JTree，setUserObject（），toString（）

Question

我想做的很簡單，但是遇到了一些問題。 我有一個類，我用一些值覆蓋toString（）。

public class AClass {

@Override
public String toString() {
    int rand = 5 + (int) (Math.random() * 25);
    return Integer.toString(rand);
    }
}

我有一個JTree，並通過使用setUserObject（）將類對象添加到節點。 節點上的顯示現在具有toString（）中的值。

            DefaultMutableTreeNode  node = new DefaultMutableTreeNode();
            node.setUserObject(new AClass());
            fileTreeModel.insertNodeInto(node, (DefaultMutableTreeNode) rootNode, 0);
            tree.setSelectionPath(new TreePath(fileTreeModel.getPathToRoot(node)));
            tree.expandPath(new TreePath(rootNode.getPath()));

但是，當我單擊節點或嘗試添加新節點時，toString（）值正在更改。

這是怎么回事？ 任何幫助是極大的贊賞。 這是一些示例代碼。

Main.java

import java.awt.Color;
import java.awt.EventQueue;

import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JSplitPane;

import java.awt.BorderLayout;

import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.TreePath;
import javax.swing.tree.TreeSelectionModel;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

import javax.swing.JScrollPane;


public class Main {

private JFrame frame;
private JTree tree;
private DefaultMutableTreeNode rootNode ;
private DefaultTreeModel fileTreeModel;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                Main window = new Main();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the application.
 */
public Main() {
    initialize();
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 450, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JSplitPane splitPane = new JSplitPane();
    splitPane.setResizeWeight(0.2);
    frame.getContentPane().add(splitPane, BorderLayout.CENTER);

    JScrollPane scrollPane = new JScrollPane();
    splitPane.setLeftComponent(scrollPane);

    tree = new JTree();
    tree.setBackground(new Color(255, 235, 205));
    scrollPane.setViewportView(tree);
    rootNode = new DefaultMutableTreeNode("Files");
    fileTreeModel = new DefaultTreeModel(rootNode);
    tree.setModel(fileTreeModel);
    tree.getSelectionModel().setSelectionMode(
            TreeSelectionModel.SINGLE_TREE_SELECTION);
    tree.setRootVisible(true);

    JDesktopPane desktopPane = new JDesktopPane();
    desktopPane.setBackground(new Color(255, 255, 0));
    splitPane.setRightComponent(desktopPane);

    JButton btnNewButton = new JButton("New button");
    btnNewButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {

            DefaultMutableTreeNode  node = new DefaultMutableTreeNode();
            node.setUserObject(new AClass());
            fileTreeModel.insertNodeInto(node, (DefaultMutableTreeNode) rootNode, 0);
            tree.setSelectionPath(new TreePath(fileTreeModel.getPathToRoot(node)));
            tree.expandPath(new TreePath(rootNode.getPath()));
        }
    });
    btnNewButton.setBounds(122, 115, 89, 23);
    desktopPane.add(btnNewButton);

    }

}

AClass.java

public class AClass {

@Override
public String toString() {
    int rand = 5 + (int) (Math.random() * 25);
    return Integer.toString(rand);
    }

}

Answer 1

它們正在改變，因為每次調用toString ，您都在計算一個新的隨機數...

public String toString() {
    int rand = 5 + (int) (Math.random() * 25);
    return Integer.toString(rand);
}

因此，每次表更新時（例如，您單擊它們或以某種方式修改TreeModel時），樹都會向每個節點詢問其值，這將返回一個新的隨機數。

嘗試預先計算值。

node.setUserObject(new AClass(5 + (int) (Math.random() * 25)));

然后只需返回此值...

public String toString() {
    return Integer.toString(rand);
}