2 files changed, 151 insertions, 0 deletions
diff --git a/src/de/fhswf/in/inf/java1/aufgabe11/UPN.java b/src/de/fhswf/in/inf/java1/aufgabe11/UPN.java
new file mode 100644
index 0000000..25b939e
--- /dev/null
+++ b/src/de/fhswf/in/inf/java1/aufgabe11/UPN.java
@@ -0,0 +1,110 @@
+/**
+ * 
+ */
+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+"))
+      {
+         try
+         {
+            upnStack.add(Double.valueOf(string));
+         }
+         catch (NumberFormatException e)
+         {
+            double operand1 = 0;
+            double operand2 = 0;
+            if (upnStack.size() < 2)
+            {
+               throw new IllegalStateException(
+                     "Two operands are needed for an operation.");
+            }
+
+            operand2 = upnStack.pop();
+            operand1 = upnStack.pop();
+
+            switch (string)
+            {
+               case "+":
+                  upnStack.add(operand1 + operand2);
+                  break;
+               case "-":
+                  upnStack.add(operand1 - operand2);
+                  break;
+               case "*":
+                  upnStack.add(operand1 * operand2);
+                  break;
+               case "/":
+                  if (operand2 == 0)
+                  {
+                     throw new IllegalArgumentException("Divisor can't be 0.");
+                  }
+                  upnStack.add(operand1 / operand2);
+                  break;
+               case "%":
+                  if (operand2 == 0)
+                  {
+                     throw new IllegalArgumentException("Divisor can't be 0.");
+                  }
+                  upnStack.add(operand1 % operand2);
+                  break;
+               default:
+                  throw new IllegalArgumentException("String: \"" + string
+                        + "\" is not a valid operator.");
+            }
+         }
+      }
+   }
+
+   /**
+    * 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 IllegalStateException("UPN stack is empty.");
+      }
+      return upnStack.peek();
+   }
+
+}
diff --git a/src/de/fhswf/in/inf/java1/aufgabe11/UpnMain.java b/src/de/fhswf/in/inf/java1/aufgabe11/UpnMain.java
new file mode 100644
index 0000000..a0f8a00
--- /dev/null
+++ b/src/de/fhswf/in/inf/java1/aufgabe11/UpnMain.java
@@ -0,0 +1,41 @@
+/**
+ * 
+ */
+package de.fhswf.in.inf.java1.aufgabe11;
+
+/**
+ * A class that povides a main.
+ *
+ * @author $Author: $
+ * @version $Revision: $, $Date: $ UTC
+ */
+public final class UpnMain
+{
+
+   /**
+    * Private constructor for utility class.
+    *
+    */
+   private UpnMain()
+   {
+      // TODO Auto-generated constructor stub
+   }
+
+   /**
+    * Main entry point for the exercise 11.
+    *
+    * @param args
+    *           Command line arguments.
+    */
+   public static void main(String[] args)
+   {
+
+      UPN test = new UPN();
+      
+      test.calculate("5 3 - 2 * 10 9 - / 10 6 - 8 6 - 2 * / -");
+
+      System.out.println(test.getResult());
+
+   }
+
+}