java - confused about String vs Integer -

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• weird integer boxing in java 9 answers

i have question comparing string , integer objects...

a. comparing string references:

    string string1 = "hi";     system.out.printf("%s \n", string1);     string originalstring = string1;     system.out.printf("%-9s %-9s  %b \n", string1, originalstring, originalstring == string1);     system.out.println();      string1 += " there";     originalstring += " there";     system.out.printf("%-9s %-9s  %b \n", string1, originalstring, originalstring.equals(string1));     system.out.printf("%-9s %-9s  %b \n", string1, originalstring, originalstring == string1); 

produced output:

    hi      hi        hi         true       hi there  hi there   true      hi there  hi there   false  

here, last line compares addresses , expected gives false. ok far ;)

b. comparing integer references:

    integer integer1 = 10;     system.out.printf("%d \n", integer1);     integer originalinteger = integer1;     system.out.printf("%d %d  %b \n", integer1, originalinteger, originalinteger == integer1);     system.out.println();      integer1++;     originalinteger++;     system.out.printf("%d %d  %b \n", integer1, originalinteger, originalinteger == integer1); 

produced output:

    10      10 10  true       11 11  true  

by time last line printed out, both 'integer1' , 'originalinteger' referencing different objects... nevertheless

   originalinteger == integer1   --> true  ??? 

does imply not addresses of objects the contents of objects compared? in other words, because, type wrappers, values 'unboxed' before being compared?

so, resume:

originalstring == string1     --> false originalinteger == integer1     --> true 

i don't understand why originalinteger == integer1 --> true

thank you

the == compares reference of object (the "address", put it), understood (correctly) string example.

when apply ++ operator integer, in fact outboxing primitive int, incrementing it, , autoboxing integer, theoretically, different object there. however, integer class plays "dirty" trick here (read: neat optimization). values 127 (inclusive), java keeps cache of integers , returns same object whenever value autoboxed. so, in fact, getting same object, originalinteger == integer1 return true. if repeat example larger integer, let's 500, you'd false expect.