Test Compilation Speed : ScriptEngines « Development « Java Tutorial

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2. Development
3. ScriptEngines

import javax.script.Compilable;
import javax.script.CompiledScript;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;

public class TestCompilationSpeed {
  final static int MAX_ITERATIONS = 10000;

  public static void main(String[] args) throws Exception {
    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("JavaScript");

    String fact = "function fact (n){if (n == 0)return 1; else return n*fact (n-1);};";

    long time = System.currentTimeMillis();
    for (int i = 0; i < MAX_ITERATIONS; i++)
      engine.eval(fact);
    System.out.println(System.currentTimeMillis() - time);

    Compilable compilable = null;
    if (engine instanceof Compilable) {
      compilable = (Compilable) engine;
      CompiledScript script = compilable.compile(fact);

      time = System.currentTimeMillis();
      for (int i = 0; i < MAX_ITERATIONS; i++)
        script.eval();
      System.out.println(System.currentTimeMillis() - time);
    }
  }
}