Implement initial UI with textbox

Co-Authored-By: td1223

src/main/java/ic/doc/RpnCalculator.java

@@ -0,0 +1,12 @@
+package ic.doc;
+
+public class RpnCalculator {
+  private static final int DEFAULT_WIDTH = 400;
+  private static final int DEFAULT_HEIGHT = 400;
+
+  public static void main(String[] args) {
+    RpnCalculatorGui calculatorGui = RpnCalculatorGui.withDimensions(DEFAULT_WIDTH, DEFAULT_HEIGHT);
+
+    calculatorGui.display();
+  }
+}

src/main/java/ic/doc/RpnCalculatorGui.java

@@ -0,0 +1,34 @@
+package ic.doc;
+
+import javax.swing.JFrame;
+import javax.swing.JPanel;
+import javax.swing.JTextField;
+
+public class RpnCalculatorGui {
+  private final int defaultWidth;
+  private final int defaultHeight;
+
+  private static final int RESULT_FIELD_WIDTH = 10;
+
+  public static RpnCalculatorGui withDimensions(int defaultWidth, int defaultHeight) {
+    return new RpnCalculatorGui(defaultWidth, defaultHeight);
+  }
+
+  private RpnCalculatorGui(int defaultWidth, int defaultHeight) {
+    this.defaultWidth = defaultWidth;
+    this.defaultHeight = defaultHeight;
+  }
+
+  public void display() {
+    JFrame frame = new JFrame("RPN Calculator");
+    frame.setSize(defaultWidth, defaultHeight);
+
+    JPanel panel = new JPanel();
+
+    JTextField resultField = new JTextField(RESULT_FIELD_WIDTH);
+    panel.add(resultField);
+
+    frame.add(panel);
+    frame.setVisible(true);
+  }
+}