我想显示一棵树。 但树并没有出现。 有什么问题吗？
主要:
package scanner_parser;
public class Main {
public static void main(String[] args) {
Oberflaeche gui = new Oberflaeche();
gui.setVisible(true);
}
}
图形用户界面:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.*;
import javax.swing.*;
public class Oberflaeche extends JFrame implements ActionListener {
private JPanel cp, top, bottom;
private JTextField eingabefeld = new JTextField();
private JButton button = new JButton("Darstellen");
private JMenuBar menubar = new JMenuBar();
private JMenu menu;
private JMenuItem anleitung, beenden, bEins, bZwei, bDrei, bVier;
private Baum baum = new Baum();
public Oberflaeche() {
this.setTitle("Funktionsparser");
this.setSize(900, 700);
this.setLocation(300, 100);
this.setResizable(true);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
initMenu();
cp = (JPanel) this.getContentPane();
cp.setLayout(new BorderLayout(2, 1));
top = new JPanel();
top.setLayout(null);
top.setBounds(0, 0, getWidth(), 50);
top.setBackground(Color.white);
bottom = new JPanel();
bottom.setBounds(0, 50, getWidth(), getHeight() - 50);
bottom.setBackground(Color.white);
eingabefeld.setBounds(10, 10, getWidth() - 120, 30);
button.setBounds(getWidth() - 110, 10, 100, 30);
button.addActionListener(this);
top.add(button);
top.add(eingabefeld);
cp.add(top);
cp.add(bottom);
}
// Initialise Menu
private void initMenu() {
menu = new JMenu("Datei");
anleitung = new JMenuItem("Anleitung");
anleitung.addActionListener(this);
menu.add(anleitung);
beenden = new JMenuItem("Beenden");
beenden.addActionListener(this);
menu.add(beenden);
menubar.add(menu);
menu = new JMenu("Beispiele");
// Load some example functions into the textfield
bEins = new JMenuItem("<html>3 * x</html>");
bEins.addActionListener(this);
menu.add(bEins);
bZwei = new JMenuItem("<html>3 * x<sup>2</sup></html>");
bZwei.addActionListener(this);
menu.add(bZwei);
bDrei = new JMenuItem("<html>3 * ( x<sup>2</sup> + 1 )</html>");
bDrei.addActionListener(this);
menu.add(bDrei);
bVier = new JMenuItem("<html>3 * ( x<sup>2</sup> + x<sup>4</sup> + 1 )</html>");
bVier.addActionListener(this);
menu.add(bVier);
menubar.add(menu);
this.setJMenuBar(menubar);
}
@Override
public void actionPerformed(ActionEvent e) {
Object s = e.getSource();
if (s == anleitung) {
}
// This should add the tree (baum) but it does not appear.
if (s == button) {
FuncParser.theParser().parse(eingabefeld.getText());
FuncParser.theParser().getWurzel().print();
bottom.add(baum);
}
if (s == beenden) {
System.exit(0);
}
if (s == bEins) {
eingabefeld.setText("3*x");
}
if (s == bZwei) {
eingabefeld.setText("3*x^2");
}
if (s == bDrei) {
eingabefeld.setText("3*(x^2+1)");
}
if (s == bVier) {
eingabefeld.setText("3*(x^2+x^4+1)");
}
}
}
树类:
import java.awt.*;
import javax.swing.JPanel;
public class Baum extends JPanel {
private final int radius = 20;
private final int paddingY = 75;
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
System.out.println("test");
displayBaum(g, FuncParser.theParser().getWurzel(), getWidth() / 2, 100, 20 + getWidth() / 4);
}
private void displayBaum(Graphics g, Knoten k, int x, int y, int paddingX) {
g.drawOval(x - radius, y - radius, 2 * radius, 2 * radius);
g.drawString(k.getDaten(), x - 4, y + 4);
if (k.getLinks() != null) {
displayKante(g, x - paddingX, y + paddingY, x, y);
displayBaum(g, k.getLinks(), x - paddingX, y + paddingY, 10 + paddingX / 2);
displayKante(g, x + paddingX, y + paddingY, x, y);
displayBaum(g, k.getLinks(), x + paddingX, y + paddingY, 10 + paddingX / 2);
}
}
private void displayKante(Graphics g, int x1, int y1, int x2, int y2) {
double d = Math.sqrt(paddingY * paddingY + (x2 - x1) * (x2 - x1));
int x11 = (int) (x1 - radius * (x1 - x2) / d);
int y11 = (int) (y1 - radius * (y1 - y2) / d);
int x21 = (int) (x2 + radius * (x1 - x2) / d);
int y21 = (int) (y2 + radius * (y1 - y2) / d);
g.drawLine(x11, y11, x21, y21);
}
}
每次缩放窗口时，控制台中都会出现文本“test”。 这意味着该函数被调用，但树不会出现在内容 Pane 上。也许它下面有什么东西？我现在不明白为什么。如果您有想法，请帮忙。
最佳答案
将片段减少到可编译状态，我得到以下结果。特别是，
不要使用
null布局；该示例对JFrame使用默认的BorderLayout，对Panel使用默认的FlowLayout。使用
JTextField构造函数，可让您以列为单位指定字段的宽度。覆盖
getPreferredSize()建立绘图区域的初始几何形状，并相对于其当前尺寸进行绘制。仅在 event dispatch thread 上构造和操作 Swing GUI 对象.
