Merge pull request #696 from besok/master

#677 add pattern Trampoline.

pom.xml

@@ -147,13 +147,13 @@
         <module>event-sourcing</module>
         <module>data-transfer-object</module>
         <module>throttling</module>
-
         <module>unit-of-work</module>
         <module>partial-response</module>
         <module>eip-wire-tap</module>
         <module>eip-splitter</module>
         <module>eip-aggregator</module>
         <module>retry</module>
+		<module>trampoline</module>
     </modules>
 
     <repositories>

trampoline/.gitignore

@@ -0,0 +1,2 @@
+/target/
+.idea/

trampoline/README.md

@@ -0,0 +1,45 @@
+---
+layout: pattern
+title: Trampoline
+folder: trampoline
+permalink: /patterns/trampoline/
+categories: Behavior
+tags:
+ - Java
+ - Difficulty-Intermediate
+ - Performance
+ - Recursion
+---
+
+## Intent
+Trampoline pattern is used for implementing algorithms recursively in Java without blowing the stack 
+and to interleave the execution of functions without hard coding them together
+It is possible by representing a computation in one of 2 states : done | more 
+(completed with result, or a reference to the reminder of the computation, 
+something like the way a java.util.Supplier does).
+
+
+## Explanation
+Trampoline pattern allows to define recursive algorithms by iterative loop.
+
+
+## Applicability
+Use the Trampoline pattern when
+
+* For implementing tail recursive function. This pattern allows to switch on a stackless operation.
+* For interleaving the execution of two or more functions on the same thread.
+
+## Known uses(real world examples)
+* Trampoline refers to using reflection to avoid using inner classes, for example in event listeners. 
+The time overhead of a reflection call is traded for the space overhead of an inner class. 
+Trampolines in Java usually involve the creation of a GenericListener to pass events to an outer class.
+
+
+## Tutorials 
+* [Trampolining: a practical guide for awesome Java Developers](https://medium.com/@johnmcclean/trampolining-a-practical-guide-for-awesome-java-developers-4b657d9c3076)
+* [Trampoline in java ](http://mindprod.com/jgloss/trampoline.html)
+
+## Credits
+* [library 'cyclops-react' uses the pattern](https://github.com/aol/cyclops-react)
+
+

trampoline/pom.xml

@@ -0,0 +1,77 @@
+<?xml version="1.0"?>
+<!--
+
+    The MIT License
+    Copyright (c) 2014-2016 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.
+
+-->
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+         xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.19.0-SNAPSHOT</version>
+
+    </parent>
+    <artifactId>trampoline</artifactId>
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>1.16.18</version>
+        </dependency>
+
+
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>2.19</version>
+                <configuration>
+                    <skipTests>false</skipTests>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

trampoline/src/main/java/com/iluwatar/trampoline/Trampoline.java

@@ -0,0 +1,85 @@
+package com.iluwatar.trampoline;
+
+import java.util.stream.Stream;
+
+/**
+ * <p>Trampoline pattern allows to define recursive algorithms by iterative loop </p>
+ * <p>When get is called on the returned Trampoline, internally it will iterate calling ‘jump’
+ * on the returned Trampoline as long as the concrete instance returned is {@link #more(Trampoline)},
+ * stopping once the returned instance is {@link #done(Object)}.</p>
+ * <p>Essential we convert looping via recursion into iteration,
+ * the key enabling mechanism is the fact that {@link #more(Trampoline)} is a lazy operation.</p>
+ *
+ * @param <T> is  type for returning result.
+ */
+public interface Trampoline<T> {
+  T get();
+
+
+  /**
+   * @return next stage
+   */
+  default Trampoline<T> jump() {
+    return this;
+  }
+
+
+  default T result() {
+    return get();
+  }
+
+  /**
+   * @return true if complete
+   */
+  default boolean complete() {
+    return true;
+  }
+
+  /**
+   * Created a completed Trampoline
+   *
+   * @param result Completed result
+   * @return Completed Trampoline
+   */
+  static <T> Trampoline<T> done(final T result) {
+    return () -> result;
+  }
+
+
+  /**
+   * Create a Trampoline that has more work to do
+   *
+   * @param trampoline Next stage in Trampoline
+   * @return Trampoline with more work
+   */
+  static <T> Trampoline<T> more(final Trampoline<Trampoline<T>> trampoline) {
+    return new Trampoline<T>() {
+      @Override
+      public boolean complete() {
+        return false;
+      }
+
+      @Override
+      public Trampoline<T> jump() {
+        return trampoline.result();
+      }
+
+      @Override
+      public T get() {
+        return trampoline(this);
+      }
+
+      T trampoline(final Trampoline<T> trampoline) {
+
+        return Stream.iterate(trampoline, Trampoline::jump)
+            .filter(Trampoline::complete)
+            .findFirst()
+            .get()
+            .result();
+
+      }
+    };
+  }
+
+
+}

trampoline/src/main/java/com/iluwatar/trampoline/TrampolineApp.java

@@ -0,0 +1,58 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ * <p>
+ * 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:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * 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 lombok.extern.slf4j.Slf4j;
+
+/**
+ * <p>Trampoline pattern allows to define recursive algorithms by iterative loop </p>
+ * <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.</p>
+ */
+@Slf4j
+public class TrampolineApp {
+
+  /**
+   * Main program for showing pattern. It does loop with factorial function.
+   * */
+  public static void main(String[] args) {
+    log.info("start pattern");
+    Integer 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));
+    }
+  }
+
+}

trampoline/src/test/java/com/iluwatar/trampoline/TrampolineAppTest.java

@@ -0,0 +1,22 @@
+package com.iluwatar.trampoline;
+
+import org.junit.Test;
+
+import java.io.IOException;
+
+import static org.junit.Assert.*;
+
+
+/**
+ * Test for trampoline pattern.
+ * */
+public class TrampolineAppTest {
+
+
+  @Test
+  public void testTrampolineWithFactorialFunction() throws IOException {
+    int result = TrampolineApp.loop(10, 1).result();
+    assertEquals("Be equal", 3628800, result);
+  }
+
+}