diff -r 3b8b1da2ff29 -r 12b1f4649ab1 src/Tools/GraphBrowser/awt/MessageDialog.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Tools/GraphBrowser/awt/MessageDialog.java	Fri Jul 16 12:55:02 2021 +0200
@@ -0,0 +1,53 @@
+/***************************************************************************
+  Title:      awt/MessageDialog.java
+  Author:     Stefan Berghofer, TU Muenchen
+
+  This class defines a dialog window for displaying messages and buttons.
+***************************************************************************/
+
+package isabelle.awt;
+
+import java.awt.*;
+import java.awt.event.*;
+
+public class MessageDialog extends Dialog implements ActionListener {
+	String txt;
+
+	public String getText() { return txt; }
+
+	public void actionPerformed(ActionEvent evt) {
+		txt = evt.getActionCommand();
+		setVisible(false);
+	}
+
+	public MessageDialog(Frame parent,String title,String text,String []buttons) {
+		super(parent,title,true);
+		int i;
+		Panel p1=new Panel(),p2=new Panel();
+		p1.setLayout(new FlowLayout(FlowLayout.CENTER,0,0));
+		p2.setLayout(new FlowLayout());
+		setFont(new Font("Helvetica", Font.PLAIN, 14));
+		setLayout(new GridLayout(2,1));
+
+		while (true) {
+			int pos=text.indexOf(' ');
+			if (pos<0) {
+				p1.add(new Label(text));
+				break;
+			} else {
+				p1.add(new Label(text.substring(0,pos)));
+				if (pos+1==text.length())
+					break;
+				else
+					text=text.substring(pos+1);
+			}
+		}
+
+		add(p1);add(p2);
+		for (i=0;i<buttons.length;i++) {
+			Button bt = new Button(buttons[i]);
+			p2.add(bt);
+			bt.addActionListener(this);
+		}
+	}
+}