[4/6] beam git commit: Re-add AtomicCoder

[tg...@apache.org]

Re-add AtomicCoder

This is a moderately useful base class for coders which take no
configuration.


Project: http://git-wip-us.apache.org/repos/asf/beam/repo
Commit: http://git-wip-us.apache.org/repos/asf/beam/commit/655947b5
Tree: http://git-wip-us.apache.org/repos/asf/beam/tree/655947b5
Diff: http://git-wip-us.apache.org/repos/asf/beam/diff/655947b5

Branch: refs/heads/master
Commit: 655947b597972d9fd6e1d3a777970b0b1152fa05
Parents: 86a9499
Author: Thomas Groh <tg...@google.com>
Authored: Fri May 5 10:08:32 2017 -0700
Committer: Thomas Groh <tg...@google.com>
Committed: Fri May 5 13:30:51 2017 -0700

----------------------------------------------------------------------
 .../org/apache/beam/sdk/coders/AtomicCoder.java | 86 ++++++++++++++++++++
 1 file changed, 86 insertions(+)
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http://git-wip-us.apache.org/repos/asf/beam/blob/655947b5/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/AtomicCoder.java
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diff --git a/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/AtomicCoder.java b/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/AtomicCoder.java
new file mode 100644
index 0000000..528cfb0
--- /dev/null
+++ b/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/AtomicCoder.java
@@ -0,0 +1,86 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+package org.apache.beam.sdk.coders;
+
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * A {@link Coder} that has no component {@link Coder Coders} or other state.
+ *
+ * <p>Note that, unless the behavior is overridden, atomic coders are presumed to be deterministic.
+ *
+ * <p>All atomic coders of the same class are considered to be equal to each other. As a result,
+ * an {@link AtomicCoder} should have no associated state.
+ *
+ * @param <T> the type of the values being transcoded
+ */
+public abstract class AtomicCoder<T> extends StructuredCoder<T> {
+  /**
+   * Returns an empty list.
+   *
+   * <p>{@link CoderFactories#fromStaticMethods(Class)} builds a {@link CoderFactory} from the
+   * {@code #of()} method and this method, used to determine the components of an object. Because
+   * {@link AtomicCoder} has no components, always returns an empty list.
+   *
+   * @param exampleValue unused, but part of the latent interface expected by {@link
+   *     CoderFactories#fromStaticMethods}
+   */
+  public static <T> List<Object> getInstanceComponents(T exampleValue) {
+    return Collections.emptyList();
+  }
+
+  /**
+   * {@inheritDoc}.
+   *
+   * @throws NonDeterministicException
+   */
+  @Override
+  public void verifyDeterministic() throws NonDeterministicException {}
+
+  @Override
+  public List<? extends Coder<?>> getCoderArguments() {
+    return null;
+  }
+
+  /**
+   * {@inheritDoc}.
+   *
+   * @return the empty {@link List}.
+   */
+  @Override
+  public final List<? extends Coder<?>> getComponents() {
+    return Collections.emptyList();
+  }
+
+  /**
+   * {@inheritDoc}.
+   *
+   * @return true if the other object has the same class as this {@link AtomicCoder}.
+   */
+  @Override
+  public final boolean equals(Object other) {
+    return other != null && this.getClass().equals(other.getClass());
+  }
+
+  @Override
+  public final int hashCode() {
+    return this.getClass().hashCode();
+  }
+}