docs: fix inaccuracies in README code examples

Signed-off-by: Jonathan Norris <jonathan.norris@dynatrace.com>

Author: jonathannorris

README.md

@@ -217,15 +217,15 @@ If the flag management system you're using supports targeting, you can provide t
 // set a value to the global context
 OpenFeatureAPI api = OpenFeatureAPI.getInstance();
 Map<String, Value> apiAttrs = new HashMap<>();
-apiAttrs.put("region", new Value(System.getEnv("us-east-1")));
+apiAttrs.put("region", new Value(System.getenv("AWS_REGION")));
 EvaluationContext apiCtx = new ImmutableContext(apiAttrs);
 api.setEvaluationContext(apiCtx);
 
 // set a value to the client context
 Map<String, Value> clientAttrs = new HashMap<>();
-clientAttrs.put("region", new Value(System.getEnv("us-east-1")));
+clientAttrs.put("region", new Value(System.getenv("AWS_REGION")));
 EvaluationContext clientCtx = new ImmutableContext(clientAttrs);
-Client client = api.getInstance().getClient();
+Client client = api.getClient();
 client.setEvaluationContext(clientCtx);
 
 // set a value to the invocation context
@@ -292,7 +292,7 @@ If a domain has no associated provider, the global provider is used.
 FeatureProvider scopedProvider = new MyProvider();
 
 // registering the default provider
-OpenFeatureAPI.getInstance().setProvider(LocalProvider());
+OpenFeatureAPI.getInstance().setProvider(new LocalProvider());
 // registering a provider to a domain
 OpenFeatureAPI.getInstance().setProvider("my-domain", new CachedProvider());
 
@@ -452,25 +452,26 @@ This can be a new repository or included in [the existing contrib repository](ht
 Implement your own hook by conforming to the `Hook interface`.
 
 ```java
-class MyHook implements Hook {
+class MyHook implements Hook<Object> {
 
     @Override
-    public Optional before(HookContext ctx, Map hints) {
+    public Optional<EvaluationContext> before(HookContext<Object> ctx, Map<String, Object> hints) {
         // code that runs before the flag evaluation
+        return Optional.empty();
     }
 
     @Override
-    public void after(HookContext ctx, FlagEvaluationDetails details, Map hints) {
+    public void after(HookContext<Object> ctx, FlagEvaluationDetails<Object> details, Map<String, Object> hints) {
         // code that runs after the flag evaluation succeeds
     }
 
     @Override
-    public void error(HookContext ctx, Exception error, Map hints) {
+    public void error(HookContext<Object> ctx, Exception error, Map<String, Object> hints) {
         // code that runs when there's an error during a flag evaluation
     }
 
     @Override
-    public void finallyAfter(HookContext ctx, FlagEvaluationDetails details, Map hints) {
+    public void finallyAfter(HookContext<Object> ctx, FlagEvaluationDetails<Object> details, Map<String, Object> hints) {
         // code that runs regardless of success or error
     }
 };