Merge pull request #1 from DandanWang/testing_merge

Testing merge
Updated MainActivity.java
Clear the input editText after pressing the send button.
Merge pull request #2 from DandanWang/testing_cleartext

Updated MainActivity.java
Updated MainActivity.java
Change the file so the application now do not appending message when the
send button is pressed.
Updated MainActivity.java
Added comments for the onClick listener of showExpression button.
Merge pull request #3 from DandanWang/showExpress_comment

Updated MainActivity.java