Java Jtree mouseEvent如果未选择任何内容

Question

I am trying to figure out how to code a event that, if clicked in a Swing JTree and the mouse does not click anything in the tree, to get a println that says "nothing".

Say I have a tree 'info_tree' with an AWT.event.Mouwesvent as such:

private void info_treeMouseClicked(java.awt.event.MouseEvent evt) {   
    if(info_tree.getSelectionPath() /*something along the lines of is empty or if !info_tree.getSelectionPath().isEmpty()*/
       ){system.out.println("Nothing");
      }else{
          system.out.println("Something");
      }
}

I can't find anything to compare a selectedPath or element of a tree.

Answer 1

You may wish to try

If (info_tree.getSelectionPath()==null)

But,then you may want to switch your output lines around. Because that as-is is a true/false condition. If false it'll goto else. That could solve it as well.

Answer 2

You can try this program:

import javax.swing.*;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class JTreeGetSelectedNode extends JFrame {
    public JTreeGetSelectedNode() throws HeadlessException {
        initializeUI();
    }

    private void initializeUI() {
        setSize(200, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        DefaultMutableTreeNode root = new DefaultMutableTreeNode("Countries");
        DefaultMutableTreeNode asia = new DefaultMutableTreeNode("Asia");
        String[] countries = new String[] {"India", "Singapore", "Indonesia", "Vietnam"};
        for (String country : countries) {
            DefaultMutableTreeNode node = new DefaultMutableTreeNode(country);
            asia.add(node);
        }

        DefaultMutableTreeNode northAmerica = new DefaultMutableTreeNode("North America");
        countries = new String[] {"United States", "Canada"};
        for (String country : countries) {
            DefaultMutableTreeNode node = new DefaultMutableTreeNode(country);
            northAmerica.add(node);
        }

        DefaultMutableTreeNode southAmerica = new DefaultMutableTreeNode("South America");
        countries = new String[] {"Brazil", "Argetina", "Uruguay"};
        for (String country : countries) {
            DefaultMutableTreeNode node = new DefaultMutableTreeNode(country);
            southAmerica.add(node);
        }

        DefaultMutableTreeNode europe = new DefaultMutableTreeNode("Europe");
        countries = new String[] {"United Kingdom", "Germany", "Spain", "France", "Italy"};
        for (String country : countries) {
            DefaultMutableTreeNode node = new DefaultMutableTreeNode(country);
            europe.add(node);
        }

        root.add(asia);
        root.add(northAmerica);
        root.add(southAmerica);
        root.add(europe);

        final JTree tree = new JTree(root);
        JScrollPane pane = new JScrollPane(tree);
        pane.setPreferredSize(new Dimension(200, 400));


        JButton button = new JButton("Get Selected");
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                Object paths = tree.getLastSelectedPathComponent();

      if(paths == null){
      System.out.println("nothig");
      }else{
      System.out.println("Something");
      }
            }
        });

        getContentPane().setLayout(new BorderLayout());
        getContentPane().add(pane, BorderLayout.CENTER);
        getContentPane().add(button, BorderLayout.SOUTH);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new JTreeGetSelectedNode().setVisible(true);
            }
        });
    }
}