java-design-patterns/trampoline/src/main/java/com/iluwatar/trampoline/TrampolineApp.java

/*
 * The MIT License
 * Copyright © 2014-2019 Ilkka Seppälä
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package com.iluwatar.trampoline;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Trampoline pattern allows to define recursive algorithms by iterative loop.
 *
 * <p>It is possible to implement algorithms recursively in Java without blowing the stack
 * and to interleave the execution of functions without hard coding them together or even using
 * threads.
 */
public class TrampolineApp {

  private static final Logger log = LoggerFactory.getLogger(TrampolineApp.class);

  /**
   * Main program for showing pattern. It does loop with factorial function.
   */
  public static void main(String[] args) {
    log.info("start pattern");
    var result = loop(10, 1).result();
    log.info("result {}", result);

  }

  /**
   * Manager for pattern. Define it with a factorial function.
   */
  public static Trampoline<Integer> loop(int times, int prod) {
    if (times == 0) {
      return Trampoline.done(prod);
    } else {
      return Trampoline.more(() -> loop(times - 1, prod * times));
    }
  }

}