Merge pull request ReactiveX#96 from ReactiveX/jw/hide-all-the-things

Hide ViewActions implementation details. Javadoc normalization.

Author: mttkay

rxandroid/src/main/java/rx/android/internal/Preconditions.java

@@ -0,0 +1,39 @@
+/**
+ * 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.
+ */
+package rx.android.internal;
+
+public final class Preconditions {
+    private Preconditions() {
+        throw new AssertionError("No instances");
+    }
+
+    public static <T> T checkNotNull(T value, String message) {
+        if (value == null) {
+            throw new NullPointerException(message);
+        }
+        return value;
+    }
+
+    public static void checkArgument(boolean check, String message) {
+        if (!check) {
+            throw new IllegalArgumentException(message);
+        }
+    }
+
+    public static void checkState(boolean check, String message) {
+        if (!check) {
+            throw new IllegalStateException(message);
+        }
+    }
+}