Pr/1235 Review (#1250)

* Add simple implementation for strangler pattern.

* Add strangler pattern in pom.xml.

* change package name

* Revert "change package name"

This reverts commit 430bd9073ea7bea6430586a0953c77f1798aacc8.

* Code review for strangler

Delete final of method parameters.
Add final to private members.
Change package name.

* Revert "Code review for strangler"

This reverts commit d5063567083e0348d678a938bd749e17343bcb8e.

* Revert "Revert "Code review for strangler""

This reverts commit c8fd65fda782749c4f74f6de85da0f271d3c48a8.

* Remove unnecessary files

pom.xml

@@ -190,6 +190,7 @@
         <module>combinator</module>
         <module>update-method</module>
         <module>leader-followers</module>
+        <module>strangler</module>
         <module>arrange-act-assert</module>
     </modules>
 

strangler/README.md

@@ -0,0 +1,31 @@
+---
+layout: pattern
+title: Strangler
+folder: strangler
+permalink: /patterns/strangler/
+categories: Structural
+tags:
+ - Extensibility
+---
+
+## Intent
+Incrementally migrate a legacy system by gradually replacing specific pieces of functionality
+with new applications and services. As features from the legacy system are replaced, the new
+system eventually covers all the old system's features and may has its own new features, then
+strangling the old system and allowing you to decommission it.
+
+## Class diagram
+![alt text](./etc/strangler.png "Strangler")
+
+## Applicability
+This strangler pattern is a safe way to phase one thing out for something better, cheaper, or 
+more expandable. Especially when you want to update legacy system with new techniques and need 
+continuously develop new features at the same time. Note that this pattern indeed need extra effort, 
+so usually use it when the system is not so simple.
+
+## Credits
+
+* [Strangler pattern](https://docs.microsoft.com/en-us/azure/architecture/patterns/strangler#context-and-problem)
+* [Legacy Application Strangulation : Case Studies](https://paulhammant.com/2013/07/14/legacy-application-strangulation-case-studies/)
+
+

strangler/etc/strangler.puml

@@ -0,0 +1,61 @@
+@startuml
+
+package com.iluwatar.strangler {
+    class App {
+        + main(args : String[]) {static}
+    }
+
+    class OldArithmetic {
+        - LOGGER : Logger {static}
+        - VERSION : String {static}
+        - source : OldSource
+        + sum(nums : int...)
+        + mul(nums : int...)
+    }
+
+    class HalfArithmetic {
+        - LOGGER : Logger {static}
+        - VERSION : String {static}
+        - oldSource : OldSource
+        - newSource : HalfSource
+        + sum(nums : int...)
+        + mul(nums : int...)
+        + ifHasZero(nums : int...)
+    }
+
+    class NewArithmetic {
+        - LOGGER : Logger {static}
+        - VERSION : String {static}
+        - source : NewSource
+        + sum(nums : int...)
+        + mul(nums : int...)
+        + ifHasZero(nums : int...)
+    }
+
+    class OldSource {
+        - LOGGER : Logger {static}
+        - VERSION : String {static}
+        + accumulateSum(nums : int...)
+        + accumulateMul(nums : int...)
+    }
+
+    class HalfSource {
+        - LOGGER : Logger {static}
+        - VERSION : String {static}
+        + accumulateSum(nums : int...)
+        + ifNonZero(nums : int...)
+    }
+
+    class NewSource {
+        - LOGGER : Logger {static}
+        - VERSION : String {static}
+        + accumulateSum(nums : int...)
+        + accumulateMul(nums : int...)
+        + ifNonZero(nums : int...)
+    }
+}
+OldArithmetic o--> OldSource
+HalfArithmetic o--> OldSource
+HalfArithmetic o--> HalfSource
+NewArithmetic o--> NewSource
+@enduml

strangler/pom.xml

@@ -0,0 +1,66 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    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.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>java-design-patterns</artifactId>
+        <groupId>com.iluwatar</groupId>
+        <version>1.23.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>strangler</artifactId>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <configuration>
+                            <archive>
+                                <manifest>
+                                    <mainClass>com.iluwatar.strangler.App</mainClass>
+                                </manifest>
+                            </archive>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
+
+</project>

