Sync Factory Method, Abstract Factory, Builder, Prototype to Java 25; fix post/code mismatches

01-creational/builder/HttpRequest.java

@@ -0,0 +1,76 @@
+package builder;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+
+public final class HttpRequest {
+
+    // All fields are final: the object is immutable after build() returns.
+    private final String url;
+    private final String method;
+    private final String body;
+    private final Map<String, String> headers;
+    private final int timeoutMs;
+    private final int maxRetries;
+
+    // Private: the only path to an HttpRequest is through Builder.build()
+    private HttpRequest(Builder builder) {
+        this.url        = Objects.requireNonNull(builder.url, "URL is required");
+        this.method     = builder.method;
+        this.body       = builder.body;
+        this.headers    = Collections.unmodifiableMap(new HashMap<>(builder.headers));
+        this.timeoutMs  = builder.timeoutMs;
+        this.maxRetries = builder.maxRetries;
+    }
+
+    // Getters only — no setters, enforcing immutability
+    public String getUrl()          { return url; }
+    public String getMethod()       { return method; }
+    public String getBody()         { return body; }
+    public Map<String, String> getHeaders() { return headers; }
+    public int getTimeoutMs()       { return timeoutMs; }
+    public int getMaxRetries()      { return maxRetries; }
+
+    @Override
+    public String toString() {
+        return String.format("%s %s (timeout=%dms, retries=%d, headers=%s, body=%s)",
+            method, url, timeoutMs, maxRetries, headers, body);
+    }
+
+    // -----------------------------------------------------------------------
+    // THE BUILDER — static inner class so it can call the private constructor
+    // -----------------------------------------------------------------------
+    public static class Builder {
+
+        // Required field — no default, must be set
+        private String url;
+
+        // Optional fields with sensible defaults
+        private String method     = "GET";
+        private String body       = null;
+        private Map<String, String> headers = new HashMap<>();
+        private int timeoutMs     = 30_000;  // 30 seconds
+        private int maxRetries    = 0;
+
+        // Fluent methods: each returns 'this' so calls can be chained
+        public Builder url(String url)              { this.url = url; return this; }
+        public Builder method(String method)        { this.method = method; return this; }
+        public Builder body(String body)            { this.body = body; return this; }
+        public Builder header(String key, String v) { headers.put(key, v); return this; }
+        public Builder timeoutMs(int ms)            { this.timeoutMs = ms; return this; }
+        public Builder maxRetries(int n)            { this.maxRetries = n; return this; }
+
+        // Terminal method: validates and creates the immutable HttpRequest
+        public HttpRequest build() {
+            if (url == null || url.isBlank()) {
+                throw new IllegalStateException("url() is required before calling build()");
+            }
+            if (maxRetries < 0) {
+                throw new IllegalStateException("maxRetries must be >= 0");
+            }
+            return new HttpRequest(this);  // calls the private constructor
+        }
+    }
+}