Needs some compatability code for missing features in Android.

src/main/java/zmq/util/function/BiConsumer.java

@@ -0,0 +1,23 @@
+package zmq.util.function;
+
+/**
+ Represents an operation that accepts two input arguments and returns no result. This is the two-arity specialization of Consumer.
+ Unlike most other functional interfaces, {@link BiConsumer} is expected to operate via side-effects.
+
+ *
+ * <p>This is a functional interface
+ * whose functional method is {@link #accept(Object, Object)}.
+ *
+ * @param <T> the type of the input to the operation
+ *
+ */
+public interface BiConsumer<T, U>
+{
+    /**
+     * Performs this operation on the given argument.
+     *
+     * @param t the first input argument
+     * @param t the second input argument
+     */
+    void accept(T t, U u);
+}

src/main/java/zmq/util/function/Optional.java

@@ -0,0 +1,23 @@
+package zmq.util.function;
+
+public class Optional<T>
+{
+    private final T value;
+
+    private Optional(T value)
+    {
+        this.value = value;
+    }
+
+    public void ifPresent(Consumer<T> consumer)
+    {
+        if (value != null) {
+            consumer.accept(value);
+        }
+    }
+
+    public static <T> Optional<T> ofNullable(T value)
+    {
+        return new Optional<>(value);
+    }
+}

src/test/java/zmq/io/mechanism/MechanismTester.java

@@ -3,14 +3,10 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.net.Socket;
-import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
-import java.util.function.BiFunction;
-import java.util.function.Consumer;
-import java.util.function.Function;
 
 import zmq.Ctx;
 import zmq.Helper;
@@ -19,6 +15,10 @@
 import zmq.SocketBase;
 import zmq.ZMQ;
 import zmq.util.TestUtils;
+import zmq.util.function.BiFunction;
+import zmq.util.function.Function;
+import zmq.util.function.Consumer;
+import zmq.util.function.Optional;
 
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.notNullValue;

src/test/java/zmq/io/mechanism/SecurityCurveTest.java

@@ -1,14 +1,14 @@
 package zmq.io.mechanism;
 
 import java.util.concurrent.CompletableFuture;
-import java.util.function.BiFunction;
-import java.util.function.Function;
 
 import org.junit.Test;
 
 import zmq.SocketBase;
 import zmq.ZMQ;
 import zmq.io.mechanism.curve.Curve;
+import zmq.util.function.BiFunction;
+import zmq.util.function.Function;
 
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.nullValue;

src/test/java/zmq/io/mechanism/SecurityNullTest.java

@@ -1,13 +1,13 @@
 package zmq.io.mechanism;
 
 import java.util.concurrent.CompletableFuture;
-import java.util.function.BiFunction;
-import java.util.function.Function;
 
 import org.junit.Test;
 
 import zmq.SocketBase;
 import zmq.ZMQ;
+import zmq.util.function.BiFunction;
+import zmq.util.function.Function;
 
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.nullValue;

src/test/java/zmq/io/mechanism/SecurityPlainTest.java

@@ -1,13 +1,13 @@
 package zmq.io.mechanism;
 
 import java.util.concurrent.CompletableFuture;
-import java.util.function.BiFunction;
-import java.util.function.Function;
 
 import org.junit.Test;
 
 import zmq.SocketBase;
 import zmq.ZMQ;
+import zmq.util.function.BiFunction;
+import zmq.util.function.Function;
 
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.nullValue;