strangler/src/main/java/com/iluwatar/strangler/App.java

@@ -0,0 +1,69 @@
+/*
+ * 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.strangler;
+
+/**
+ *
+ * <p>The Strangler pattern is a software design pattern that incrementally migrate a legacy
+ * system by gradually replacing specific pieces of functionality with new applications and
+ * services. As features from the legacy system are replaced, the new system eventually
+ * replaces all of the old system's features, strangling the old system and allowing you
+ * to decommission it.</p>
+ *
+ * <p>This pattern is not only about updating but also enhancement.</p>
+ *
+ * <p>In this example, {@link OldArithmetic} indicates old system and its implementation depends
+ * on its source ({@link OldSource}). Now we tend to update system with new techniques and
+ * new features. In reality, the system may too complex, so usually need gradual migration.
+ * {@link HalfArithmetic} indicates system in the process of migration, its implementation
+ * depends on old one ({@link OldSource}) and under development one ({@link HalfSource}). The
+ * {@link HalfSource} covers part of {@link OldSource} and add new functionality. You can release
+ * this version system with new features, which also supports old version system functionalities.
+ * After whole migration, the new system ({@link NewArithmetic}) only depends on new source
+ * ({@link NewSource}).</p>
+ *
+ */
+public class App {
+  /**
+   * Program entry point.
+   * @param args command line args
+   */
+  public static void main(final String[] args) {
+    final var nums = new int[]{1, 2, 3, 4, 5};
+    //Before migration
+    final var oldSystem = new OldArithmetic(new OldSource());
+    oldSystem.sum(nums);
+    oldSystem.mul(nums);
+    //In process of migration
+    final var halfSystem = new HalfArithmetic(new HalfSource(), new OldSource());
+    halfSystem.sum(nums);
+    halfSystem.mul(nums);
+    halfSystem.ifHasZero(nums);
+    //After migration
+    final var newSystem = new NewArithmetic(new NewSource());
+    newSystem.sum(nums);
+    newSystem.mul(nums);
+    newSystem.ifHasZero(nums);
+  }
+}

strangler/src/main/java/com/iluwatar/strangler/HalfArithmetic.java

@@ -0,0 +1,74 @@
+/*
+ * 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.strangler;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * System under migration. Depends on old version source ({@link OldSource}) and
+ * developing one ({@link HalfSource}).
+ */
+public class HalfArithmetic {
+  private static final Logger LOGGER = LoggerFactory.getLogger(HalfArithmetic.class);
+  private static final String VERSION = "1.5";
+
+  private final HalfSource newSource;
+  private final OldSource oldSource;
+
+  public HalfArithmetic(HalfSource newSource, OldSource oldSource) {
+    this.newSource = newSource;
+    this.oldSource = oldSource;
+  }
+
+  /**
+   * Accumulate sum.
+   * @param nums numbers need to add together
+   * @return accumulate sum
+   */
+  public int sum(int... nums) {
+    LOGGER.info("Arithmetic sum {}", VERSION);
+    return newSource.accumulateSum(nums);
+  }
+
+  /**
+   * Accumulate multiplication.
+   * @param nums numbers need to multiply together
+   * @return accumulate multiplication
+   */
+  public int mul(int... nums) {
+    LOGGER.info("Arithmetic mul {}", VERSION);
+    return oldSource.accumulateMul(nums);
+  }
+
+  /**
+   * Chech if has any zero.
+   * @param nums numbers need to check
+   * @return  if has any zero, return true, else, return false
+   */
+  public boolean ifHasZero(int... nums) {
+    LOGGER.info("Arithmetic check zero {}", VERSION);
+    return !newSource.ifNonZero(nums);
+  }
+}

strangler/src/main/java/com/iluwatar/strangler/HalfSource.java

@@ -0,0 +1,54 @@
+/*
+ * 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.strangler;
+
+import java.util.Arrays;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Source under development. Replace part of old source and has added some new features.
+ */
+public class HalfSource {
+  private static final Logger LOGGER = LoggerFactory.getLogger(HalfSource.class);
+  private static final  String VERSION = "1.5";
+
+  /**
+   * Implement accumulate sum with new technique.
+   * Replace old one in {@link OldSource}
+   */
+  public int accumulateSum(int... nums) {
+    LOGGER.info("Source module {}", VERSION);
+    return Arrays.stream(nums).reduce(0, Integer::sum);
+  }
+
+  /**
+   * Check if all number is not zero.
+   * New feature.
+   */
+  public boolean ifNonZero(int... nums) {
+    LOGGER.info("Source module {}", VERSION);
+    return Arrays.stream(nums).allMatch(num -> num != 0);
+  }
+}

