Merge pull request #24 from darbyluv2code/feature/add-interpreter-pattern

Add Interpreter Pattern

Author: darbyluv2code

section-04-behavioral-design-patterns/18-interpreter/pom.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.luv2code</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.0</version>
+
+    <properties>
+        <maven.compiler.source>25</maven.compiler.source>
+        <maven.compiler.target>25</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+</project>

section-04-behavioral-design-patterns/18-interpreter/src/main/java/com/luv2code/designpatterns/behavioral/interpreter/ChatContext.java

@@ -0,0 +1,19 @@
+package com.luv2code.designpatterns.behavioral.interpreter;
+
+/**
+ * Role: Context
+ *
+ * Holds the shared state passed to every expression during interpretation.
+ */
+public class ChatContext {
+
+    private String currentUser;
+
+    public ChatContext(String currentUser) {
+        this.currentUser = currentUser;
+    }
+
+    public String getCurrentUser() {
+        return currentUser;
+    }
+}

section-04-behavioral-design-patterns/18-interpreter/src/main/java/com/luv2code/designpatterns/behavioral/interpreter/CommandParser.java

@@ -0,0 +1,43 @@
+package com.luv2code.designpatterns.behavioral.interpreter;
+
+/**
+ * Role: Helper (Parser)
+ *
+ * Parses a raw command string and builds the appropriate Expression.
+ *
+ * Not part of the GoF pattern itself ... this is the caller that constructs
+ * and triggers the expressions.
+ */
+public class CommandParser {
+
+    public Expression parse(String inputCommand) {
+
+        if (inputCommand == null || inputCommand.isBlank()) {
+            return new InvalidCommandExpression("empty input");
+        }
+
+        String trimmedInput = inputCommand.trim();
+        String[] parts = trimmedInput.split("\\s+", 2);
+
+        String commandName = parts[0];
+        String argument = parts.length > 1 ? parts[1] : "";
+
+        return switch (commandName) {
+            case "/join" -> new JoinExpression(argument);
+            case "/mute" -> new MuteExpression(argument);
+            case "/remind" -> new RemindExpression(argument);
+            default -> new InvalidCommandExpression(commandName);
+        };
+    }
+}
+
+
+
+
+
+
+
+
+
+
+

section-04-behavioral-design-patterns/18-interpreter/src/main/java/com/luv2code/designpatterns/behavioral/interpreter/Expression.java

@@ -0,0 +1,11 @@
+package com.luv2code.designpatterns.behavioral.interpreter;
+
+/**
+ * Role: Abstract Expression
+ *
+ * Declares the interpret() method that all expressions must implement.
+ */
+public interface Expression {
+
+    void interpret(ChatContext chatContext);
+}

section-04-behavioral-design-patterns/18-interpreter/src/main/java/com/luv2code/designpatterns/behavioral/interpreter/InvalidCommandExpression.java

@@ -0,0 +1,20 @@
+package com.luv2code.designpatterns.behavioral.interpreter;
+
+/**
+ * Role: Concrete / Terminal Expression
+ *
+ * Handles unrecognized commands by reporting an error.
+ */
+public class InvalidCommandExpression implements Expression {
+
+    private String commandText;
+
+    public InvalidCommandExpression(String commandText) {
+        this.commandText = commandText;
+    }
+
+    @Override
+    public void interpret(ChatContext chatContext) {
+        System.out.println("[Error] Invalid command: " + commandText);
+    }
+}

section-04-behavioral-design-patterns/18-interpreter/src/main/java/com/luv2code/designpatterns/behavioral/interpreter/JoinExpression.java

@@ -0,0 +1,21 @@
+package com.luv2code.designpatterns.behavioral.interpreter;
+
+/**
+ * Role: Concrete / Terminal Expression
+ *
+ * Handles the /join command by adding the user to a chat room.
+ */
+public class JoinExpression implements Expression{
+
+    private String roomName;
+
+    public JoinExpression(String roomName) {
+        this.roomName = roomName;
+    }
+
+    @Override
+    public void interpret(ChatContext chatContext) {
+        System.out.println("[Join] " + chatContext.getCurrentUser()
+                + " joined room: " + roomName);
+    }
+}

section-04-behavioral-design-patterns/18-interpreter/src/main/java/com/luv2code/designpatterns/behavioral/interpreter/MainApp.java

@@ -0,0 +1,43 @@
+package com.luv2code.designpatterns.behavioral.interpreter;
+
+/**
+ * Role: Client
+ *
+ * Drives the demo by sending sample chat commands through the interpreter.
+ */
+public class MainApp {
+
+    static void main() {
+
+        System.out.println("--- Demo: Chat Command Interpreter ---");
+
+        CommandParser commandParser = new CommandParser();
+
+        runCommand("/join java-room", "Angel", commandParser);
+        runCommand("/mute Liam", "Angel", commandParser);
+        runCommand("/remind Team meeting at 3pm", "Angel", commandParser);
+        runCommand("/dance now", "Angel", commandParser);
+
+    }
+
+    private static void runCommand(String inputCommand,
+                                   String currentUser,
+                                   CommandParser commandParser) {
+
+        ChatContext chatContext = new ChatContext(currentUser);
+
+        System.out.println("\nInput: " + inputCommand);
+
+        Expression parsedExpression = commandParser.parse(inputCommand);
+        parsedExpression.interpret(chatContext);
+    }
+}
+
+
+
+
+
+
+
+
+

section-04-behavioral-design-patterns/18-interpreter/src/main/java/com/luv2code/designpatterns/behavioral/interpreter/MuteExpression.java

@@ -0,0 +1,21 @@
+package com.luv2code.designpatterns.behavioral.interpreter;
+
+/**
+ * Role: Concrete / Terminal Expression
+ *
+ * Handles the /mute command by silencing a target user.
+ */
+public class MuteExpression implements Expression {
+
+    private String targetUser;
+
+    public MuteExpression(String targetUser) {
+        this.targetUser = targetUser;
+    }
+
+    @Override
+    public void interpret(ChatContext chatContext) {
+        System.out.println("[Mute] " + chatContext.getCurrentUser()
+                + " muted user: " + targetUser);
+    }
+}

section-04-behavioral-design-patterns/18-interpreter/src/main/java/com/luv2code/designpatterns/behavioral/interpreter/RemindExpression.java

@@ -0,0 +1,21 @@
+package com.luv2code.designpatterns.behavioral.interpreter;
+
+/**
+ * Role: Concrete / Terminal Expression
+ *
+ * Handles the /remind command by creating a reminder for the current user.
+ */
+public class RemindExpression implements Expression {
+
+    private String reminderText;
+
+    public RemindExpression(String reminderText) {
+        this.reminderText = reminderText;
+    }
+
+    @Override
+    public void interpret(ChatContext chatContext) {
+        System.out.println("[Remind] Reminder created for "
+                + chatContext.getCurrentUser() + ": " + reminderText);
+    }
+}