool (let's call s0), , new string s1 created, not in pool.
• string s3 = s1.intern(); => checks if there equivalent string in pool , finds s0. s3 , s0 refer same instance (i.e. s3 == s0 true, s1 != s0).

in second example:

• string s5 = new string(c1); creates new string, not in pool
• string s6 = s5.intern(); checks if myteststring in pool can't find it, call intern creates new string reference in pool refers same string s5. s6 == s5 true.

finally can run these 2 programs confirm explanation (the second 1 prints true 3 times):

public static void main(string[] args) {     string s1 = new string("myteststring");     string s3 = s1.intern();     system.out.println("myteststring" == s1);     system.out.println(s3 == s1);     system.out.println("myteststring" == s3); }  public static void main(string[] args) {     string s1 = new string(new char[] {'m', 'y', 't', 'e', 's', 't', 's', 't', 'r', 'i', 'n', 'g'});     string s3 = s1.intern();     system.out.println("myteststring" == s3);     system.out.println("myteststring" == s1);     system.out.println(s3 == s1); }