import java.util.List;
import java.util.Stack;
/**
* Created by Lxx on 2017/4/29.
*/
public class InfixExpr {
String expr = null;
public InfixExpr(String expr){
this.expr = expr;
}
public float evaluate(){
TokenParser parser = new TokenParser();
List<Token> tokens = parser.parse(this.expr);
Stack<Token> opStack = new Stack<>();
Stack<Float> numStack = new Stack();
for(Token token : tokens){
if(token.isOperator()){
if(opStack.isEmpty()){
opStack.push(token);
}else {
while(!opStack.isEmpty() && !token.hasHigherPriority(opStack.peek())){
Token prevOperator = opStack.pop();
Float f2 = numStack.pop();
Float f1 = numStack.pop();
Float result = calculate(prevOperator.toString(),f1,f2);
numStack.push(result);
}
opStack.push(token);
}
}
if(token.isNumber()){
numStack.push(new Float(token.getIntValue()));
}
}
while (!opStack.isEmpty()){
Token token = opStack.pop();
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;
}
return null;
}
}