What will be the output of following quiz on Integer Comparison ?
Answer
When we assign a literal number to Integer, compiler adds Integer.valueOf for the literal.
For example,
Integer i1= -128 becomes Integer i1= Integer.valueOf(-128)
In valueOf implementation, by default integers -128 to 127 are cached and the cached instance is returned for the integer.
Therefore i1==i2 returns true as they are referring to same cached instance.
However, 128 is not cached, so i3==i4 returns false.
The default high value until which integers are cached is 127. So, values from -128 till 127 is cached.
The high value up to which Integers are cached can be updated using the system property java.lang.Integer.IntegerCache.high
Correct answer is “true,false”
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The result depends on the config, with the default config, the answer is correct
That was interesting, thanks for posting! I don’t compare objects with the equal sign, only with the {Objectname}.equals() function. That doesn’t use hacks like this 🙂
Integer pool, one byte.
“The high value up to which Integers are cached can be updated using the system property java.lang.Integer.IntegerCache.high”
This is true starting as of JDK 7. JDK 5 and 6 threshold values are hard coded.