JTree: Set custom open/closed icons for individual groups

Question

1. I know how to set custom leaf icons in JTree
2. I know how to set custom closed/open icons for all group nodes

But I can not set custom open/closed icons based on the group node names, for example of node could be called Emails (so it is nice to have an envelop icon) or one group may be called tasks and so on.

I tried to do this by overriding the getTreeCellRendererComponent method of class DefaultTreeCellRenderer

But changing the icon for the current node will affect for the next node only!

How to set custom open/closed icons for individual groups?

Please take a look at my code:

Employee.java

package com.ehsunbehravesh.swing;

import java.util.Random;

public class Employee {

  public String name;
  public int id;
  public boolean isBoss;
  public Employee[] employees;

  public Employee(String name, boolean isBoss) {
    this.name = name;
    this.isBoss = isBoss;
    this.id = new Random(System.currentTimeMillis()).nextInt(Integer.MAX_VALUE);
  }  

  @Override
  public String toString() {
    return this.name;
  }

    static String randomName() {
    String chars = "abcdefghijklmnopqrstuvwxyz";
    StringBuilder builder = new StringBuilder();
    Random r = new Random(System.currentTimeMillis());
    int length = r.nextInt(10) + 1;
    for (int i = 0; i < length; i++) {
      builder.append(chars.charAt(r.nextInt(chars.length())));
    }

    return builder.toString();
  }
}

CustomTreeNode.java

package com.ehsunbehravesh.swing;

import javax.swing.ImageIcon;
import javax.swing.tree.DefaultMutableTreeNode;

public class CustomTreeNode extends DefaultMutableTreeNode {

  /**
   * The icon which is displayed on the JTree object. open, close, leaf icon.
   */
  private ImageIcon icon;

  public CustomTreeNode(ImageIcon icon) {
    this.icon = icon;
  }

  public CustomTreeNode(ImageIcon icon, Object userObject) {
    super(userObject);
    this.icon = icon;
  }

  public CustomTreeNode(ImageIcon icon, Object userObject, boolean allowsChildren) {
    super(userObject, allowsChildren);
    this.icon = icon;
  }

  public ImageIcon getIcon() {
    return icon;
  }

  public void setIcon(ImageIcon icon) {
    this.icon = icon;
  }    
}

CustomeTreeCellRenderer.java

package com.ehsunbehravesh.swing;

import java.awt.Component;
import javax.swing.JTree;
import javax.swing.tree.DefaultTreeCellRenderer;

class CustomeTreeCellRenderer extends DefaultTreeCellRenderer {

  public CustomeTreeCellRenderer() {
  }

  @Override
  public Component getTreeCellRendererComponent(JTree tree, Object value, boolean selected, boolean expanded, boolean leaf, int row, boolean hasFocus) {
    super.getTreeCellRendererComponent(tree, value, leaf, expanded, leaf, row, hasFocus);

    if (!leaf) {
      CustomTreeNode node = (CustomTreeNode) value;
      System.out.println(((Employee) node.getUserObject()).name);

      if (node.getIcon() != null) {
        System.out.println(node.getIcon().toString());
        setClosedIcon(node.getIcon());
        setOpenIcon(node.getIcon());
      } else {
        setClosedIcon(getDefaultClosedIcon());
        setClosedIcon(getDefaultOpenIcon());
        setOpenIcon(getDefaultOpenIcon());
      }
    }

    return this;
  }
}

Test1.java

package com.ehsunbehravesh.swing;

import java.awt.BorderLayout;
import java.awt.Color;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTree;
import javax.swing.tree.DefaultTreeModel;

class TreeSample {
  public static void main(String args[]) {
    JFrame f = new JFrame("JTree Sample");
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JPanel pnlMain = new JPanel(new BorderLayout());
    pnlMain.setBackground(Color.white);

    createTree(pnlMain);

    f.setContentPane(pnlMain);

    f.setSize(300, 200);
    f.setVisible(true);
  }

  private static void createTree(JPanel pnlMain) {
    Employee bigBoss = new Employee(Employee.randomName(), true);
    Employee[] level1 = new Employee[5];    
    bigBoss.employees = level1;

    for (int i = 0; i < level1.length; i++) {
      level1[i] = new Employee(Employee.randomName(), true);      
    }


    for (int i = 0; i < level1.length; i++) {
      Employee employee = level1[i];
      if (employee.isBoss) {
        int count = 5;
        employee.employees = new Employee[count];

        for (int j = 0; j < employee.employees.length; j++) {
          employee.employees[j] = new Employee(Employee.randomName(), false);          
        }
      }
    }

