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/**
*
*/
package de.fhswf.in.inf.java1.aufgabe11;
import java.util.Stack;
/**
* A class that calculates in UPN.
*
* @author $Author: $
* @version $Revision: $, $Date: $ UTC
*/
public class UPN
{
private Stack<Double> upnStack = new Stack<>();
/**
* Empty constructor.
*
*/
public UPN()
{
}
/**
* Reads a string and puts it on the UPN upnStack.
*
* @param upnString
* A space delimited string in UPN notation.
*/
public final void calculate(String upnString)
{
if (upnString == null)
{
throw new IllegalArgumentException("UpnString can't be null.");
}
if (upnString.isEmpty())
{
throw new IllegalArgumentException("UpnString can't be empty.");
}
for (String string : upnString.split("\\s+"))
{
if (!string.isEmpty())
{
Double[] operands = null;
switch (string)
{
case "+":
operands = fetch();
upnStack.add(operands[0] + operands[1]);
break;
case "-":
operands = fetch();
upnStack.add(operands[0] - operands[1]);
break;
case "*":
operands = fetch();
upnStack.add(operands[0] * operands[1]);
break;
case "/":
divisorZero();
operands = fetch();
upnStack.add(operands[0] / operands[1]);
break;
case "%":
divisorZero();
operands = fetch();
upnStack.add(operands[0] % operands[1]);
break;
default:
try
{
upnStack.add(Double.valueOf(string));
}
catch (NumberFormatException e)
{
throw new IllegalArgumentException("String: \"" + string
+ "\" is not a valid"
+ " operator nor a valid operand.");
}
}
}
}
}
/**
* Get the result of a calculation done before.
*
* @return The top most value on the UPN stack.
*/
public final double getResult()
{
if (upnStack.empty())
{
throw new IllegalArgumentException("UPN stack is empty.");
}
return upnStack.peek();
}
/**
* Checks if Divisor will be zero.
*
*/
private void divisorZero()
{
if (upnStack.peek() == 0.0)
{
throw new IllegalArgumentException("Divisor can't be 0.");
}
}
/**
* Checks if there are two values on the stack and returns them.
*
* @return The two top most doubles from the stack.
*/
private Double[] fetch()
{
if (upnStack.size() < 2)
{
throw new IllegalArgumentException(
"Two operands are needed for an operation.");
}
Double[] ret = new Double[2];
ret[1] = upnStack.pop();
ret[0] = upnStack.pop();
return ret;
}
}
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