diff --git a/build.gradle b/build.gradle
index d291040e..ce4b945a 100644
--- a/build.gradle
+++ b/build.gradle
@@ -10,9 +10,9 @@ plugins {
 }
 
 compileJava {
-    if (JavaVersion.current().ordinal() > JavaVersion.VERSION_1_8.ordinal()) {
-        options.compilerArgs.addAll(['--release', '8', '-Xlint'])
-    }
+    sourceCompatibility = '8'
+    targetCompatibility = '8'
+    options.compilerArgs.add('-Xlint')
 }
 
 repositories {
diff --git a/src/test/scala/tlschannel/ApiTest.java b/src/test/scala/tlschannel/ApiTest.java
new file mode 100644
index 00000000..2dc7822b
--- /dev/null
+++ b/src/test/scala/tlschannel/ApiTest.java
@@ -0,0 +1,66 @@
+package tlschannel;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.channels.Channels;
+import java.nio.channels.ReadableByteChannel;
+import java.nio.channels.WritableByteChannel;
+import java.security.NoSuchAlgorithmException;
+import java.util.Optional;
+import javax.net.ssl.SSLContext;
+import javax.net.ssl.SSLEngine;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInstance;
+import org.junit.jupiter.api.TestInstance.Lifecycle;
+import tlschannel.impl.ByteBufferSet;
+import tlschannel.impl.TlsChannelImpl;
+
+@TestInstance(Lifecycle.PER_CLASS)
+public class ApiTest {
+
+    private static final int arraySize = 1024;
+
+    private final ReadableByteChannel readChannel = Channels.newChannel(new ByteArrayInputStream(new byte[arraySize]));
+    private final WritableByteChannel writeChannel = Channels.newChannel(new ByteArrayOutputStream(arraySize));
+
+    private TlsChannelImpl newSocket() {
+        try {
+            SSLEngine sslEngine = SSLContext.getDefault().createSSLEngine();
+            return new TlsChannelImpl(
+                    readChannel,
+                    writeChannel,
+                    sslEngine,
+                    Optional.empty(),
+                    session -> {},
+                    true,
+                    new TrackingAllocator(new HeapBufferAllocator()),
+                    new TrackingAllocator(new HeapBufferAllocator()),
+                    true /* releaseBuffers */,
+                    false /* waitForCloseConfirmation */);
+        } catch (NoSuchAlgorithmException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Test
+    public void testReadIntoReadOnlyBuffer() throws IOException {
+        try (TlsChannelImpl socket = newSocket()) {
+            Assertions.assertThrows(IllegalArgumentException.class, () -> {
+                socket.read(new ByteBufferSet(ByteBuffer.allocate(1).asReadOnlyBuffer()));
+            });
+        }
+    }
+
+    @Test
+    public void testReadIntoBufferWithoutCapacity() throws IOException {
+        try (TlsChannelImpl socket = newSocket()) {
+            Assertions.assertEquals(
+                    0,
+                    socket.read(new ByteBufferSet(ByteBuffer.allocate(0))),
+                    "read must return zero when the buffer was empty");
+        }
+    }
+}
diff --git a/src/test/scala/tlschannel/ApiTest.scala b/src/test/scala/tlschannel/ApiTest.scala
deleted file mode 100644
index a35ad173..00000000
--- a/src/test/scala/tlschannel/ApiTest.scala
+++ /dev/null
@@ -1,58 +0,0 @@
-package tlschannel
-
-import org.junit.jupiter.api.TestInstance.Lifecycle
-import org.junit.jupiter.api.{Assertions, Test, TestInstance}
-
-import java.nio.channels.Channels
-import java.io.ByteArrayInputStream
-import java.io.ByteArrayOutputStream
-import java.nio.ByteBuffer
-import javax.net.ssl.SSLContext
-import tlschannel.impl.{BufferHolder, ByteBufferSet, TlsChannelImpl}
-
-import java.util.Optional
-
-@TestInstance(Lifecycle.PER_CLASS)
-class ApiTest {
-
-  val arraySize = 1024
-
-  val readChannel = Channels.newChannel(new ByteArrayInputStream(new Array(arraySize)))
-  val writeChannel = Channels.newChannel(new ByteArrayOutputStream(arraySize))
-
-  def newSocket() = {
-    val sslEngine = SSLContext.getDefault.createSSLEngine
-    new TlsChannelImpl(
-      readChannel,
-      writeChannel,
-      sslEngine,
-      Optional.empty[BufferHolder],
-      _ => (),
-      true,
-      new TrackingAllocator(new HeapBufferAllocator),
-      new TrackingAllocator(new HeapBufferAllocator),
-      true /* releaseBuffers */,
-      false /* waitForCloseConfirmation */
-    )
-  }
-
-  @Test
-  def testReadIntoReadOnlyBuffer(): Unit = {
-    val socket = newSocket()
-    Assertions.assertThrows(
-      classOf[IllegalArgumentException],
-      () => socket.read(new ByteBufferSet(ByteBuffer.allocate(1).asReadOnlyBuffer()))
-    )
-  }
-
-  @Test
-  def testReadIntoBufferWithoutCapacity(): Unit = {
-    val socket = newSocket()
-    Assertions.assertEquals(
-      0,
-      socket.read(new ByteBufferSet(ByteBuffer.allocate(0))),
-      "read must return zero when the buffer was empty"
-    )
-  }
-
-}
diff --git a/src/test/scala/tlschannel/helpers/NullSslEngine.java b/src/test/scala/tlschannel/helpers/NullSslEngine.java
index 76f3519c..5964b73e 100644
--- a/src/test/scala/tlschannel/helpers/NullSslEngine.java
+++ b/src/test/scala/tlschannel/helpers/NullSslEngine.java
@@ -115,7 +115,7 @@ public void setWantClientAuth(boolean b) {}
 
     @Override
     public SSLEngineResult unwrap(ByteBuffer src, ByteBuffer[] dsts, int offset, int length) {
-        var dstSet = new ByteBufferSet(dsts, offset, length);
+        ByteBufferSet dstSet = new ByteBufferSet(dsts, offset, length);
         if (!src.hasRemaining()) {
             return new SSLEngineResult(Status.BUFFER_UNDERFLOW, HandshakeStatus.NOT_HANDSHAKING, 0, 0);
         }
@@ -132,7 +132,7 @@ public SSLEngineResult unwrap(ByteBuffer src, ByteBuffer[] dsts, int offset, int
 
     @Override
     public SSLEngineResult wrap(ByteBuffer[] srcs, int offset, int length, ByteBuffer dst) {
-        var srcSet = new ByteBufferSet(srcs, offset, length);
+        ByteBufferSet srcSet = new ByteBufferSet(srcs, offset, length);
         if (!srcSet.hasRemaining()) {
             return new SSLEngineResult(Status.OK, HandshakeStatus.NOT_HANDSHAKING, 0, 0);
         }