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

02-structural/facade/Subsystems.java

@@ -0,0 +1,62 @@
+package facade;
+
+/**
+ * Complex subsystem classes — these are what the Facade hides.
+ * Each class has its own complex API; clients shouldn't need to know all of them.
+ */
+
+class VideoFile {
+    private final String filename;
+    private final String codecType;
+
+    VideoFile(String filename) {
+        this(filename, filename.endsWith(".mp4") ? "mpeg4" : "ogg");
+    }
+
+    VideoFile(String filename, String codec) {
+        this.filename  = filename;
+        this.codecType = codec;
+        System.out.println("  VideoFile: " + filename + " [codec: " + codecType + "]");
+    }
+
+    public String getFilename()  { return filename; }
+    public String getCodecType() { return codecType; }
+}
+
+interface Codec { String getName(); }
+
+class MPEG4CompressionCodec implements Codec {
+    @Override public String getName() { return "mpeg4"; }
+}
+
+class OggCompressionCodec implements Codec {
+    @Override public String getName() { return "ogg"; }
+}
+
+class CodecFactory {
+    static Codec extract(VideoFile file) {
+        System.out.println("  CodecFactory: extracting codec from " + file.getFilename());
+        if ("mpeg4".equals(file.getCodecType())) return new MPEG4CompressionCodec();
+        return new OggCompressionCodec();
+    }
+}
+
+class BitrateReader {
+    static VideoFile read(VideoFile file, Codec codec) {
+        System.out.println("  BitrateReader: reading " + file.getFilename()
+                + " with codec " + codec.getName());
+        return new VideoFile(file.getFilename());
+    }
+
+    static VideoFile convert(VideoFile buffer, Codec codec) {
+        System.out.println("  BitrateReader: converting to " + codec.getName());
+        return new VideoFile(buffer.getFilename());
+    }
+}
+
+class AudioMixer {
+    static VideoFile fix(VideoFile result) {
+        System.out.println("  AudioMixer: fixing audio tracks");
+        return new VideoFile(result.getFilename());
+    }
+}