    CustomTreeNode root = new CustomTreeNode(new ImageIcon("images/Circle_3.gif"), bigBoss);           
    DefaultTreeModel model = new DefaultTreeModel(root);

    for (Employee employee : bigBoss.employees) {
      CustomTreeNode boss = new CustomTreeNode(new ImageIcon("images/Circle_2.gif"), employee);
      root.add(boss);
      if (employee.isBoss) {                
        for (Employee employee1 : employee.employees) {
          CustomTreeNode emp = new CustomTreeNode(new ImageIcon("images/Circle_1.gif"), employee1);
          boss.add(emp);
        }
      }
    }

    JTree tree = new JTree(model);
    tree.setCellRenderer(new CustomeTreeCellRenderer());            
    pnlMain.add(tree, BorderLayout.CENTER);
  }  
}

Answer 1

In your TreeCellRenderer, you can use setOpenIcon() and setClosedIcon() as required in conjunction with the defined parameters and predicates related to your model. Given a tree having the default JTree model, the TreeRenderer below will use the closed and open icons for the sports node:

private static class TreeRenderer extends DefaultTreeCellRenderer {

    private static final Icon closed =
        (Icon) UIManager.get("InternalFrame.maximizeIcon");
    private static final Icon open =
        (Icon) UIManager.get("InternalFrame.minimizeIcon");

    @Override
    public Component getTreeCellRendererComponent(JTree tree, Object value,
        boolean sel, boolean exp, boolean leaf, int row, boolean hasFocus) {
        DefaultMutableTreeNode node = (DefaultMutableTreeNode) value;
        String s = node.getUserObject().toString();
        if ("sports".equals(s)) {
            setOpenIcon(open);
            setClosedIcon(closed);
        } else {
            setOpenIcon(getDefaultOpenIcon());
            setClosedIcon(getDefaultClosedIcon());
        }
        super.getTreeCellRendererComponent(
            tree, value, sel, exp, leaf, row, hasFocus);
        return this;
    }
}

See also this related example.

Answer 2

Having run you code, it would appear that the images you are trying to load are "meant" to be embedded within you application (that is, they don't reside some where on the disk out side of the application context).

So instead of doing this...

CustomTreeNode root = new CustomTreeNode(new ImageIcon("images/Circle_3.gif"), bigBoss); 

Try doing something like this...

CustomTreeNode root = new CustomTreeNode(new ImageIcon(ImageIO.read(getClass().getResource("/images/Circle_3.gif"))), bigBoss); 

Instead. This will cause Java to look within it's class path (including any JAR resources) to find the images.

When I run you code without this fix, nothing worked, when I updated it to use this feature, it worked fine.

NB: ImageIO#read throws an IOException so look out for it

Updated

After much head scratching...I changed the cell renderer to look like this...

class CustomeTreeCellRenderer extends DefaultTreeCellRenderer {

    public CustomeTreeCellRenderer() {
    }

    @Override
    public Component getTreeCellRendererComponent(JTree tree, Object value, boolean selected, boolean expanded, boolean leaf, int row, boolean hasFocus) {

//            if (!leaf) {
        CustomTreeNode node = (CustomTreeNode) value;

        if (node.getIcon() != null) {
            System.out.println(node + " - " + node.getIcon());
            setClosedIcon(node.getIcon());
            setOpenIcon(node.getIcon());
            setLeafIcon(node.getIcon());
        } else {
            System.out.println(node + " - default");
            setClosedIcon(getDefaultClosedIcon());
            setLeafIcon(getDefaultLeafIcon());
            setOpenIcon(getDefaultOpenIcon());
        }
//            }

        super.getTreeCellRendererComponent(tree, value, selected, expanded, leaf, row, hasFocus);

        return this;
    }
}

It it cleared it all up...

Calling setXxxIcon doesn't effect the current renderer, but the future renderer. That is. If you call setOpenIcon AFTER you've already called super.getTreeCellRendererComponent, it will not effect the current renderer, but it will effect the next call to super.getTreeCellRendererComponent as the set method is simply setting the value of class variable.

Additional

Trashgod has made a valuable comment about relying on the implementation and the way it works now.

Instead of calling DefaultTreeCellRenderer#setXxxIcon within the getTreeCellRendererComponent method, you should actually simply call DefaultTreeCellRenderer#setIcon, using the required icon based on the parameters passed to it.

This means you can call super.getTreeCellRendererComponent first and then override the behavior of the icons after it.

You could also grab a reference to Object value and override the DefaultTreeCellRenderer#getXxxIcon methods and based on the value, change the return values of these methods. I personally, wouldn't courage this as it changes the documented behavior of the renderer