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I was looking for a a JTree implementation, that contains checkboxes and which:

  • When you select one node, all its successors in the tree are automatically selected

  • When you unselect one node, all its successors in the tree are automatically unselected

  • When a parent node is already selected, and the selection was removed from one of its successors, the node color will be changed, to make it intuitive that although this parent node is selected, not all of its successors are selected (Like when you select components to install in common installers)

  • A click on a node leads to (No need to hold 'Ctrl' key!):

    • If the node is already selected, it becomes unselected, with all its successors
    • If the node is not selected, it becomes selected, with all its successors

I searched the net for something simple, but could not find something as simple as I wanted.

Does anyone know a good implementation of such tree?

Question author Somethingsomething | Source

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Answering myself:

I decided to share my code with everyone.

Here's a screenshot of the result:

Screenshot

The implementation details:

  • Created a new class that extends JTree

  • Replaced the 'TreeCellRenderer' by a new class I created, that shows a checkbox and a label. The checkbox selection is changed instead of the label background and border.

  • Totally terminated the selection mechanism. Replaced the 'Selection Model' by a 'DefaultTreeSelectionModel' overridden inline, that has empty implementation

    • Created new event type for checking of the checkboxes

    • Created special data structures that help to indicate fast the state of each node

Enjoy!!

Here's a usage example:

public class Main extends JFrame {

    private static final long serialVersionUID = 4648172894076113183L;

    public Main() {
        super();
        setSize(500, 500);
        this.getContentPane().setLayout(new BorderLayout());
        final JCheckBoxTree cbt = new JCheckBoxTree();
        this.getContentPane().add(cbt);
        cbt.addCheckChangeEventListener(new JCheckBoxTree.CheckChangeEventListener() {
            public void checkStateChanged(JCheckBoxTree.CheckChangeEvent event) {
                System.out.println("event");
                TreePath[] paths = cbt.getCheckedPaths();
                for (TreePath tp : paths) {
                    for (Object pathPart : tp.getPath()) {
                        System.out.print(pathPart + ",");
                    }                   
                    System.out.println();
                }
            }           
        });         
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    public static void main(String args[]) {
        Main m = new Main();
        m.setVisible(true);
    }
}

Here is the source code of the class itself:

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.util.EventListener;
import java.util.EventObject;
import java.util.HashMap;
import java.util.HashSet;

import javax.swing.JCheckBox;
import javax.swing.JPanel;
import javax.swing.JTree;
import javax.swing.event.EventListenerList;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeSelectionModel;
import javax.swing.tree.TreeCellRenderer;
import javax.swing.tree.TreeModel;
import javax.swing.tree.TreeNode;
import javax.swing.tree.TreePath;

public class JCheckBoxTree extends JTree {

    private static final long serialVersionUID = -4194122328392241790L;

    JCheckBoxTree selfPointer = this;



    // Defining data structure that will enable to fast check-indicate the state of each node
    // It totally replaces the "selection" mechanism of the JTree
    private class CheckedNode {
        boolean isSelected;
        boolean hasChildren;
        boolean allChildrenSelected;

        public CheckedNode(boolean isSelected_, boolean hasChildren_, boolean allChildrenSelected_) {
            isSelected = isSelected_;
            hasChildren = hasChildren_;
            allChildrenSelected = allChildrenSelected_;
        }
    }
    HashMap<TreePath, CheckedNode> nodesCheckingState;
    HashSet<TreePath> checkedPaths = new HashSet<TreePath>();

    // Defining a new event type for the checking mechanism and preparing event-handling mechanism
    protected EventListenerList listenerList = new EventListenerList();

    public class CheckChangeEvent extends EventObject {     
        private static final long serialVersionUID = -8100230309044193368L;

        public CheckChangeEvent(Object source) {
            super(source);          
        }       
    }   

    public interface CheckChangeEventListener extends EventListener {
        public void checkStateChanged(CheckChangeEvent event);
    }

    public void addCheckChangeEventListener(CheckChangeEventListener listener) {
        listenerList.add(CheckChangeEventListener.class, listener);
    }
    public void removeCheckChangeEventListener(CheckChangeEventListener listener) {
        listenerList.remove(CheckChangeEventListener.class, listener);
    }

    void fireCheckChangeEvent(CheckChangeEvent evt) {
        Object[] listeners = listenerList.getListenerList();
        for (int i = 0; i < listeners.length; i++) {
            if (listeners[i] == CheckChangeEventListener.class) {
                ((CheckChangeEventListener) listeners[i + 1]).checkStateChanged(evt);
            }
        }
    }

    // Override
    public void setModel(TreeModel newModel) {
        super.setModel(newModel);
        resetCheckingState();
    }

    // New method that returns only the checked paths (totally ignores original "selection" mechanism)
    public TreePath[] getCheckedPaths() {
        return checkedPaths.toArray(new TreePath[checkedPaths.size()]);
    }

    // Returns true in case that the node is selected, has children but not all of them are selected
    public boolean isSelectedPartially(TreePath path) {
        CheckedNode cn = nodesCheckingState.get(path);
        return cn.isSelected && cn.hasChildren && !cn.allChildrenSelected;
    }

    private void resetCheckingState() { 
        nodesCheckingState = new HashMap<TreePath, CheckedNode>();
        checkedPaths = new HashSet<TreePath>();
        DefaultMutableTreeNode node = (DefaultMutableTreeNode)getModel().getRoot();
        if (node == null) {
            return;
        }
        addSubtreeToCheckingStateTracking(node);
    }

