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Last Updated: May 18, 2017
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· mufid
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Box / Unboxing vs. Encapsulation: Java's `Map<Something, Integer>`

Problem: I want a map that store integer as its value. Now i
have two approaches:

  1. Use anything as key and Integer (non-primitive integer) as value, or
  2. Use anything as key and a class that contains int (primitive integer) as value.

Which should i use? The first solution seems pretty neat, nothing
to do. Just instatiate new Integer and done. At the other hand,
performance wise, it will do unnecessary boxing/unboxing if
not properly handled. Remember that we only able to use primitive
integer to do calculation and primitive integer to store value
to the map.

The Test

Benchmark withBoxing = new Benchmark() {
  public void run() {
    Map<String, Integer> a = new HashMap<String, Integer>();

    // Simulate much boxing
    for (int i = 0; i < MAX; i++) {
      a.put("" + i, i);
    }

    // Simulate much unboxing
    for (int i = 0; i < MAX; i++) {
      // A hack so that JVM does not optimize this code.
      hack += a.get("" + i); 
      hack = hack % 1000;
    }
  }
};
Benchmark encapsulate = new Benchmark() {
  public void run() {
    Map<String, EncapsulatedInteger> a = new HashMap<String, EncapsulatedInteger>();

    // No boxing/unboxing, but new class
    for (int i = 0; i < MAX; i++) {
      a.put("" + i, new EncapsulatedInteger(i));
    }

    for (int i = 0; i < MAX; i++) {
      // A hack so that JVM does not optimize this code.
      hack += a.get("" + i).v; 
      hack = hack % 1000;
    }
  }
};

The run command

javac MapPerf.java; java -Xmx1024m -cp . MapPerf

The Result

$ javac MapPerf.java; java -Xmx1024m -cp . MapPerf
Boxing/unboxing: 10973 ms
Encapsulation: 7036 ms

Summary

With Integer as value, the routine is 50% slower because of unnecessary
boxing/unboxing

Github

https://github.com/mufid/boxing-unboxing-java-perf

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