Is reflection in Java a performance killer? Run these tests to check for yourself. After compilation, just run with the command line below passing a list of any strings as command line input to args[].

IsReflectionSlow.java

import java.lang.reflect.*;

public class IsReflectionSlow {
  public static double rand() {
    return Math.random();
  }

  public static String constant() {
    return "constant";
  }

  public static String concat(String[] strings) {
    StringBuilder sb = new StringBuilder();
    for (String s : strings)
      sb.append(s).append(" ");
    return sb.toString();
  }

  public static void main(String[] args) throws Exception {
    testConstant();
    testRand();
    testConcat(args);
  }

  private static void testRand() throws Exception {
    System.out.println("***** Testing Random number generation *****");
    long startStatic = System.currentTimeMillis();
    for (int i = 0; i < 100_000_000; i++)
      rand();
    long stopStatic = System.currentTimeMillis();
    System.out.println("Static test results: " + (stopStatic - startStatic));

    Method m = IsReflectionSlow.class.getMethod("rand", new Class[0]);
    Object[] params = new Object[0];
    long startReflect = System.currentTimeMillis();
    for (int i = 0; i < 100_000_000; i++)
      m.invoke(null, params);
    long stopReflect = System.currentTimeMillis();
    System.out.println("Reflection test results: " + (stopReflect - startReflect));
  }

  private static void testConstant() throws Exception {
    System.out.println("***** Testing Constants *****");
    long startStatic = System.currentTimeMillis();
    for (int i = 0; i < 100_000_000; i++)
      constant();
    long stopStatic = System.currentTimeMillis();
    System.out.println("Static test results: " + (stopStatic - startStatic));

    Method m = IsReflectionSlow.class.getMethod("constant", new Class[0]);
    Object[] params = new Object[0];
    long startReflect = System.currentTimeMillis();
    for (int i = 0; i < 100_000_000; i++)
      m.invoke(null, params);
    long stopReflect = System.currentTimeMillis();
    System.out.println("Reflection test results: " + (stopReflect - startReflect));
  }

  private static void testConcat(String[] list) throws Exception {
    System.out.println("***** Testing Concats *****");
    long startStatic = System.currentTimeMillis();
    for (int i = 0; i < 10_000_000; i++)
      concat(list);
    long stopStatic = System.currentTimeMillis();
    System.out.println("Static test results: " + (stopStatic - startStatic));

    Method m = IsReflectionSlow.class.getMethod("concat", new Class[] {String[].class});
    long startReflect = System.currentTimeMillis();
    for (int i = 0; i < 10_000_000; i++)
      m.invoke(null, (Object) list);
    long stopReflect = System.currentTimeMillis();
    System.out.println("Reflection test results: " + (stopReflect - startReflect));
  }
}

results.txt

java IsReflectionSlow a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
***** Testing Constants *****
Static test results: 2
Reflection test results: 212
***** Testing Random number generation *****
Static test results: 2234
Reflection test results: 2697
***** Testing Concats *****
Static test results: 16341
Reflection test results: 16870