Add GenericMessageEvent#getThreadChannel() (#1924)

src/main/java/net/dv8tion/jda/api/events/message/GenericMessageEvent.java

@@ -221,4 +221,39 @@ public PrivateChannel getPrivateChannel()
             throw new IllegalStateException("This message event did not happen in a private channel");
         return (PrivateChannel) channel;
     }
+
+    /**
+     * The {@link net.dv8tion.jda.api.entities.ThreadChannel ThreadChannel} the Message was received in.
+     * <br>If this Message was not received in a {@link net.dv8tion.jda.api.entities.ThreadChannel ThreadChannel},
+     * this will throw an {@link java.lang.IllegalStateException}.
+     *
+     * @throws java.lang.IllegalStateException
+     *         If this was not sent in a {@link net.dv8tion.jda.api.entities.ThreadChannel}.
+     *
+     * @return The ThreadChannel the Message was received in
+     *
+     * @see    #isFromGuild()
+     * @see    #isFromType(ChannelType)
+     * @see    #getChannelType()
+     * @see    #isFromThread()
+     */
+    @Nonnull
+    public ThreadChannel getThreadChannel()
+    {
+        if (!isFromThread())
+            throw new IllegalStateException("This message event did not happen in a thread channel");
+        return (ThreadChannel) channel;
+    }
+
+    /**
+     * If the message event was from a {@link net.dv8tion.jda.api.entities.ThreadChannel ThreadChannel}
+     *
+     * @return If the message event was from a ThreadChannel
+     *
+     * @see ChannelType#isThread()
+     */
+    public boolean isFromThread()
+    {
+        return getChannelType().isThread();
+    }
 }