strangler/src/main/java/com/iluwatar/strangler/NewArithmetic.java

@@ -0,0 +1,71 @@
+/*
+ * 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.strangler;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * System after whole migration. Only depends on new version source ({@link NewSource}).
+ */
+public class NewArithmetic {
+  private static final Logger LOGGER = LoggerFactory.getLogger(NewArithmetic.class);
+  private static final  String VERSION = "2.0";
+
+  private final NewSource source;
+
+  public NewArithmetic(NewSource source) {
+    this.source = source;
+  }
+
+  /**
+   * Accumulate sum.
+   * @param nums numbers need to add together
+   * @return accumulate sum
+   */
+  public int sum(int... nums) {
+    LOGGER.info("Arithmetic sum {}", VERSION);
+    return source.accumulateSum(nums);
+  }
+
+  /**
+   * Accumulate multiplication.
+   * @param nums numbers need to multiply together
+   * @return accumulate multiplication
+   */
+  public int mul(int... nums) {
+    LOGGER.info("Arithmetic mul {}", VERSION);
+    return source.accumulateMul(nums);
+  }
+
+  /**
+   * Chech if has any zero.
+   * @param nums numbers need to check
+   * @return  if has any zero, return true, else, return false
+   */
+  public boolean ifHasZero(int... nums) {
+    LOGGER.info("Arithmetic check zero {}", VERSION);
+    return !source.ifNonZero(nums);
+  }
+}

strangler/src/main/java/com/iluwatar/strangler/NewSource.java

@@ -0,0 +1,56 @@
+/*
+ * 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.strangler;
+
+import java.util.Arrays;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * New source. Completely covers functionalities of old source with new techniques
+ * and also has some new features.
+ */
+public class NewSource {
+  private static final Logger LOGGER = LoggerFactory.getLogger(NewSource.class);
+  private static final  String VERSION = "2.0";
+
+  public int accumulateSum(int... nums) {
+    LOGGER.info("Source module {}", VERSION);
+    return Arrays.stream(nums).reduce(0, Integer::sum);
+  }
+
+  /**
+   * Implement accumulate multiply with new technique.
+   * Replace old one in {@link OldSource}
+   */
+  public int accumulateMul(int... nums) {
+    LOGGER.info("Source module {}", VERSION);
+    return Arrays.stream(nums).reduce(1, (a, b) -> a * b);
+  }
+
+  public boolean ifNonZero(int... nums) {
+    LOGGER.info("Source module {}", VERSION);
+    return Arrays.stream(nums).allMatch(num -> num != 0);
+  }
+}

strangler/src/main/java/com/iluwatar/strangler/OldArithmetic.java

@@ -0,0 +1,61 @@
+/*
+ * 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.strangler;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Old version system depends on old version source ({@link OldSource}).
+ */
+public class OldArithmetic {
+  private static final Logger LOGGER = LoggerFactory.getLogger(OldArithmetic.class);
+  private static final  String VERSION = "1.0";
+
+  private final OldSource source;
+
+  public OldArithmetic(OldSource source) {
+    this.source = source;
+  }
+
+  /**
+   * Accumulate sum.
+   * @param nums numbers need to add together
+   * @return accumulate sum
+   */
+  public int sum(int... nums) {
+    LOGGER.info("Arithmetic sum {}", VERSION);
+    return source.accumulateSum(nums);
+  }
+
+  /**
+   * Accumulate multiplication.
+   * @param nums numbers need to multiply together
+   * @return accumulate multiplication
+   */
+  public int mul(int... nums) {
+    LOGGER.info("Arithmetic mul {}", VERSION);
+    return source.accumulateMul(nums);
+  }
+}

strangler/src/main/java/com/iluwatar/strangler/OldSource.java

@@ -0,0 +1,59 @@
+/*
+ * 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.strangler;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Old source with techniques out of date.
+ */
+public class OldSource {
+  private static final Logger LOGGER = LoggerFactory.getLogger(OldSource.class);
+  private static final String VERSION = "1.0";
+
+  /**
+   * Implement accumulate sum with old technique.
+   */
+  public int accumulateSum(int... nums) {
+    LOGGER.info("Source module {}", VERSION);
+    var sum = 0;
+    for (final var num : nums) {
+      sum += num;
+    }
+    return sum;
+  }
+
+  /**
+   * Implement accumulate multiply with old technique.
+   */
+  public int accumulateMul(int... nums) {
+    LOGGER.info("Source module {}", VERSION);
+    var sum = 1;
+    for (final var num : nums) {
+      sum *= num;
+    }
+    return sum;
+  }
+}

