package com.ralf.stack.expr;
import java.util.List;
import com.ralf.stack.MyStack;
public class PostfixExpr {
private String exprString;
public PostfixExpr(String exprString){
this.exprString = exprString;
}
public float evaluate() {
MyStack<Float> myStack = new MyStack<>();
TokenParser parser = new TokenParser();
List<Token> tokens = parser.parse(exprString);
for(Token token : tokens){
if (token.isNumber()) {
myStack.push(new Float(token.getValue()));
}
if (token.isOperator()) {
float f2 = myStack.pop();
float f1 = myStack.pop();
myStack.push(calculate(token.toString(), f1, f2));
}
}
return myStack.pop().floatValue();
}
private Float calculate(String op, Float f1, Float f2){
if(op.equals("+")){
return f1+f2;
}
if(op.equals("-")){
return f1-f2;
}
if(op.equals("*")){
return f1*f2;
}
if(op.equals("/")){
return f1/f2;
}
throw new RuntimeException(op + " is not supported");
}
}