Some little replacement work

src/de/itstall/TaschenrechnerGui.java

@@ -68,11 +68,29 @@ public class TaschenrechnerGui extends JFrame {
 		panel.add(button);
 	}
 
+	public String replaceSigns(String strDisplay) {
+
+		if(strDisplay.startsWith("= ") && !(strDisplay.endsWith("+") || strDisplay.endsWith("-") || strDisplay.endsWith("*") || strDisplay.endsWith("/"))) {
+			strDisplay = strDisplay.substring(strDisplay.length()-1);
+		} else {
+			strDisplay = strDisplay.replace("= ", "");
+			strDisplay = strDisplay.replace("**", "*");
+			strDisplay = strDisplay.replace("//", "/");
+			strDisplay = strDisplay.replace("/*", "*");
+			strDisplay = strDisplay.replace("++", "+");
+			strDisplay = strDisplay.replace("--", "-");
+			strDisplay = strDisplay.replace("-+-", "-");
+			strDisplay = strDisplay.replace("+-+", "+");
+		}
+
+		return strDisplay;
+	}
+
 	private class InsertAction implements ActionListener {
 
 		@Override
 		public void actionPerformed(ActionEvent actionEvent) {
-			txtCalculation.setText(txtCalculation.getText() + ((JButton) actionEvent.getSource()).getText());
+			txtCalculation.setText(replaceSigns(txtCalculation.getText() + ((JButton) actionEvent.getSource()).getText()));
 		}
 	}
 
@@ -80,7 +98,7 @@ public class TaschenrechnerGui extends JFrame {
 
 		@Override
 		public void actionPerformed(ActionEvent actionEvent) {
-			txtCalculation.setText(" = " + String.valueOf(berechnen(txtCalculation.getText())));
+			txtCalculation.setText("= " + String.valueOf(berechnen(txtCalculation.getText())));
 		}
 	}