Question

I’m trying to select the first row on a JTree when i create it.
But sometimes i get the following exception:

java.lang.NullPointerException
   at javax.swing.plaf.basic.BasicTreeUI.completeEditing(BasicTreeUI.java:2035)
   at javax.swing.plaf.basic.BasicTreeUI$Handler.valueChanged(BasicTreeUI.java:3715)
   at javax.swing.tree.DefaultTreeSelectionModel.fireValueChanged(DefaultTreeSelectionModel.java:634)
   at javax.swing.tree.DefaultTreeSelectionModel.notifyPathChange(DefaultTreeSelectionModel.java:1092)
   at javax.swing.tree.DefaultTreeSelectionModel.setSelectionPaths(DefaultTreeSelectionModel.java:293)
   at javax.swing.JTree.setSelectionPaths(JTree.java:1644)
   at javax.swing.JTree.setSelectionRows(JTree.java:1721)
   at javax.swing.JTree.setSelectionRow(JTree.java:1696)

before calling the tree.setSelectionRow(0) i try to put the following check without any effect:

    while((!tabTree.isVisible()) || (tabTree.isEditing()) || (tabTree.getRowCount() == 0)) {
        try {
            Thread.sleep(10);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    tabTree.setSelectionRow(0);

You need to be saved 🙂

any suggestions?

Answer 1

This can be caused by:

• You’re using a custom cell editor which returns null in getTreeCellEditorComponent()
• You modify the tree in a non-UI thread. See Concurrency in Swing.