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

03-behavioral/template-method/CsvMigration.java

@@ -0,0 +1,27 @@
+package template;
+
+public class CsvMigration extends DataMigration {
+
+    private final String filePath;
+
+    public CsvMigration(String filePath) { this.filePath = filePath; }
+
+    @Override protected String getSourceName() { return "CSV:" + filePath; }
+
+    @Override
+    protected void connect() {
+        System.out.println("  Opening CSV file: " + filePath);
+    }
+
+    @Override
+    protected int readData() {
+        System.out.println("  Parsing CSV rows...");
+        return 1_500;  // simulated row count
+    }
+
+    @Override
+    protected int transformData(int rawCount) {
+        System.out.println("  Mapping CSV columns to target schema (" + rawCount + " rows)...");
+        return rawCount;  // no rows lost
+    }
+}