The Command Pattern in Java - BAEL-1722 (#4048)

* Initial Commit

* Update pom.xml

* Fix unit tests format

* Fix unit test class name

* Update OpenTextFileOPerationUnitTest.java

* Delete OpenTextFileOPerationUnitTest.java

* Delete OpenTextFileOPerationUnitTest.java

* Add unit test class

* Update TextFileOperationExecutorUnitTest.java

* Update TextFileUnitTest.java

patterns/behavioral-patterns/pom.xml

@@ -19,6 +19,18 @@
             <version>4.12</version>
             <scope>test</scope>
         </dependency>
+	<dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-core</artifactId>
+            <version>1.3</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.8.0</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

patterns/behavioral-patterns/src/main/java/com/baeldung/pattern/command/client/TextFileApplication.java

@@ -0,0 +1,19 @@
+package com.baeldung.pattern.command.client;
+
+import com.baeldung.pattern.command.command.OpenTextFileOperation;
+import com.baeldung.pattern.command.command.SaveTextFileOperation;
+import com.baeldung.pattern.command.command.TextFileOperation;
+import com.baeldung.pattern.command.invoker.TextFileOperationExecutor;
+import com.baeldung.pattern.command.receiver.TextFile;
+
+public class TextFileApplication {
+    
+    public static void main(String[] args) {
+        
+        TextFileOperation openTextFileOperation = new OpenTextFileOperation(new TextFile("file1.txt"));
+        TextFileOperation saveTextFileOperation = new SaveTextFileOperation(new TextFile("file2.txt"));
+        TextFileOperationExecutor textFileOperationExecutor = new TextFileOperationExecutor();
+        System.out.println(textFileOperationExecutor.executeOperation(openTextFileOperation));
+        System.out.println(textFileOperationExecutor.executeOperation(saveTextFileOperation));
+    }   
+}

patterns/behavioral-patterns/src/main/java/com/baeldung/pattern/command/command/OpenTextFileOperation.java

@@ -0,0 +1,17 @@
+package com.baeldung.pattern.command.command;
+
+import com.baeldung.pattern.command.receiver.TextFile;
+
+public class OpenTextFileOperation implements TextFileOperation {
+
+    private final TextFile textFile;
+    
+    public OpenTextFileOperation(TextFile textFile) {
+        this.textFile = textFile;
+    }
+    
+    @Override
+    public String execute() {
+        return textFile.open();
+    }
+}

patterns/behavioral-patterns/src/main/java/com/baeldung/pattern/command/command/SaveTextFileOperation.java

@@ -0,0 +1,17 @@
+package com.baeldung.pattern.command.command;
+
+import com.baeldung.pattern.command.receiver.TextFile;
+
+public class SaveTextFileOperation implements TextFileOperation {
+    
+    private final TextFile textFile;
+    
+    public SaveTextFileOperation(TextFile textFile) {
+        this.textFile = textFile;
+    }
+    
+    @Override
+    public String execute() {
+        return textFile.save();
+    }
+}

patterns/behavioral-patterns/src/main/java/com/baeldung/pattern/command/command/TextFileOperation.java

@@ -0,0 +1,8 @@
+package com.baeldung.pattern.command.command;
+
+@FunctionalInterface
+public interface TextFileOperation {
+    
+    String execute();
+    
+}

patterns/behavioral-patterns/src/main/java/com/baeldung/pattern/command/invoker/TextFileOperationExecutor.java

@@ -0,0 +1,15 @@
+package com.baeldung.pattern.command.invoker;
+
+import com.baeldung.pattern.command.command.TextFileOperation;
+import java.util.ArrayList;
+import java.util.List;
+
+public class TextFileOperationExecutor {
+    
+    private final List<TextFileOperation> textFileOperations = new ArrayList<>();
+    
+    public String executeOperation(TextFileOperation textFileOperation) {
+        textFileOperations.add(textFileOperation);
+        return textFileOperation.execute();
+    }
+}

patterns/behavioral-patterns/src/main/java/com/baeldung/pattern/command/receiver/TextFile.java

@@ -0,0 +1,34 @@
+package com.baeldung.pattern.command.receiver;
+
+public class TextFile {
+    
+    private final String name;
+    
+    public TextFile(String name) {
+        this.name = name;
+    }
+    
+    public String open() {
+        return "Opening file " + name;
+    }
+    
+    public String read() {  
+        return "Reading file " + name;
+    }
+    
+    public String write() {  
+        return "Writing to file " + name;
+    }
+    
+    public String save() {  
+        return "Saving file " + name;
+    }
+    
+    public String copy() {  
+        return "Copying file " + name;
+    }
+    
+    public String paste() {  
+        return "Pasting file " + name;
+    }
+}

patterns/behavioral-patterns/src/test/java/com/baeldung/pattern/command/test/OpenTextFileOperationUnitTest.java

@@ -0,0 +1,16 @@
+package com.baeldung.pattern.command.test;
+
+import com.baeldung.pattern.command.command.OpenTextFileOperation;
+import com.baeldung.pattern.command.command.TextFileOperation;
+import com.baeldung.pattern.command.receiver.TextFile;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
+
+public class OpenTextFileOperationUnitTest {
+    
+    @Test
+    public void givenOpenTextFileOperationIntance_whenCalledExecuteMethod_thenOneAssertion() {
+        TextFileOperation openTextFileOperation = new OpenTextFileOperation(new TextFile("file1.txt"));
+        assertThat(openTextFileOperation.execute()).isEqualTo("Opening file file1.txt");
+    }
+}

patterns/behavioral-patterns/src/test/java/com/baeldung/pattern/command/test/SaveTextFileOperationUnitTest.java

