JAVA programing

Implement a system which allows the definition of variables and their associated truth values. The system should allow new variables to be added to the definition and the retrieval of the value of a given variable. For example, add(Z, false) would add a new variable to the system with a truth value of false. The function get(Z) would retrieve the current truth value of the variable Z in the system. Additionally, implement a simple evaluator which will find the truth value of simple expressions. The expressions should allow variables. The expressions can include the boolean operations: and, or, not, xor, implication, and biconditional.