Java Swing How to - Create JTree from ArrayList

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Question

We would like to know how to create JTree from ArrayList.

Answer

import java.awt.BorderLayout;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.List;
// ww w .j a  v  a2 s.c  o m
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.event.TreeModelListener;
import javax.swing.tree.TreeModel;
import javax.swing.tree.TreeNode;
import javax.swing.tree.TreePath;

public class Main {
  public static void main(String[] args) {
    JTree tree = new JTree(new TestModel());
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLayout(new BorderLayout());
    frame.add(new JScrollPane(tree));
    frame.pack();
    frame.setVisible(true);
  }
}
class TestModel implements TreeModel {

  Element data;

  TestModel() {
    data = new Element("data");
    data.add(new Element("One"));
    data.add(new Element("Two"));
    data.add(new Element("Three"));
    data.add(new Element("Four"));
    data.add(new Element("Five"));
  }
  @Override
  public Object getRoot() {
    return data;
  }

  @Override
  public Object getChild(Object parent, int index) {

    System.out.println("GetChild from " + parent + " @ " + index);

    if (parent instanceof Element) {
      Element p = (Element) parent;
      Object child = p.getChildAt(index);

      System.out.println("child = " + child);
      return child;
    }
    return null;
  }

  @Override
  public int getChildCount(Object parent) {
    if (parent instanceof Element) {
      Element e = (Element) parent;
      System.out.println("childCount = " + parent + "; " + e.getChildCount());
      return e.getChildCount();
    }
    return 0;
  }
  @Override
  public int getIndexOfChild(Object parent, Object child) {
    if (parent instanceof Element && child instanceof Element) {
      Element e = (Element) parent;
      System.out.println("indexOf " + child + " in " + parent + " is "
          + e.getIndex((Element) child));
      return e.getIndex((Element) child);
    }
    return -1;
  }
  @Override
  public boolean isLeaf(Object node) {
    if (node instanceof Element) {
      Element e = (Element) node;
      System.out.println("isLeaf " + e + "; " + (e.getChildCount() == 0));
      return e.getChildCount() == 0;
    }
    return true;
  }
  @Override
  public void valueForPathChanged(TreePath path, Object newValue) {
  }
  @Override
  public void addTreeModelListener(TreeModelListener l) {
  }
  @Override
  public void removeTreeModelListener(TreeModelListener l) {
  }
}
class Element implements TreeNode {
  List<Element> nodes;
  Element parent;
  String name;
  public Element(String n) {
    nodes = new ArrayList<>(25);
    name = n;
  }

  @Override
  public String toString() {
    return name;
  }
  protected void setParent(Element parent) {
    this.parent = parent;
  }
  public void add(Element node) {
    node.setParent(this);
    nodes.add(node);
  }
  public void remove(Element node) {
    node.setParent(null);
    nodes.remove(node);
  }

  @Override
  public TreeNode getChildAt(int childIndex) {
    return nodes.get(childIndex);
  }

  @Override
  public int getChildCount() {
    return nodes.size();
  }

  @Override
  public TreeNode getParent() {
    return parent;
  }

  @Override
  public int getIndex(TreeNode node) {
    return nodes.indexOf(node);
  }

  @Override
  public boolean getAllowsChildren() {
    return true;
  }

  @Override
  public boolean isLeaf() {
    return nodes.isEmpty();
  }

  @Override
  public Enumeration children() {
    return Collections.enumeration(nodes);
  }
}

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