[Java] Code that is hard to notice but terribly slow

Purpose

During the review, I came across a code that is a mixture of Integer and int. For a moment I thought that there would be no problem because it would be converted by auto boxing, but I was wondering what the performance was, so I would like to verify it.

Verification environment

Source code for verification

** 1. Pattern with a mixture of reference types and primitive types **

qiita.java


long begin = 0L;
long end = 0L;

begin = System.currentTimeMillis();

Integer sum = 0;

for(int i = 0; i < 1000000; i++) {
	sum += i;
}

end = System.currentTimeMillis();

System.out.println(end - begin + "millisecond");

** 2. Primitive type only pattern **

qiita.java


long begin = 0L;
long end = 0L;

begin = System.currentTimeMillis();

int sum = 0;

for(int i = 0; i < 1000000; i++) {
	sum += i;
}

end = System.currentTimeMillis();

System.out.println(end - begin + "millisecond");

Implementation procedure

--Perform 1,000,000 addition processing using the verification source code. The average time is calculated by measuring each three times. Round to the first decimal place.

Implementation results

** 1. Pattern with a mixture of reference types and primitive types **

--First time: 15 ms --Second time: 16 ms --Third time: 15 ms --Average: 15.33 ms

** 2. Primitive type only pattern **

--First time: 5 ms --Second time: 4 ms --Third time: 4 ms --Average: 4.33 ms

Consideration

The mixed reference and primitive patterns averaged 15.33 ms, while the primitive-only patterns averaged 4.33 ms. It can be seen that it takes about four times as long when autoboxing is working with a mixture of reference types and primitive types. It turns out that if dust accumulates, it will be a mountain, and depending on the number of data, it should not be meaninglessly auto-boxing.

See you again (^_^) Noshi

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