Assignment java stack

1)      If you were to remove an element from a stack, what abnormality would you expect? How would you prevent the program from terminating abnormally?

2)      Given that A, B, C, and D are operands; and *,+,- are operators, convert the following postfix expression to infix expression:

A B + C * D -

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3)      List two applications where the concept of Stack would be appropriate. Give brief reason for each application stated.