Add all 23 GoF design pattern implementations (2026-06-13)

02-structural/decorator/Main.java

@@ -0,0 +1,53 @@
+package decorator;
+
+/**
+ * Decorator Design Pattern — Runnable Demo
+ *
+ * Shows how text processors can be stacked like Java IO streams.
+ * Each decorator adds one behaviour; the order of wrapping matters.
+ *
+ * Run: javac decorator/*.java && java decorator.Main
+ * Article: https://ankurm.com/decorator-design-pattern-java/
+ */
+public class Main {
+
+    public static void main(String[] args) {
+        System.out.println("=== Decorator Design Pattern Demo ===\n");
+
+        String input = "  hello world, badword is here  ";
+        System.out.println("Input: \"" + input + "\"");
+        System.out.println();
+
+        // Stack 1: just trim
+        TextProcessor trimOnly = new TrimDecorator(new PlainTextProcessor());
+        System.out.println("Trim only:               \"" + trimOnly.process(input) + "\"");
+
+        // Stack 2: trim, then upper case
+        TextProcessor trimThenUpper =
+            new UpperCaseDecorator(
+                new TrimDecorator(
+                    new PlainTextProcessor()));
+        System.out.println("Trim + UpperCase:        \"" + trimThenUpper.process(input) + "\"");
+
+        // Stack 3: trim, filter profanity, then upper case
+        TextProcessor full =
+            new UpperCaseDecorator(
+                new ProfanityFilterDecorator(
+                    new TrimDecorator(
+                        new PlainTextProcessor())));
+        System.out.println("Trim + Filter + Upper:   \"" + full.process(input) + "\"");
+
+        // Stack 4: different order — filter then trim (order matters!)
+        TextProcessor filterFirst =
+            new TrimDecorator(
+                new ProfanityFilterDecorator(
+                    new PlainTextProcessor()));
+        System.out.println("Filter + Trim:           \"" + filterFirst.process(input) + "\"");
+
+        System.out.println();
+        System.out.println("JDK parallel: new BufferedReader(new InputStreamReader(socket.getInputStream()))");
+        System.out.println("Same pattern: each wrapper adds one behaviour, order matters.");
+
+        System.out.println("\n=== Demo complete ===");
+    }
+}