Complete the implementation of an expression tree that was begun in Segment XXXXXXXXXXAdd two constructors that create an expression tree given either a postfix expression or an infix expression....

Complete the implementation of an expression tree that was begun in Segment 25.17. Add two constructors that create an expression tree given either a postfix expression or an infix expression. Projects 4 and 5 in the previous chapter asked you to design algorithms for these two tasks. To simplify the method getValueOf, you can restrict the choice of variables and give them specific values.