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‎trampoline/README.md

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@@ -24,15 +24,17 @@ and to interleave the execution of functions without hard coding them together o
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Use the Trampoline pattern when
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* For implementing tail recursive function. This pattern allows to switch on a stackless operation.
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* For to interleaving the execution of two or more functions on the same thread.
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* For interleaving the execution of two or more functions on the same thread.
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## Known uses(real world examples)
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* Trampoline refers to using reflection to avoid using inner classes, for example in event listeners.
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The time overhead of a reflection call is traded for the space overhead of an inner class.
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Trampolines in Java usually involve the creation of a GenericListener to pass events to an outer class.
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## Credits
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* [Trampolining: a practical guide for awesome Java Developers](https://medium.com/@johnmcclean/trampolining-a-practical-guide-for-awesome-java-developers-4b657d9c3076)
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* [Trampoline in java ](http://mindprod.com/jgloss/trampoline.html)
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* [cyclops-react](https://github.com/aol/cyclops-react)
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‎trampoline/src/main/java/com/iluwatar/trampoline/App.java

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

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package com.iluwatar.trampoline;
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import java.util.stream.Stream;
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/**When get is called on the returned Trampoline, internally it will iterate calling ‘jump’
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on the returned Trampoline as long as the concrete instance returned is More,
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stopping once the returned instance is Done. Essential we convert looping via recursion into iteration,
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the key enabling mechanism is the fact that Trampoline.more is a lazy operation.
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Trampoline in cyclops-react extends java.util.Supplier. Calling Trampoline.more we are basically creating
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a Supplier that defers the actual recursive call, and having defered the call we can move it outside of the recursive loop.
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This means we can define algorithms recursively in Java but execute them iteratively.*/
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public interface Trampoline<T> {
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T get();
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/**
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* @return next stage
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*/
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default Trampoline<T> jump() {
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return this;
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}
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default T result() {
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return get();
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}
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/**
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* @return true if complete
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*
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*/
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default boolean complete() {
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return true;
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}
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/**
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* Created a completed Trampoline
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*
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* @param result Completed result
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* @return Completed Trampoline
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*/
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static <T> Trampoline<T> done(final T result) {
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return () -> result;
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}
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/**
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* Create a Trampoline that has more work to do
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*
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* @param trampoline Next stage in Trampoline
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* @return Trampoline with more work
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*/
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static <T> Trampoline<T> more(final Trampoline<Trampoline<T>> trampoline) {
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return new Trampoline<T>() {
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@Override
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public boolean complete() {
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return false;
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}
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@Override
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public Trampoline<T> jump() {
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return trampoline.result();
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}
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@Override
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public T get() {
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return trampoline(this);
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}
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T trampoline(final Trampoline<T> trampoline) {
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return Stream.iterate(trampoline, Trampoline::jump)
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.filter(Trampoline::complete)
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.findFirst()
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.get()
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.result();
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}
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};
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}
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}

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

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/**
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* The MIT License
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* Copyright (c) 2014-2016 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.trampoline;
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import lombok.extern.slf4j.Slf4j;
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/**
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* <div>
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* By representing a computation in one of 2 states
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(completed with result, or a reference to the reminder of the computation,
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something like the way a java.util.Supplier does)
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it is possible to implement algorithms recursively in Java without blowing the stack
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and to interleave the execution of functions without hard coding them together or even using threads.
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</div>
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<div>
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Trampoline has 2 state : [done], [ more]
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</div>
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When get is called on the returned Trampoline, internally it will iterate calling ‘jump’
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on the returned Trampoline as long as the concrete instance returned is More,
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stopping once the returned instance is Done. Essential we convert looping via recursion into iteration,
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the key enabling mechanism is the fact that Trampoline.more is a lazy operation.
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Trampoline in cyclops-react extends java.util.Supplier. Calling Trampoline.more we are basically creating
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a Supplier that defers the actual recursive call, and having defered the call we can move it outside of the recursive loop.
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This means we can define algorithms recursively in Java but execute them iteratively.
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*/
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@Slf4j
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public class TrampolineApp {
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public static void main(String[] args) {
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log.info("start pattern");
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Integer result = loop(10, 1).result();
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log.info("result {}" ,result);
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}
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/**
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* Manager for pattern.
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* */
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public static Trampoline<Integer> loop(int times,int prod){
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if(times==0)
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return Trampoline.done(prod);
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else
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return Trampoline.more(()->loop(times-1,prod*times));
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}
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}

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

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

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