    // Creating data structure of the current model for the checking mechanism
    private void addSubtreeToCheckingStateTracking(DefaultMutableTreeNode node) {
        TreeNode[] path = node.getPath();   
        TreePath tp = new TreePath(path);
        CheckedNode cn = new CheckedNode(false, node.getChildCount() > 0, false);
        nodesCheckingState.put(tp, cn);
        for (int i = 0 ; i < node.getChildCount() ; i++) {              
            addSubtreeToCheckingStateTracking((DefaultMutableTreeNode) tp.pathByAddingChild(node.getChildAt(i)).getLastPathComponent());
        }
    }

    // Overriding cell renderer by a class that ignores the original "selection" mechanism
    // It decides how to show the nodes due to the checking-mechanism
    private class CheckBoxCellRenderer extends JPanel implements TreeCellRenderer {     
        private static final long serialVersionUID = -7341833835878991719L;     
        JCheckBox checkBox;     
        public CheckBoxCellRenderer() {
            super();
            this.setLayout(new BorderLayout());
            checkBox = new JCheckBox();
            add(checkBox, BorderLayout.CENTER);
            setOpaque(false);
        }

        @Override
        public Component getTreeCellRendererComponent(JTree tree, Object value,
                boolean selected, boolean expanded, boolean leaf, int row,
                boolean hasFocus) {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode)value;
            Object obj = node.getUserObject();          
            TreePath tp = new TreePath(node.getPath());
            CheckedNode cn = nodesCheckingState.get(tp);
            if (cn == null) {
                return this;
            }
            checkBox.setSelected(cn.isSelected);
            checkBox.setText(obj.toString());
            checkBox.setOpaque(cn.isSelected && cn.hasChildren && ! cn.allChildrenSelected);
            return this;
        }       
    }

    public JCheckBoxTree() {
        super();
        // Disabling toggling by double-click
        this.setToggleClickCount(0);
        // Overriding cell renderer by new one defined above
        CheckBoxCellRenderer cellRenderer = new CheckBoxCellRenderer();
        this.setCellRenderer(cellRenderer);

        // Overriding selection model by an empty one
        DefaultTreeSelectionModel dtsm = new DefaultTreeSelectionModel() {      
            private static final long serialVersionUID = -8190634240451667286L;
            // Totally disabling the selection mechanism
            public void setSelectionPath(TreePath path) {
            }           
            public void addSelectionPath(TreePath path) {                       
            }           
            public void removeSelectionPath(TreePath path) {
            }
            public void setSelectionPaths(TreePath[] pPaths) {
            }
        };
        // Calling checking mechanism on mouse click
        this.addMouseListener(new MouseListener() {
            public void mouseClicked(MouseEvent arg0) {
                TreePath tp = selfPointer.getPathForLocation(arg0.getX(), arg0.getY());
                if (tp == null) {
                    return;
                }
                boolean checkMode = ! nodesCheckingState.get(tp).isSelected;
                checkSubTree(tp, checkMode);
                updatePredecessorsWithCheckMode(tp, checkMode);
                // Firing the check change event
                fireCheckChangeEvent(new CheckChangeEvent(new Object()));
                // Repainting tree after the data structures were updated
                selfPointer.repaint();                          
            }           
            public void mouseEntered(MouseEvent arg0) {         
            }           
            public void mouseExited(MouseEvent arg0) {              
            }
            public void mousePressed(MouseEvent arg0) {             
            }
            public void mouseReleased(MouseEvent arg0) {
            }           
        });
        this.setSelectionModel(dtsm);
    }

    // When a node is checked/unchecked, updating the states of the predecessors
    protected void updatePredecessorsWithCheckMode(TreePath tp, boolean check) {
        TreePath parentPath = tp.getParentPath();
        // If it is the root, stop the recursive calls and return
        if (parentPath == null) {
            return;
        }       
        CheckedNode parentCheckedNode = nodesCheckingState.get(parentPath);
        DefaultMutableTreeNode parentNode = (DefaultMutableTreeNode) parentPath.getLastPathComponent();     
        parentCheckedNode.allChildrenSelected = true;
        parentCheckedNode.isSelected = false;
        for (int i = 0 ; i < parentNode.getChildCount() ; i++) {                
            TreePath childPath = parentPath.pathByAddingChild(parentNode.getChildAt(i));
            CheckedNode childCheckedNode = nodesCheckingState.get(childPath);           
            // It is enough that even one subtree is not fully selected
            // to determine that the parent is not fully selected
            if (! childCheckedNode.allChildrenSelected) {
                parentCheckedNode.allChildrenSelected = false;      
            }
            // If at least one child is selected, selecting also the parent
            if (childCheckedNode.isSelected) {
                parentCheckedNode.isSelected = true;
            }
        }
        if (parentCheckedNode.isSelected) {
            checkedPaths.add(parentPath);
        } else {
            checkedPaths.remove(parentPath);
        }
        // Go to upper predecessor
        updatePredecessorsWithCheckMode(parentPath, check);
    }

    // Recursively checks/unchecks a subtree
    protected void checkSubTree(TreePath tp, boolean check) {
        CheckedNode cn = nodesCheckingState.get(tp);
        cn.isSelected = check;
        DefaultMutableTreeNode node = (DefaultMutableTreeNode) tp.getLastPathComponent();
        for (int i = 0 ; i < node.getChildCount() ; i++) {              
            checkSubTree(tp.pathByAddingChild(node.getChildAt(i)), check);
        }
        cn.allChildrenSelected = check;
        if (check) {
            checkedPaths.add(tp);
        } else {
            checkedPaths.remove(tp);
        }
    }

}
Answer author Somethingsomething