Add contravariant for min and max

Author: zsxwing

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

@@ -3649,7 +3649,7 @@ public static Observable<Double> averageDoubles(Observable<Double> source) {
      *            if the source is empty
      * @see <a href="http://msdn.microsoft.com/en-us/library/hh229715(v=vs.103).aspx">MSDN: Observable.Min</a>
      */
-    public static <T extends Comparable<T>> Observable<T> min(Observable<T> source) {
+    public static <T extends Comparable<? super T>> Observable<T> min(Observable<T> source) {
         return OperationMinMax.min(source);
     }
 
@@ -3665,7 +3665,7 @@ public static <T extends Comparable<T>> Observable<T> min(Observable<T> source)
      *            if the source is empty
      * @see <a href="http://msdn.microsoft.com/en-us/library/hh229095(v=vs.103).aspx">MSDN: Observable.Min</a>
      */
-    public Observable<T> min(Comparator<T> comparator) {
+    public Observable<T> min(Comparator<? super T> comparator) {
         return OperationMinMax.min(this, comparator);
     }
 
@@ -3678,7 +3678,7 @@ public Observable<T> min(Comparator<T> comparator) {
      * @return an observable emitting a List of the elements with the minimum key value.
      * @see <a href="http://msdn.microsoft.com/en-us/library/hh228970(v=vs.103).aspx">MSDN: Observable.MinBy</a>
      */
-    public <R extends Comparable<R>> Observable<List<T>> minBy(Func1<T, R> selector) {
+    public <R extends Comparable<? super R>> Observable<List<T>> minBy(Func1<T, R> selector) {
         return OperationMinMax.minBy(this, selector);
     }
 
@@ -3693,7 +3693,7 @@ public <R extends Comparable<R>> Observable<List<T>> minBy(Func1<T, R> selector)
      * @return an observable emitting a List of the elements with the minimum key value  according to the specified comparator.
      * @see <a href="http://msdn.microsoft.com/en-us/library/hh228970(v=vs.103).aspx">MSDN: Observable.MinBy</a>
      */
-    public <R> Observable<List<T>> minBy(Func1<T, R> selector, Comparator<R> comparator) {
+    public <R> Observable<List<T>> minBy(Func1<T, R> selector, Comparator<? super R> comparator) {
         return OperationMinMax.minBy(this, selector, comparator);
     }
 
@@ -3709,7 +3709,7 @@ public <R> Observable<List<T>> minBy(Func1<T, R> selector, Comparator<R> compara
      *            if the source is empty.
      * @see <a href="http://msdn.microsoft.com/en-us/library/hh211837(v=vs.103).aspx">MSDN: Observable.Max</a>
      */
-    public static <T extends Comparable<T>> Observable<T> max(Observable<T> source) {
+    public static <T extends Comparable<? super T>> Observable<T> max(Observable<T> source) {
         return OperationMinMax.max(source);
     }
 
@@ -3725,7 +3725,7 @@ public static <T extends Comparable<T>> Observable<T> max(Observable<T> source)
      *            if the source is empty.
      * @see <a href="http://msdn.microsoft.com/en-us/library/hh211635(v=vs.103).aspx">MSDN: Observable.Max</a>
      */
-    public Observable<T> max(Comparator<T> comparator) {
+    public Observable<T> max(Comparator<? super T> comparator) {
         return OperationMinMax.max(this, comparator);
     }
 
@@ -3738,7 +3738,7 @@ public Observable<T> max(Comparator<T> comparator) {
      * @return an observable emitting a List of the elements with the maximum key value.
      * @see <a href="http://msdn.microsoft.com/en-us/library/hh229058(v=vs.103).aspx">MSDN: Observable.MaxBy</a>
      */
-    public <R extends Comparable<R>> Observable<List<T>> maxBy(Func1<T, R> selector) {
+    public <R extends Comparable<? super R>> Observable<List<T>> maxBy(Func1<T, R> selector) {
         return OperationMinMax.maxBy(this, selector);
     }
 