strangler/src/test/java/com/iluwatar/strangler/AppTest.java

@@ -0,0 +1,36 @@
+/*
+ * 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.strangler;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Application test
+ */
+public class AppTest {
+  @Test
+  public void test() {
+    App.main(new String[]{});
+  }
+}

strangler/src/test/java/com/iluwatar/strangler/HalfArithmeticTest.java

@@ -0,0 +1,50 @@
+/*
+ * 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.strangler;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Test methods in HalfArithmetic
+ */
+class HalfArithmeticTest {
+  private static final HalfArithmetic arithmetic = new HalfArithmetic(new HalfSource(), new OldSource());
+
+  @Test
+  public void testSum() {
+    assertEquals(0, arithmetic.sum(-1, 0, 1));
+  }
+
+  @Test
+  public void testMul() {
+    assertEquals(0, arithmetic.mul(-1, 0, 1));
+  }
+
+  @Test
+  public void testIfHasZero() {
+    assertTrue(arithmetic.ifHasZero(-1, 0, 1));
+  }
+}

strangler/src/test/java/com/iluwatar/strangler/HalfSourceTest.java

@@ -0,0 +1,47 @@
+/*
+ * 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.strangler;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Test methods in HalfSource
+ */
+public class HalfSourceTest {
+  private static final HalfSource source = new HalfSource();
+
+  @Test
+  public void testAccumulateSum() {
+    assertEquals(0, source.accumulateSum(-1, 0, 1));
+  }
+
+  @Test
+  public void testIfNonZero() {
+    assertFalse(source.ifNonZero(-1, 0, 1));
+  }
+}

strangler/src/test/java/com/iluwatar/strangler/NewArithmeticTest.java

@@ -0,0 +1,50 @@
+/*
+ * 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.strangler;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Test methods in NewArithmetic
+ */
+class NewArithmeticTest {
+  private static final NewArithmetic arithmetic = new NewArithmetic(new NewSource());
+
+  @Test
+  public void testSum() {
+    assertEquals(0, arithmetic.sum(-1, 0, 1));
+  }
+
+  @Test
+  public void testMul() {
+    assertEquals(0, arithmetic.mul(-1, 0, 1));
+  }
+
+  @Test
+  public void testIfHasZero() {
+    assertTrue(arithmetic.ifHasZero(-1, 0, 1));
+  }
+}

strangler/src/test/java/com/iluwatar/strangler/NewSourceTest.java

@@ -0,0 +1,51 @@
+/*
+ * 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.strangler;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+/**
+ * Test methods in NewSource
+ */
+public class NewSourceTest {
+  private static final NewSource source = new NewSource();
+
+  @Test
+  public void testAccumulateSum() {
+    assertEquals(0, source.accumulateSum(-1, 0, 1));
+  }
+
+  @Test
+  public void testAccumulateMul() {
+    assertEquals(0, source.accumulateMul(-1, 0, 1));
+  }
+
+  @Test
+  public void testIfNonZero() {
+    assertFalse(source.ifNonZero(-1, 0, 1));
+  }
+}

strangler/src/test/java/com/iluwatar/strangler/OldArithmeticTest.java

@@ -0,0 +1,45 @@
+/*
+ * 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.strangler;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Test methods in OldArithmetic
+ */
+class OldArithmeticTest {
+  private static final OldArithmetic arithmetic = new OldArithmetic(new OldSource());
+
+  @Test
+  public void testSum() {
+    assertEquals(0, arithmetic.sum(-1, 0, 1));
+  }
+
+  @Test
+  public void testMul() {
+    assertEquals(0, arithmetic.mul(-1, 0, 1));
+  }
+}

strangler/src/test/java/com/iluwatar/strangler/OldSourceTest.java

@@ -0,0 +1,45 @@
+/*
+ * 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.strangler;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Test methods in OldSource
+ */
+public class OldSourceTest {
+  private static final OldSource source = new OldSource();
+
+  @Test
+  public void testAccumulateSum() {
+    assertEquals(0, source.accumulateSum(-1, 0, 1));
+  }
+
+  @Test
+  public void testAccumulateMul() {
+    assertEquals(0, source.accumulateMul(-1, 0, 1));
+  }
+}