#66 Balking Pattern

balking/README.md

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+---
+layout: pattern
+title: Balking
+folder: balking
+permalink: /patterns/balking/
+categories: Concurrency
+tags:
+ - Java
+ - Difficulty-Beginner
+---
+
+## Intent
+Balking Pattern is used to prevent an object from executing certain code if it is an
+incomplete or inappropriate state
+
+![alt text](./etc/balking.png "Balking")
+
+## Applicability
+Use the Balking pattern when
+
+*you want to invoke an action on an object only when it is in a particular state
+*objects are generally only in a state that is prone to balking temporarily
+but for an unknown amount of time

balking/etc/balking.ucls

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+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.1.13" icons="true" automaticImage="PNG" always-add-relationships="false" 
+  generalizations="true" realizations="true" associations="true" dependencies="false" nesting-relationships="true" 
+  router="FAN">  
+  <class id="1" language="java" name="com.iluwatar.balking.App" project="balking" 
+    file="/balking/src/main/java/com/iluwatar/balking/App.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="113" width="114" x="135" y="103"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="2" language="java" name="com.iluwatar.balking.WashingMachine" project="balking" 
+    file="/balking/src/main/java/com/iluwatar/balking/WashingMachine.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="149" width="268" x="289" y="103"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <enumeration id="3" language="java" name="com.iluwatar.balking.WashingMachineState" project="balking" 
+    file="/balking/src/main/java/com/iluwatar/balking/WashingMachineState.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="113" width="192" x="289" y="292"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </enumeration>  
+  <association id="4">    
+    <end type="SOURCE" refId="2" navigable="false">      
+      <attribute id="5" name="washingMachineState"/>      
+      <multiplicity id="6" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="3" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
+</class-diagram>

balking/etc/balking.urm.puml

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+@startuml
+package com.iluwatar.balking {
+  class App {
+    - LOGGER : Logger {static}
+    + App()
+    + main(args : String[]) {static}
+  }
+  class WashingMachine {
+    - LOGGER : Logger {static}
+    - washingMachineState : WashingMachineState
+    + WashingMachine()
+    + endOfWashing()
+    + getWashingMachineState() : WashingMachineState
+    + wash()
+  }
+  enum WashingMachineState {
+    + ENABLED {static}
+    + WASHING {static}
+    + valueOf(name : String) : WashingMachineState {static}
+    + values() : WashingMachineState[] {static}
+  }
+}
+WashingMachine -->  "-washingMachineState" WashingMachineState
+@enduml

balking/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    The MIT License
+    Copyright (c) 2014 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>1.14.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>balking</artifactId>
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+
+</project>

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

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.balking;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+public class App {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+
+  /**
+   * @param args the command line arguments - not used
+   */
+  public static void main(String... args) {
+    final WashingMachine washingMachine = new WashingMachine();
+    ExecutorService executorService = Executors.newFixedThreadPool(3);
+    for (int i = 0; i < 3; i++) {
+      executorService.execute(washingMachine::wash);
+    }
+    executorService.shutdown();
+    try {
+      executorService.awaitTermination(10, TimeUnit.SECONDS);
+    } catch (InterruptedException ie) {
+      LOGGER.error("ERROR: Waiting on executor service shutdown!");
+    }
+  }
+
+}

balking/src/main/java/com/iluwatar/balking/WashingMachine.java

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.balking;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class WashingMachine {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(WashingMachine.class);
+
+  private WashingMachineState washingMachineState;
+
+  public WashingMachine() {
+    washingMachineState = WashingMachineState.ENABLED;
+  }
+
+  public WashingMachineState getWashingMachineState() {
+    return washingMachineState;
+  }
+
+  /**
+   * Method responsible for washing
+   * if the object is in appropriate state
+   */
+  public void wash() {
+    synchronized (this) {
+      LOGGER.info("{}: Actual machine state: {}", Thread.currentThread().getName(), getWashingMachineState());
+      if (washingMachineState == WashingMachineState.WASHING) {
+        LOGGER.error("ERROR: Cannot wash if the machine has been already washing!");
+        return;
+      }
+      washingMachineState = WashingMachineState.WASHING;
+    }
+    LOGGER.info("{}: Doing the washing", Thread.currentThread().getName());
+    try {
+      Thread.sleep(50);
+    } catch (InterruptedException ie) {
+      ie.printStackTrace();
+    }
+    endOfWashing();
+  }
+
+  /**
+   * Method responsible of ending the washing
+   * by changing machine state
+   */
+  public synchronized void endOfWashing() {
+    washingMachineState = WashingMachineState.ENABLED;
+    LOGGER.info("{}: Washing completed.", Thread.currentThread().getId());
+  }
+
+}

balking/src/main/java/com/iluwatar/balking/WashingMachineState.java

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.balking;
+
+public enum WashingMachineState {ENABLED, WASHING}

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

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.balking;
+
+public class AppTest {
+  @org.junit.Test
+  public void main() throws Exception {
+    String[] args = {};
+    App.main(args);
+  }
+
+}

balking/src/test/java/com/iluwatar/balking/WashingMachineTest.java

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.balking;
+
+import org.junit.Test;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.*;
+
+public class WashingMachineTest {
+
+  private volatile WashingMachineState machineStateGlobal;
+
+  @Test
+  public void wash() throws Exception {
+    WashingMachine washingMachine = new WashingMachine();
+    ExecutorService executorService = Executors.newFixedThreadPool(2);
+    executorService.execute(washingMachine::wash);
+    executorService.execute(() -> {
+      washingMachine.wash();
+      machineStateGlobal = washingMachine.getWashingMachineState();
+    });
+    executorService.shutdown();
+    try {
+      executorService.awaitTermination(10, TimeUnit.SECONDS);
+    } catch (InterruptedException ie) {
+      ie.printStackTrace();
+    }
+    assertEquals(WashingMachineState.WASHING, machineStateGlobal);
+  }
+
+  @Test
+  public void endOfWashing() throws Exception {
+    WashingMachine washingMachine = new WashingMachine();
+    washingMachine.wash();
+    assertEquals(WashingMachineState.ENABLED, washingMachine.getWashingMachineState());
+  }
+
+}