在
ActionListener中优先使用equals()而不是==。
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JTextField;
/**
* @See https://stackoverflow.com/a/38215252/230513
*/
public class Main {
public static void main(String[] args) {
EventQueue.invokeLater(() -> {
Oberflaeche gui = new Oberflaeche();
gui.setVisible(true);
});
}
private static class Baum extends JPanel {
private final int radius = 20;
private final int paddingY = 75;
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawString("Hello", 16, 16);
displayKante(g, 0, 0, getWidth(), getHeight());
}
@Override
public Dimension getPreferredSize() {
return new Dimension(329, 240);
}
private void displayKante(Graphics g, int x1, int y1, int x2, int y2) {
double d = Math.sqrt(paddingY * paddingY + (x2 - x1) * (x2 - x1));
int x11 = (int) (x1 - radius * (x1 - x2) / d);
int y11 = (int) (y1 - radius * (y1 - y2) / d);
int x21 = (int) (x2 + radius * (x1 - x2) / d);
int y21 = (int) (y2 + radius * (y1 - y2) / d);
g.drawLine(x11, y11, x21, y21);
}
}
private static class Oberflaeche extends JFrame implements ActionListener {
private JPanel top, bottom;
private JTextField eingabefeld = new JTextField(20);
private JButton button = new JButton("Darstellen");
private JMenuBar menubar = new JMenuBar();
private JMenu menu;
private JMenuItem anleitung, beenden, bEins, bZwei, bDrei, bVier;
private Baum baum = new Baum();
public Oberflaeche() {
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
this.setTitle("Funktionsparser");
initMenu();
top = new JPanel();
top.setBackground(Color.white);
top.add(button);
top.add(eingabefeld);
button.addActionListener(this);
bottom = new JPanel();
bottom.setBackground(Color.white);
bottom.add(new JLabel("Label text."));
this.add(top, BorderLayout.NORTH);
this.add(baum);
this.add(bottom, BorderLayout.SOUTH);
this.pack();
this.setLocationRelativeTo(null);
}
// Initialise Menu
private void initMenu() {
menu = new JMenu("Datei");
anleitung = new JMenuItem("Anleitung");
anleitung.addActionListener(this);
menu.add(anleitung);
beenden = new JMenuItem("Beenden");
beenden.addActionListener(this);
menu.add(beenden);
menubar.add(menu);
menu = new JMenu("Beispiele");
// Load some example functions into the textfield
bEins = new JMenuItem("<html>3 * x</html>");
bEins.addActionListener(this);
menu.add(bEins);
bZwei = new JMenuItem("<html>3 * x<sup>2</sup></html>");
bZwei.addActionListener(this);
menu.add(bZwei);
bDrei = new JMenuItem("<html>3 * ( x<sup>2</sup> + 1 )</html>");
bDrei.addActionListener(this);
menu.add(bDrei);
bVier = new JMenuItem("<html>3 * ( x<sup>2</sup> + x<sup>4</sup> + 1 )</html>");
bVier.addActionListener(this);
menu.add(bVier);
menubar.add(menu);
this.setJMenuBar(menubar);
}
@Override
public void actionPerformed(ActionEvent e) {
Object s = e.getSource();
if (s == anleitung) {
System.out.println(anleitung);
}
if (s == button) {
System.out.println(button);
}
if (s == beenden) {
System.exit(0);
}
if (s == bEins) {
eingabefeld.setText("3*x");
}
if (s == bZwei) {
eingabefeld.setText("3*x^2");
}
if (s == bDrei) {
eingabefeld.setText("3*(x^2+1)");
}
if (s == bVier) {
eingabefeld.setText("3*(x^2+x^4+1)");
}
}
}
}
关于java - 绘制树不可见；可能是布局问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38209846/