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javajspservletsjstlundefined

Why ${flag==Y} returns True and ${flag=='Y'} returns False?

I am confused by below behavior. Variable flag is passed from controller to jsp code:

flag: <c:out value="${requestScope.flag}"/> 
flag eq 'Y': ${requestScope.flag eq 'Y'}
flag == 'Y': ${requestScope.flag=='Y'}
flag==Y: ${requestScope.flag==Y}

Case 1: Flag is not passed to view (output):

flag: 
flag eq 'Y': false 
flag == 'Y': false 
flag==Y: true

Case 2: Flag with value "Y" is passed to view:

flag: Y
flag eq 'Y': true 
flag == 'Y': true 
flag==Y: false
Solution

  • requestScope.flag==Y means compare with variable Y which is undefined

    Thus when flag is sent, undefined variable isn't equal to flag and return false in second case,

    While in first case both are undefined variables, therefore it returns true