How to automatically resize a JTree in Java

To automatically resize a JTree, use the setVisibleRowCount() method in Java. At first, create a node in the tree −

DefaultMutableTreeNode node = new DefaultMutableTreeNode("Project");

Now, add nodes to the node created above −

DefaultMutableTreeNode node1 = new DefaultMutableTreeNode("App");
DefaultMutableTreeNode node2 = new DefaultMutableTreeNode("Website");
DefaultMutableTreeNode node3 = new DefaultMutableTreeNode("WebApp");
node.add(node1);
node.add(node2);
node.add(node3);

Now, create more nodes and set them as child nodes for the nodes we creted above −

DefaultMutableTreeNode one = new DefaultMutableTreeNode("Learning website");
DefaultMutableTreeNode two = new DefaultMutableTreeNode("Business website");
DefaultMutableTreeNode three = new DefaultMutableTreeNode("News publishing website");
DefaultMutableTreeNode four = new DefaultMutableTreeNode("Android app");
DefaultMutableTreeNode five = new DefaultMutableTreeNode("iOS app");
DefaultMutableTreeNode six = new DefaultMutableTreeNode("Editor WebApp");
node1.add(one);
node1.add(two);
node1.add(three);
node2.add(four);
node2.add(five);
node3.add(six);

Now, create a JTree and set the root node in it −

JTree tree = new JTree(node);

The following will display the scrollbane and only allow 8 rows to be visible −

tree.setVisibleRowCount(8);
JOptionPane.showMessageDialog(null, new JScrollPane(tree));

The following is an example to automatically resize a JTree −

Example

package my;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
public class SwingDemo {
   public static void main(String[] args) throws Exception {
      JFrame frame = new JFrame("Demo");
      DefaultMutableTreeNode node = new DefaultMutableTreeNode("Project");
      DefaultMutableTreeNode node1 = new DefaultMutableTreeNode("App");
      DefaultMutableTreeNode node2 = new DefaultMutableTreeNode("Website");
      DefaultMutableTreeNode node3 = new DefaultMutableTreeNode("WebApp");
      node.add(node1);
      node.add(node2);
      node.add(node3);
      DefaultMutableTreeNode one = new DefaultMutableTreeNode("Learning website");
      DefaultMutableTreeNode two = new DefaultMutableTreeNode("Business website");
      DefaultMutableTreeNode three = new DefaultMutableTreeNode("News publishing website");
      DefaultMutableTreeNode four = new DefaultMutableTreeNode("Android app");
      DefaultMutableTreeNode five = new DefaultMutableTreeNode("iOS app");
      DefaultMutableTreeNode six = new DefaultMutableTreeNode("Editor WebApp");
      node1.add(one);
      node1.add(two);
      node1.add(three);
      node2.add(four);
      node2.add(five);
      node3.add(six);
      JTree tree = new JTree(node);
      frame.add(tree);
      tree.setVisibleRowCount(8);
      JOptionPane.showMessageDialog(null, new JScrollPane(tree));
   }
}

Output

Now, when you will click on each node, then the sub-nodes will get displayed.. On extending the visible row count, a ScrollBar would be visible to resize the TREE −