package com.coding.basic.stack.expr;
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(this.expr);
Stack<Float> numStack = new Stack<>();
for(Token token : tokens){
System.out.println(token+"----");
if(token.isNumber()){
numStack.push(new Float(token.getIntValue()));
} else{
Float f2 = numStack.pop();
Float f1 = numStack.pop();
numStack.push(calculate(token.toString(),f1,f2));
}
}
return numStack.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");
}
}