diff --git a/Config.java b/Config.java
new file mode 100644
index 0000000..703176d
--- /dev/null
+++ b/Config.java
@@ -0,0 +1,134 @@
+/**
+ * Product class: Complex configuration object 
+ * Contains required and optional parameters, created via builder pattern
+ */
+public class Config {
+
+    /**
+     * Builder class for Config
+     */
+    public static class ConfigBuilder {
+
+        /**
+         * Default encoding UTF-8
+         */
+        private String encoding = "UTF-8";
+        /**
+         * Default max connections 10
+         */
+        private int maxConnections = 10;
+        /**
+         * Default timeout 3000ms
+         */
+        private int timeout = 3000;
+        /**
+         * Required parameter (passed in builder constructor)
+         */
+        private final String url;
+
+        /**
+         * Builder constructor: requires mandatory parameter
+         * 
+         * @param url    Target service URL (required)
+         */
+        public ConfigBuilder(String url){
+            this.url = url;
+        }
+
+        /**
+         * Build Config object and validate parameter legality
+         * @return Immutable Config instance
+         */
+        public Config build(){
+            // Validate parameters
+            if (url == null || url.trim().isEmpty()) {
+                throw new IllegalArgumentException("URL cannot be null or empty");
+            }
+            if (maxConnections <= 0) {
+                throw new IllegalArgumentException("Max connections must be positive");
+            }
+            if (timeout <= 0) {
+                throw new IllegalArgumentException("Timeout must be positive");
+            }
+            return new Config(this);
+        }
+
+        /**
+         * Set encoding format (optional parameter)
+         * @return Builder itself (for method chaining)
+         * 
+         * @param encoding    Encoding format (e.g. "GBK")
+         */
+        public ConfigBuilder setEncoding(String encoding){
+            this.encoding = encoding;
+            return this;
+        }
+
+        /**
+         * Set max connections (optional parameter)
+         * @return Builder itself (for method chaining)
+         * 
+         * @param maxConnections    Max connections
+         */
+        public ConfigBuilder setMaxConnections(int maxConnections){
+            this.maxConnections = maxConnections;
+            return this;
+        }
+
+        /**
+         * Set timeout (optional parameter)
+         * @return Builder itself (for method chaining)
+         * 
+         * @param timeout    Timeout in milliseconds
+         */
+        public ConfigBuilder setTimeout(int timeout){
+            this.timeout = timeout;
+            return this;
+        }
+    }
+
+    /**
+     * Optional parameter, demonstrating extensibility
+     */
+    private final String encoding;
+    private final int maxConnections;
+    /**
+     * Optional parameter (has default value, can be modified via builder)
+     */
+    private final int timeout;
+    /**
+     * Required parameter (must be set, no default value)
+     */
+    private final String url;
+
+    /**
+     * Private constructor: only allowed to be called by internal builder
+     * 
+     * @param builder    Builder object providing parameters
+     */
+    private Config(ConfigBuilder builder){
+        this.url = builder.url;
+        this.encoding = builder.encoding;
+        this.maxConnections = builder.maxConnections;
+        this.timeout = builder.timeout;
+    }
+
+    public String getEncoding(){
+        return encoding;
+    }
+
+    public int getMaxConnections(){
+        return maxConnections;
+    }
+
+    public int getTimeout(){
+        return timeout;
+    }
+
+    /**
+     * Getter methods for all parameters (no setters to ensure immutability)
+     */
+    public String getUrl(){
+        return url;
+    }
+}
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