Remove functional interfaces (#3165)

clients/java/signalr/src/main/java/com/microsoft/signalr/Action.java

@@ -6,7 +6,8 @@ package com.microsoft.signalr;
 /**
  * A callback that takes no parameters.
  */
-@FunctionalInterface
 public interface Action {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke();
 }

clients/java/signalr/src/main/java/com/microsoft/signalr/Action1.java

@@ -8,7 +8,8 @@ package com.microsoft.signalr;
  *
  * @param <T1> The type of the first parameter to the callback.
  */
-@FunctionalInterface
 public interface Action1<T1> {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke(T1 param1);
 }

clients/java/signalr/src/main/java/com/microsoft/signalr/Action2.java

@@ -9,7 +9,8 @@ package com.microsoft.signalr;
  * @param <T1> The type of the first parameter to the callback.
  * @param <T2> The type of the second parameter to the callback.
  */
-@FunctionalInterface
 public interface Action2<T1, T2> {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke(T1 param1, T2 param2);
 }

clients/java/signalr/src/main/java/com/microsoft/signalr/Action3.java

@@ -10,7 +10,8 @@ package com.microsoft.signalr;
  * @param <T2> The type of the second parameter to the callback.
  * @param <T3> The type of the third parameter to the callback.
  */
-@FunctionalInterface
 public interface Action3<T1, T2, T3> {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke(T1 param1, T2 param2, T3 param3);
 }

clients/java/signalr/src/main/java/com/microsoft/signalr/Action4.java

@@ -11,7 +11,8 @@ package com.microsoft.signalr;
  * @param <T3> The type of the third parameter to the callback.
  * @param <T4> The type of the fourth parameter to the callback.
  */
-@FunctionalInterface
 public interface Action4<T1, T2, T3, T4> {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke(T1 param1, T2 param2, T3 param3, T4 param4);
 }

clients/java/signalr/src/main/java/com/microsoft/signalr/Action5.java

@@ -12,7 +12,8 @@ package com.microsoft.signalr;
  * @param <T4> The type of the fourth parameter to the callback.
  * @param <T5> The type of the fifth parameter to the callback.
  */
-@FunctionalInterface
 public interface Action5<T1, T2, T3, T4, T5> {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke(T1 param1, T2 param2, T3 param3, T4 param4, T5 param5);
 }

clients/java/signalr/src/main/java/com/microsoft/signalr/Action6.java

@@ -13,7 +13,8 @@ package com.microsoft.signalr;
  * @param <T5> The type of the fifth parameter to the callback.
  * @param <T6> The type of the sixth parameter to the callback.
  */
-@FunctionalInterface
 public interface Action6<T1, T2, T3, T4, T5, T6> {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke(T1 param1, T2 param2, T3 param3, T4 param4, T5 param5, T6 param6);
 }

clients/java/signalr/src/main/java/com/microsoft/signalr/Action7.java

@@ -14,7 +14,8 @@ package com.microsoft.signalr;
  * @param <T6> The type of the sixth parameter to the callback.
  * @param <T7> The type of the seventh parameter to the callback.
  */
-@FunctionalInterface
 public interface Action7<T1, T2, T3, T4, T5, T6, T7> {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke(T1 param1, T2 param2, T3 param3, T4 param4, T5 param5, T6 param6, T7 param7);
 }

clients/java/signalr/src/main/java/com/microsoft/signalr/Action8.java

@@ -15,7 +15,8 @@ package com.microsoft.signalr;
  * @param <T7> The type of the seventh parameter to the callback.
  * @param <T8> The type of the eighth parameter to the callback.
  */
-@FunctionalInterface
 public interface Action8<T1, T2, T3, T4, T5, T6, T7, T8> {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke(T1 param1, T2 param2, T3 param3, T4 param4, T5 param5, T6 param6, T7 param7, T8 param8);
 }

clients/java/signalr/src/main/java/com/microsoft/signalr/ActionBase.java

@@ -3,7 +3,8 @@
 
 package com.microsoft.signalr;
 
-@FunctionalInterface
 interface ActionBase {
+    // We can't use the @FunctionalInterface annotation because it's only
+    // available on Android API Level 24 and above.
     void invoke(Object ... params);
 }