Performance of Set and Get using Reflection

Question

Does setting and getting an object attribute using reflection (java.lang.reflect.Field get and set functions) rather than calling the set and get of the object itself, result in any significant performance differences?

Answer 1

Yes, the benchmark is easy to write in 15 minutes.

Generated code is better, even if you cache the reflective accessors, I have tried it.

Here it is under Java 7 64 bits:

import java.lang.reflect.Field;

class Data {
   public double _value;
   public double getValue()               { return _value; }
   public void   setValue( double value ) { _value = value; }
}

public class Reflect {
   public static final int LOOP_COUNT = 100_000_000;
   public static void main( String[] args ) throws Throwable {
      Data d = new Data();
      long start = System.currentTimeMillis();
      for( int i = 0; i < LOOP_COUNT; ++i ) {
         d.setValue( i );
      }
      System.err.println( System.currentTimeMillis() - start );
      Field field = Data.class.getDeclaredField( "_value" );
      start = System.currentTimeMillis();
      for( int i = 0; i < LOOP_COUNT; ++i ) {
         field.set( d, new Double( i ));
      }
      System.err.println( System.currentTimeMillis() - start );

      field.setAccessible( true ); // Optimization
      start = System.currentTimeMillis();
      for( int i = 0; i < LOOP_COUNT; ++i ) {
         field.set( d, new Double( i ));
      }
      System.err.println( System.currentTimeMillis() - start );
   }
}

Result:

20
37381
1677

Ratio is near 1870 w/o accessible flag set. Setting it makes ratio drop to 83.