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Does == on two Integers depend on the value stored?

 
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Hey Java ranchers,

I was doing a mock exam and came across this


public class Troll
{
Integer gruesomeness;
String flatness;
public static void main(String[] args)
{
Troll troll = new Troll();
Troll troll2 = new Troll();
troll.gruesomeness = 98762;
troll2.gruesomeness = 98762;
troll.flatness="flat";
troll2.flatness="flat";
System.out.println(troll.equals(troll2)); //#1
}

public boolean equals(Object arg0)
{
if (arg0 instanceof Troll)
{
Troll new_name = (Troll) arg0;
return gruesomeness==new_name.gruesomeness && new_name.flatness.equals(flatness);
}
return false;
}

public int hashCode()
{
return 0;
}
}


This prints out false at //#1 for all the values > 127. Why is that?

 
Bartender
Posts: 2700
IntelliJ IDE Opera
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Comparing Integers with == is not recommended. Use a primitive or equals.

The integer class holds a buffer for integer between the range -128 and 127 by default or the value set with the java.lang.Integer.IntegerCache.high property with a minimum of 127.

Because of the cache Integers created by autoboxing within the range are the some objects thus returning true for the == comparison. Integer obtained otherwise or not in the range, are not cached thus a new object will be created.

// And welcome to the JavaRanch. Please read our naming policy.
 
L K Kakani
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Is it the same with other Wrapper classes too?? I understand that its not suggested to use == for Wrappers, but that is inconsistent behavior.
Are we supposed to look out for such questions ?? Guess its tough to take on such ones , hopefully we don't come across these kind in the SCJP exam. Thanks for your reply..
 
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• Two instances of the wrapper objects Boolean, Byte, Character from \u0000 to \u007f and short and integer from -128 to 127 will always be == when their primitive values are same
 
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The == operator should not be used to test for "meaningful equivalence"
of objects. That a small value Integer object is cached by the JVM as a
performance optimization should not be exploited in this way. Rather,
ob1.equals(ob2) should always be used to compare objects.

Jim ... ...
 
author and jackaroo
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"java time"

Please check your private messages regarding an important administrative matter.

-Andrew
 
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@K Kakani

You could also try Integer.valueOf(...) instead of autoboxing and check the results of:
 
Wouter Oet
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Autoboxing uses the valueOf method to obtain the Wrapper object.
 
L K Kakani
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Thank you all for taking time to post replies. It was very helpful.
 
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