feat: Java SDK feature flags

contents/docs/integrate/_snippets/install-java.mdx

@@ -34,11 +34,16 @@ See the [com.posthog.java](https://search.maven.org/artifact/com.posthog.java/po
 import com.posthog.java.PostHog;
 
 class Sample {
-  private static final String POSTHOG_API_KEY = "<ph_project_api_key>";
+  private static final String POSTHOG_PROJECT_API_KEY = "<ph_project_api_key>";
   private static final String POSTHOG_HOST = "<ph_client_api_host>";
+  // Optional, but required for feature flags
+  private static final String POSTHOG_PERSONAL_API_KEY = "<ph_personal_api_key>";
 
   public static void main(String args[]) {
-    PostHog posthog = new PostHog.Builder(POSTHOG_API_KEY).host(POSTHOG_HOST).build();
+    PostHog posthog = new PostHog.Builder(POSTHOG_PROJECT_API_KEY)
+      .host(POSTHOG_HOST)
+      .personalApiKey(POSTHOG_PERSONAL_API_KEY) // Required for feature flags
+      .build();
 
     // run commands
 

contents/docs/integrate/feature-flags-code/_snippets/feature-flags-code-java.mdx

@@ -0,0 +1,41 @@
+There are 2 steps to implement feature flags in Java:
+
+### Step 1: Evaluate the feature flag value
+
+#### Boolean feature flags
+
+```java
+boolean isMyFlagEnabled = posthog.isFeatureFlagEnabled("flag-key", "distinct_id_of_your_user");
+
+if isMyFlagEnabled == true {
+    // Do something differently for this user
+}
+```
+
+#### Multivariate feature flags
+
+```java
+Optional<String> variant = posthog.getFeatureFlagVariant("flag-key", "distinct_id_of_your_user");
+
+if (variant.isPresent() && variant.get().equals("variant-key")) { // replace 'variant-key' with the key of your variant
+    // Do something differently for this user
+}
+```
+
+import IncludePropertyInEvents from "./include-feature-flag-property-in-backend-events.mdx" 
+
+<IncludePropertyInEvents />
+
+There are two methods you can use to include feature flag information in your events:
+
+#### Include the `$feature/feature_flag_name` property
+
+ In the event properties, include `$feature/feature_flag_name: variant_key`:
+
+```java
+posthog.capture("distinct_id_of_your_user", "event_name", new HashMap<String, Object>() {
+  {
+    put("$feature/feature-flag-key", "variant-key"); // replace feature-flag-key with your flag key. Replace 'variant-key' with the key of your variant
+  }
+});
+```

contents/docs/libraries/java/index.mdx

@@ -11,7 +11,7 @@ features:
   userIdentification: true
   autoCapture: false
   sessionRecording: false
-  featureFlags: false
+  featureFlags: true
   groupAnalytics: true
 ---
 
@@ -79,4 +79,30 @@ import FeatureFlagsLibsIntro from "../_snippets/feature-flags-libs-intro.mdx"
 
 <FeatureFlagsLibsIntro />
 
-Feature flags are not supported yet in our Java SDK. However, you can integrate them into your project by using the [PostHog API](/docs/feature-flags/adding-feature-flag-code?tab=api).
+import JavaFeatureFlagsCode from '../../integrate/feature-flags-code/_snippets/feature-flags-code-java.mdx'
+
+<JavaFeatureFlagsCode />
+
+import LocalEvaluationIntro from "../../feature-flags/snippets/local-evaluation-intro.mdx"
+
+### Local Evaluation
+
+<LocalEvaluationIntro />
+
+For details on how to implement local evaluation, see our [local evaluation guide](/docs/feature-flags/local-evaluation).
+
+## Experiments (A/B tests)
+
+Since [experiments](/docs/experiments/manual) use feature flags, the code for running an experiment is very similar to the feature flags code:
+
+
+```java
+Optional<String> variant = posthog.getFeatureFlagVariant("experimentfeature-flag-name", "user_distinct_id");
+
+if (variant.isPresent() && variant.get().equals("variant-key")) {
+    // Do something differently for this user
+}
+```
+
+It's also possible to [run experiments without using feature flags](/docs/experiments/running-experiments-without-feature-flags).
+