@@ -0,0 +1,16 @@
+package com.baeldung.pattern.command.test;
+
+import com.baeldung.pattern.command.command.SaveTextFileOperation;
+import com.baeldung.pattern.command.command.TextFileOperation;
+import com.baeldung.pattern.command.receiver.TextFile;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
+
+public class SaveTextFileOperationUnitTest {
+    
+    @Test
+    public void givenSaveTextFileOperationIntance_whenCalledExecuteMethod_thenOneAssertion() {
+        TextFileOperation openTextFileOperation = new SaveTextFileOperation(new TextFile("file1.txt"));
+        assertThat(openTextFileOperation.execute()).isEqualTo("Saving file file1.txt");
+    }
+}

patterns/behavioral-patterns/src/test/java/com/baeldung/pattern/command/test/TextFileOperationExecutorUnitTest.java

@@ -0,0 +1,68 @@
+package com.baeldung.pattern.command.test;
+
+import com.baeldung.pattern.command.command.OpenTextFileOperation;
+import com.baeldung.pattern.command.command.SaveTextFileOperation;
+import com.baeldung.pattern.command.command.TextFileOperation;
+import com.baeldung.pattern.command.invoker.TextFileOperationExecutor;
+import com.baeldung.pattern.command.receiver.TextFile;
+import java.util.function.Function;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
+import org.junit.BeforeClass;
+
+public class TextFileOperationExecutorUnitTest {
+    
+    private static TextFileOperationExecutor textFileOperationExecutor;
+    
+    
+    @BeforeClass
+    public static void setUpTextFileOperationExecutor() {
+        textFileOperationExecutor = new TextFileOperationExecutor();
+    }
+    
+    @Test
+    public void givenTextFileOPerationExecutorInstance_whenCalledexecuteOperationWithOpenTextOperation_thenOneAssertion() {
+        TextFileOperation textFileOperation = new OpenTextFileOperation(new TextFile("file1.txt"));
+        assertThat(textFileOperationExecutor.executeOperation(textFileOperation)).isEqualTo("Opening file file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileOPerationExecutorInstance_whenCalledexecuteOperationWithSaveTextOperation_thenOneAssertion() {
+        TextFileOperation textFileOperation = new SaveTextFileOperation(new TextFile("file1.txt"));
+        assertThat(textFileOperationExecutor.executeOperation(textFileOperation)).isEqualTo("Saving file file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileOperationExecutorInstance_whenCalledexecuteOperationWithTextFileOpenLambda_thenOneAssertion() {
+        assertThat(textFileOperationExecutor.executeOperation(() -> {return "Opening file file1.txt";})).isEqualTo("Opening file file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileOperationExecutorInstance_whenCalledexecuteOperationWithTextFileSaveLambda_thenOneAssertion() {
+        assertThat(textFileOperationExecutor.executeOperation(() -> {return "Saving file file1.txt";})).isEqualTo("Saving file file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileOperationExecutorInstance_whenCalledexecuteOperationWithTextFileOpenMethodReferenceOfExistingObject_thenOneAssertion() {
+        TextFile textFile = new TextFile("file1.txt");
+        assertThat(textFileOperationExecutor.executeOperation(textFile::open)).isEqualTo("Opening file file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileOperationExecutorInstance_whenCalledexecuteOperationWithTextFileSaveMethodReferenceOfExistingObject_thenOneAssertion() {
+        TextFile textFile = new TextFile("file1.txt");
+        assertThat(textFileOperationExecutor.executeOperation(textFile::save)).isEqualTo("Saving file file1.txt");
+    }
+    
+    @Test
+    public void givenOpenTextFileOperationExecuteMethodReference_whenCalledApplyMethod_thenOneAssertion() {
+        Function<OpenTextFileOperation, String> executeMethodReference = OpenTextFileOperation::execute;
+        assertThat(executeMethodReference.apply(new OpenTextFileOperation(new TextFile("file1.txt")))).isEqualTo("Opening file file1.txt"); 
+    }
+    
+    @Test
+    public void givenSaveTextFileOperationExecuteMethodReference_whenCalledApplyMethod_thenOneAssertion() {
+        Function<SaveTextFileOperation, String> executeMethodReference = SaveTextFileOperation::execute;
+        assertThat(executeMethodReference.apply(new SaveTextFileOperation(new TextFile("file1.txt")))).isEqualTo("Saving file file1.txt"); 
+    }
+}

patterns/behavioral-patterns/src/test/java/com/baeldung/pattern/command/test/TextFileUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.pattern.command.test;
+
+import com.baeldung.pattern.command.receiver.TextFile;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
+import org.junit.BeforeClass;
+
+public class TextFileUnitTest {
+    
+    private static TextFile textFile;
+    
+    
+    @BeforeClass
+    public static void setUpTextFileInstance() {
+        textFile = new TextFile("file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileInstance_whenCalledopenMethod_thenOneAssertion() {
+        assertThat(textFile.open()).isEqualTo("Opening file file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileInstance_whenCalledwriteMethod_thenOneAssertion() {
+        assertThat(textFile.write()).isEqualTo("Writing to file file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileInstance_whenCalledsaveMethod_thenOneAssertion() {
+        assertThat(textFile.save()).isEqualTo("Saving file file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileInstance_whenCalledcopyMethod_thenOneAssertion() {
+        assertThat(textFile.copy()).isEqualTo("Copying file file1.txt");
+    }
+    
+    @Test
+    public void givenTextFileInstance_whenCalledpasteMethod_thenOneAssertion() {
+        assertThat(textFile.paste()).isEqualTo("Pasting file file1.txt");
+    }
+}