package com.coding.basic.stack.myself;
import java.util.List;
import java.util.Stack;
public class PostfixExpr {
String expr = null;
public PostfixExpr(String expr) {
this.expr = expr;
}
public float evaluate() {
TokenParser parser = new TokenParser();
List<Token> tokens = parser.parse(expr);
Stack<Float> numStack = new Stack<Float>();
for (Token token:tokens){
if (token.isNumber()){
numStack.push(new Float(token.getIntValue()));
}else{
float f2 = numStack.pop();
float f1 = numStack.pop();
float result = calculate(token.toString(), f1, f2);
numStack.push(result);
}
}
return numStack.pop().floatValue();
}
public 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");
}
}