Retrieving current time and computing a hash value
Just a couple of points which are more from a stylistic point-of-view rather than strict language requirements or algorithmic correctness:


Classes should be named upper-case: Car, House, TwoTimesPlusOne, Addition
Interfaces should also be named upper-case: InfixOperator
Variable names should use camel-case: leafIndex, unsignedValue
i, j and k are used as iterator variables (the more you reference a variable, the shorter it should be named)
Prefer lists over arrays and make use of the enhanced for loop

for(InfixOperator i : operators) {
    //...
}



Adhering to common language standards will make your code more easily understandable for other programmers.