【新手求助】【JTree相关】学习点击事件的时候出现一些问题

[QiaoDog]

哈哈哈我又来向大家求助啦

最近在自学JTree相关的知识，碰到了一些问题



这是我在网上看到的一个范例，这个是点击某个节点，他会打印出来你选中的对象

下面的是这个程序的源码

import javax.swing.JFrame;
import javax.swing.JTree;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.DefaultMutableTreeNode;
 
public class TreeDemo {
    public static void main(String[] args) {
 
        // 创建没有父节点和子节点、但允许有子节点的树节点，并使用指定的用户对象对它进行初始化。
        // public DefaultMutableTreeNode(Object userObject)
        DefaultMutableTreeNode node1 = new DefaultMutableTreeNode("软件部");
        node1.add(new DefaultMutableTreeNode(new User("小花")));
        node1.add(new DefaultMutableTreeNode(new User("小虎")));
        node1.add(new DefaultMutableTreeNode(new User("小龙")));
 
        DefaultMutableTreeNode node2 = new DefaultMutableTreeNode("销售部");
        node2.add(new DefaultMutableTreeNode(new User("小叶")));
        node2.add(new DefaultMutableTreeNode(new User("小雯")));
        node2.add(new DefaultMutableTreeNode(new User("小夏")));
 
        DefaultMutableTreeNode top = new DefaultMutableTreeNode("职员管理");
 
        top.add(new DefaultMutableTreeNode(new User("总经理")));
        top.add(node1);
        top.add(node2);
        final JTree tree = new JTree(top);
        JFrame f = new JFrame("JTreeDemo");
        f.add(tree);
        f.setSize(300, 300);
        f.setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // 添加选择事件
        tree.addTreeSelectionListener(new TreeSelectionListener() {
 
            @Override
            public void valueChanged(TreeSelectionEvent e) {
                DefaultMutableTreeNode node = (DefaultMutableTreeNode) tree
                        .getLastSelectedPathComponent();
 
                if (node == null)
                    return;
 
                Object object = node.getUserObject();
                if (node.isLeaf()) {
                    User user = (User) object;
                    System.out.println("你选择了：" + user.toString());
                }
 
            }
        });
    }
}
 
class User {
    private String name;
 
    public User(String n) {
        name = n;
    }
 
    // 重点在toString，节点的显示文本就是toString
    public String toString() {
        return name;
    }
}

我想给这里面的user加上一个年龄的属性

[QiaoDog]

接1楼

我于是改了下这段代码 给 user 添加了一个 age的 属性，并且写了 toName（） 和 toAge () 两个方法

新的代码如下

import javax.swing.JFrame;
import javax.swing.JTree;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.DefaultMutableTreeNode;
 
public class TestTree {
    public static void main(String[] args) {
 
        DefaultMutableTreeNode node1 = new DefaultMutableTreeNode("软件部");
        node1.add(new DefaultMutableTreeNode(new User("小花",22)));
        node1.add(new DefaultMutableTreeNode(new User("小虎",29)));
        node1.add(new DefaultMutableTreeNode(new User("小龙",27)));
 
        DefaultMutableTreeNode node2 = new DefaultMutableTreeNode("销售部");
        node2.add(new DefaultMutableTreeNode(new User("小叶",23)));
        node2.add(new DefaultMutableTreeNode(new User("小雯",25)));
        node2.add(new DefaultMutableTreeNode(new User("小夏",26)));
 
        DefaultMutableTreeNode top = new DefaultMutableTreeNode("职员管理");
 
        top.add(new DefaultMutableTreeNode(new User("总经理",40)));
        top.add(node1);
        top.add(node2);
 
        final JTree tree = new JTree(top);
        JFrame f = new JFrame("JTreeDemo");
        f.add(tree);
        f.setSize(300, 300);
        f.setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // 添加选择事件
        tree.addTreeSelectionListener(new TreeSelectionListener() {
 
            @Override
            public void valueChanged(TreeSelectionEvent e) {
                DefaultMutableTreeNode node = (DefaultMutableTreeNode) tree
                        .getLastSelectedPathComponent();
 
                if (node == null)
                    return;
 
