simple sorting server Java -- 2

The sorting server operates a stack and clients push values and operations on to the stack. While, usually, each client should have its own stack, you may use a single stack on the server. You may also assume that operations are always sensible: that is, we will only push an operator after pushing at least on value and we will only pop when there is a value on the stack. You may also assume that the operator provided will only be one of the four displayed types and that the values are always integers.