reformat and clean the code
add an empty test
add print
add print method
modify exception message
revise the code based on the comments from Sam

Add more detailed, helpful comments, parametrize the error message and
delete the repetitious code
revised the comments
add constant fields in JSONConstant
Add a new exception
add comments and get method in JSONObject
add comments and isEqual method in JSONConstant
add a citation file
add comments and modify the javadoc
change the name of toString method
create a basic ui
modify the parseStr
add comments and javadoc