Java Integer equals vs

Question

As of Java 1 5  you can pretty much interchange Integer with int in many situations   However  I found a potential defect in my code that surprised me a bit   The following code   Integer cdiCt        Integer cdsCt            if  cdiCt    null  amp  amp  cdsCt    null  amp  amp  cdiCt    cdsCt      mismatch   true    appeared to be incorrectly setting mismatch when the values were equal  although I can t determine under what circumstances  I set a breakpoint in Eclipse and saw that the Integer values were both 137  and I inspected the boolean expression and it said it was false  but when I stepped over it  it was setting mismatch to true   Changing the conditional to   if  cdiCt    null  amp  amp  cdsCt    null  amp  amp   cdiCt equals cdsCt     fixed the problem   Can anyone shed some light on why this happened  So far  I have only seen the behavior on my localhost on my own PC  In this particular case  the code successfully made it past about 20 comparisons  but failed on 2  The problem was consistently reproducible   If it is a prevalent problem  it should be causing errors on our other environments  dev and test   but so far  no one has reported the problem after hundreds of tests executing this code snippet   Is it still not legitimate to use    to compare two Integer values   In addition to all the fine answers below  the following stackoverflow link has quite a bit of additional information  It actually would have answered my original question  but because I didn t mention autoboxing in my question  it didn t show up in the selected suggestions   Why can t the compiler JVM just make autoboxing    just work

User · Accepted Answer

The JVM is caching Integer values  Hence the comparison with    only works for numbers between -128 and 127  Refer   Immutable Objects  2F Wrapper Class Caching

User · Answer

always compare the memory location or object references of the values  equals method always compare the values  But equals also indirectly uses the      operator to compare the values   Integer uses Integer cache to store the values from -128 to  127  If    operator is used to check for any values between -128 to 127 then it returns true  for other than these values it returns false    Refer the  link  for some additional info

User · Answer

As well for correctness of using    you can just unbox one of compared Integer values before doing    comparison  like   if   firstInteger intValue      secondInteger         The second will be auto unboxed  of course you have to check for nulls first

User · Answer

Besides these given great answers  What I have learned is that      NEVER compare objects with    unless you intend to be comparing them   by their references

User · Answer

You can t compare two Integer with a simple    they re objects so most of the time references won t be the same   There is a trick  with Integer between -128 and 127  references will be the same as autoboxing uses Integer valueOf   which caches small integers      If the value p being boxed is true  false  a byte  a char in the range  u0000 to  u007f  or an int or short number between -128 and 127  then let r1 and r2 be the results of any two boxing conversions of p  It is always the case that r1    r2      Resources     JLS - Boxing   On the same topic     autoboxing vs manual boxing java

User · Answer

The issue is that your two Integer objects are just that  objects  They do not match because you are comparing your two object references  not the values within  Obviously  equals is overridden to provide a value comparison as opposed to an object reference comparison

User · Answer

Integer refers to the reference  that is  when comparing references you re comparing if they point to the same object  not value   Hence  the issue you re seeing   The reason it works so well with plain int types is that it unboxes the value contained by the Integer   May I add that if you re doing what you re doing  why have the if statement to begin with   mismatch     cdiCt    null  amp  amp  cdsCt    null  amp  amp   cdiCt equals  cdsCt

[java] Java: Integer equals vs. ==

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