@@ -3753,7 +3753,7 @@ public <R extends Comparable<R>> Observable<List<T>> maxBy(Func1<T, R> selector)
      * @return an observable emitting a List of the elements with the maximum key value  according to the specified comparator.
      * @see <a href="http://msdn.microsoft.com/en-us/library/hh244330(v=vs.103).aspx">MSDN: Observable.MaxBy</a>
      */
-    public <R> Observable<List<T>> maxBy(Func1<T, R> selector, Comparator<R> comparator) {
+    public <R> Observable<List<T>> maxBy(Func1<T, R> selector, Comparator<? super R> comparator) {
         return OperationMinMax.maxBy(this, selector, comparator);
     }
 

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

@@ -28,47 +28,47 @@
  */
 public class OperationMinMax {
 
-    public static <T extends Comparable<T>> Observable<T> min(
+    public static <T extends Comparable<? super T>> Observable<T> min(
             Observable<T> source) {
         return minMax(source, -1L);
     }
 
     public static <T> Observable<T> min(Observable<T> source,
-            final Comparator<T> comparator) {
+            final Comparator<? super T> comparator) {
         return minMax(source, comparator, -1L);
     }
 
-    public static <T, R extends Comparable<R>> Observable<List<T>> minBy(
+    public static <T, R extends Comparable<? super R>> Observable<List<T>> minBy(
             Observable<T> source, final Func1<T, R> selector) {
         return minMaxBy(source, selector, -1L);
     }
 
     public static <T, R> Observable<List<T>> minBy(Observable<T> source,
-            final Func1<T, R> selector, final Comparator<R> comparator) {
+            final Func1<T, R> selector, final Comparator<? super R> comparator) {
         return minMaxBy(source, selector, comparator, -1L);
     }
 
-    public static <T extends Comparable<T>> Observable<T> max(
+    public static <T extends Comparable<? super T>> Observable<T> max(
             Observable<T> source) {
         return minMax(source, 1L);
     }
 
     public static <T> Observable<T> max(Observable<T> source,
-            final Comparator<T> comparator) {
+            final Comparator<? super T> comparator) {
         return minMax(source, comparator, 1L);
     }
 
-    public static <T, R extends Comparable<R>> Observable<List<T>> maxBy(
+    public static <T, R extends Comparable<? super R>> Observable<List<T>> maxBy(
             Observable<T> source, final Func1<T, R> selector) {
         return minMaxBy(source, selector, 1L);
     }
 
     public static <T, R> Observable<List<T>> maxBy(Observable<T> source,
-            final Func1<T, R> selector, final Comparator<R> comparator) {
+            final Func1<T, R> selector, final Comparator<? super R> comparator) {
         return minMaxBy(source, selector, comparator, 1L);
     }
 
-    private static <T extends Comparable<T>> Observable<T> minMax(
+    private static <T extends Comparable<? super T>> Observable<T> minMax(
             Observable<T> source, final long flag) {
         return source.reduce(new Func2<T, T, T>() {
             @Override
@@ -82,7 +82,7 @@ public T call(T acc, T value) {
     }
 
     private static <T> Observable<T> minMax(Observable<T> source,
-            final Comparator<T> comparator, final long flag) {
+            final Comparator<? super T> comparator, final long flag) {
         return source.reduce(new Func2<T, T, T>() {
             @Override
             public T call(T acc, T value) {
@@ -94,7 +94,7 @@ public T call(T acc, T value) {
         });
     }
 
-    private static <T, R extends Comparable<R>> Observable<List<T>> minMaxBy(
+    private static <T, R extends Comparable<? super R>> Observable<List<T>> minMaxBy(
             Observable<T> source, final Func1<T, R> selector, final long flag) {
         return source.reduce(new ArrayList<T>(),
                 new Func2<List<T>, T, List<T>>() {
@@ -119,7 +119,7 @@ public List<T> call(List<T> acc, T value) {
     }
 
     private static <T, R> Observable<List<T>> minMaxBy(Observable<T> source,
-            final Func1<T, R> selector, final Comparator<R> comparator,
+            final Func1<T, R> selector, final Comparator<? super R> comparator,
             final long flag) {
         return source.reduce(new ArrayList<T>(),
                 new Func2<List<T>, T, List<T>>() {