[samples]: Samples using the Java API.

samples/java/training/pom.xml

+<project>
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>org.myorg</groupId>
+    <artifactId>training</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <properties>
+      <exec.mainClass>Train</exec.mainClass>
+      <!-- The sample code requires at least JDK 1.7. -->
+      <!-- The maven compiler plugin defaults to a lower version -->
+      <maven.compiler.source>1.7</maven.compiler.source>
+      <maven.compiler.target>1.7</maven.compiler.target>
+    </properties>
+    <dependencies>
+      <dependency>
+        <groupId>org.tensorflow</groupId>
+        <artifactId>tensorflow</artifactId>
+        <version>1.4.0</version>
+      </dependency>
+    </dependencies>
+</project>

samples/java/training/src/main/java/Train.java

+/* Copyright 2018 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.List;
+import java.util.Random;
+import org.tensorflow.Graph;
+import org.tensorflow.Session;
+import org.tensorflow.Tensor;
+import org.tensorflow.Tensors;
+
+/**
+ * Training a trivial linear model.
+ */
+public class Train {
+  public static void main(String[] args) throws Exception {
+    if (args.length != 2) {
+      System.err.println("Require two arguments: The GraphDef file and checkpoint directory");
+      System.exit(1);
+    }
+
+    final byte[] graphDef = Files.readAllBytes(Paths.get(args[0]));
+    final String checkpointDir = args[1];
+    final boolean checkpointExists = Files.exists(Paths.get(checkpointDir));
+
+    try (Graph graph = new Graph();
+        Session sess = new Session(graph);
+        Tensor<String> checkpointPrefix =
+            Tensors.create(Paths.get(checkpointDir, "ckpt").toString())) {
+      graph.importGraphDef(graphDef);
+
+      // Initialize or restore
+      if (checkpointExists) {
+        sess.runner().feed("save/Const", checkpointPrefix).addTarget("save/restore_all").run();
+      } else {
+        sess.runner().addTarget("init").run();
+      }
+      System.out.print("Starting from       : ");
+      printVariables(sess);
+
+      // Train a bunch of times.
+      // (Will be much more efficient if we sent batches instead of individual values).
+      final Random r = new Random();
+      final int NUM_EXAMPLES = 500;
+      for (int i = 1; i <= 5; i++) {
+        for (int n = 0; n < NUM_EXAMPLES; n++) {
+          float in = r.nextFloat();
+          try (Tensor<Float> input = Tensors.create(in);
+              Tensor<Float> target = Tensors.create(3 * in + 2)) {
+            sess.runner().feed("input", input).feed("target", target).addTarget("train").run();
+          }
+        }
+        System.out.printf("After %5d examples: ", i*NUM_EXAMPLES);
+        printVariables(sess);
+      }
+
+      // Checkpoint
+      sess.runner().feed("save/Const", checkpointPrefix).addTarget("save/control_dependency").run();
+
+      // Example of "inference" in the same graph:
+      try (Tensor<Float> input = Tensors.create(1.0f);
+          Tensor<Float> output =
+              sess.runner().feed("input", input).fetch("output").run().get(0).expect(Float.class)) {
+        System.out.printf(
+            "For input %f, produced %f (ideally would produce 3*%f + 2)\n",
+            input.floatValue(), output.floatValue(), input.floatValue());
+      }
+    }
+  }
+
+  private static void printVariables(Session sess) {
+    List<Tensor<?>> values = sess.runner().fetch("W/read").fetch("b/read").run();
+    System.out.printf("W = %f\tb = %f\n", values.get(0).floatValue(), values.get(1).floatValue());
+    for (Tensor<?> t : values) {
+      t.close();
+    }
+  }
+}