Reimplement the 'single' operator

Author: zsxwing

rxjava-core/src/main/java/rx/Observable.java

@@ -86,7 +86,7 @@
 import rx.operators.OperationReplay;
 import rx.operators.OperationSample;
 import rx.operators.OperationSequenceEqual;
-import rx.operators.OperationSingle;
+import rx.operators.OperatorSingle;
 import rx.operators.OperationSkip;
 import rx.operators.OperationSkipLast;
 import rx.operators.OperationSkipUntil;
@@ -6216,7 +6216,7 @@ public final Observable<T> serialize() {
      * @see "MSDN: Observable.singleAsync()"
      */
     public final Observable<T> single() {
-        return create(OperationSingle.<T> single(this));
+        return lift(new OperatorSingle<T>());
     }
 
     /**
@@ -6257,7 +6257,7 @@ public final Observable<T> single(Func1<? super T, Boolean> predicate) {
      * @see "MSDN: Observable.singleOrDefaultAsync()"
      */
     public final Observable<T> singleOrDefault(T defaultValue) {
-        return create(OperationSingle.<T> singleOrDefault(this, defaultValue));
+        return lift(new OperatorSingle<T>(defaultValue));
     }
 
     /**

rxjava-core/src/main/java/rx/operators/OperationSingle.java

@@ -0,0 +1,90 @@
+/**
+ * Copyright 2014 Netflix, Inc.
+ * 
+ * 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.operators;
+
+import rx.Observable.Operator;
+import rx.Subscriber;
+
+/**
+ * If the Observable completes after emitting a single item that matches a
+ * predicate, return an Observable containing that item. If it emits more than
+ * one such item or no item, throw an IllegalArgumentException.
+ */
+public final class OperatorSingle<T> implements Operator<T, T> {
+
+    private final boolean hasDefaultValue;
+    private final T defaultValue;
+
+    public OperatorSingle() {
+        this(false, null);
+    }
+
+    public OperatorSingle(T defaultValue) {
+        this(true, defaultValue);
+    }
+
+    private OperatorSingle(boolean hasDefaultValue, final T defaultValue) {
+        this.hasDefaultValue = hasDefaultValue;
+        this.defaultValue = defaultValue;
+    }
+
+    @Override
+    public Subscriber<? super T> call(final Subscriber<? super T> subscriber) {
+        return new Subscriber<T>(subscriber) {
+
+            private T value;
+            private boolean isNonEmpty = false;
+            private boolean hasTooManyElemenets = false;
+
+            @Override
+            public void onNext(T value) {
+                if (isNonEmpty) {
+                    hasTooManyElemenets = true;
+                    subscriber.onError(new IllegalArgumentException("Sequence contains too many elements"));
+                } else {
+                    this.value = value;
+                    isNonEmpty = true;
+                }
+            }
+
+            @Override
+            public void onCompleted() {
+                if (hasTooManyElemenets) {
+                    // We has already sent an onError message
+                } else {
+                    if (isNonEmpty) {
+                        subscriber.onNext(value);
+                        subscriber.onCompleted();
+                    } else {
+                        if (hasDefaultValue) {
+                            subscriber.onNext(defaultValue);
+                            subscriber.onCompleted();
+                        } else {
+                            subscriber.onError(new IllegalArgumentException("Sequence contains no elements"));
+                        }
+                    }
+                }
+            }
+
+            @Override
+            public void onError(Throwable e) {
+                subscriber.onError(e);
+            }
+
+        };
+    }
+
+}

rxjava-core/src/main/java/rx/operators/OperatorSingle.java

@@ -25,7 +25,7 @@
 import rx.Observer;
 import rx.functions.Func1;
 
-public class OperationSingleTest {
+public class OperatorSingleTest {
 
     @Test
     public void testSingle() {