                Object object = node.getUserObject();
                if (node.isLeaf()) {
                    User user = (User) object;
                    System.out.println("你选择了：" + user.toName() + "，其年龄是" + user.toAge());
                }
 
            }
        });
    }
}
 
class User {
    private String name;
    private int age;
 
    public User(String n, int a) {
        name = n;
        age = a;
    }
 
    public String toName () {
    	return name;
    }
    
    public int toAge () {
    	return age;
    }
}

以下是我编译运行后的结果
发现有个问题：可以正常的打印出来user的属性，但是在GUI界面里面是不能显示user的名字的，这该怎么去改

[天上掉个大馅饼]

class User {
    private String name;
  
    public User(String n) {
        name = n;
    }
  
    // 重点在toString，节点的显示文本就是toString
    public String toString() {
        return name;
    }
}

案例里面已经说了 你的类里要重写toString

[QiaoDog]

引用 2 楼 lonrence 的回复:

class User {
    private String name;
  
    public User(String n) {
        name = n;
    }
  
    // 重点在toString，节点的显示文本就是toString
    public String toString() {
        return name;
    }
}

案例里面已经说了 你的类里要重写toString

那如果我要添加一个属性的话该怎么办

[QiaoDog]

我心生一计 就是在创建节点的时候我调用user的 toName 方法，这下应该能正常显示了吧，没想到在打印那块又出了问题
编译，运行都是正常的，但是在我点击了对象之后发现不能打印出来，会抛出错误

这是代码

import javax.swing.JFrame;
import javax.swing.JTree;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.DefaultMutableTreeNode;
 
public class TestTree {
    public static void main(String[] args) {
 
        DefaultMutableTreeNode node1 = new DefaultMutableTreeNode("软件部");
        node1.add(new DefaultMutableTreeNode(new User("小花",22).toName()));
        node1.add(new DefaultMutableTreeNode(new User("小虎",29).toName()));
        node1.add(new DefaultMutableTreeNode(new User("小龙",27).toName()));
 
        DefaultMutableTreeNode node2 = new DefaultMutableTreeNode("销售部");
        node2.add(new DefaultMutableTreeNode(new User("小叶",23).toName()));
        node2.add(new DefaultMutableTreeNode(new User("小雯",25).toName()));
        node2.add(new DefaultMutableTreeNode(new User("小夏",26).toName()));
 
        DefaultMutableTreeNode top = new DefaultMutableTreeNode("职员管理");
 
        top.add(new DefaultMutableTreeNode(new User("总经理",40).toName()));
        top.add(node1);
        top.add(node2);
 
        final JTree tree = new JTree(top);
        JFrame f = new JFrame("JTreeDemo");
        f.add(tree);
        f.setSize(300, 300);
        f.setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // 添加选择事件
        tree.addTreeSelectionListener(new TreeSelectionListener() {
 
            @Override
            public void valueChanged(TreeSelectionEvent e) {
                DefaultMutableTreeNode node = (DefaultMutableTreeNode) tree
                        .getLastSelectedPathComponent();
 
                if (node == null)
                    return;
 
                Object object = node.getUserObject();
                if (node.isLeaf()) {
                    User user = (User) object;
                    System.out.println("你选择了：" + user.toName() + "，其年龄是" + user.toAge());
                }
 
            }
        });
    }
}
 
class User {
    private String name;
    private int age;
 
    public User(String n, int a) {
        name = n;
        age = a;
    }
 
    public String toName () {
    	return name;
    }
    
    public int toAge () {
    	return age;
    }
}

这是运行结果

[天上掉个大馅饼]

就是说DefaultMutableTreeNode类中显示user的名字是调用的user类的 toString()方法，你的案例中显示“User@2dda6444”这样的信息也说明了现在调用的是继承自Object的 toString()方法，重写 toString()就行了 public String toName () { return name; } 改为 public String toString() { return name; }

[天上掉个大馅饼]

那如果我要添加一个属性的话该怎么办 [/quote] 如果你想在显示出来 就写在 toString()方法里 比如

	@Override
	public String toString() {
		return name + ", " + age;
	}

这样就会显示名字和年龄了