java - Why Comparison Of two Integer using == sometimes works and sometimes not? -

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• why 128==128 return false 127==127 return true when converting integer wrappers? 6 answers
• why equal operator works integer value until 128 number? [duplicate] 7 answers

i know comparing reference while i'm using == not idea did not understand why happening.

integer a=100; integer b=100; integer c=500; integer d=500; system.out.println(a == b); //true system.out.println(a.equals(b)); //true system.out.println(c == d); //false system.out.println(c.equals(d)); //true 

the java language specification says wrapper objects @ least -128 127 cached , reused integer.valueof(), implicitly used autoboxing.