Java 如何在滚动窗格上放置多个标签?为什么将此标签放置在中心?
我正在尝试制作一个提要框,其中显示从服务器到客户端的所有更新。在Java 如何在滚动窗格上放置多个标签?为什么将此标签放置在中心?,java,swing,Java,Swing,我正在尝试制作一个提要框,其中显示从服务器到客户端的所有更新。在Jframe上,我放置了一个JScrollPane,以便客户端可以轻松看到更多的提要 在JScrollPane上,我试图放置一个JLabel,然后它看起来像这样: 标签被放置在中间,如果我试图放置一个新的JLabel,尽管IDE的导航窗口显示,它已经被放置,但我看不到它。默认情况下,封闭的JFrame的布局已设置为自由设计。我试着改变流量布局,但没有帮助 为什么JLabel被放置在窗口的中心?这是从服务器向客户端显示提要的正确方式
Jframe
上,我放置了一个JScrollPane
,以便客户端可以轻松看到更多的提要
在JScrollPane
上,我试图放置一个JLabel
,然后它看起来像这样:
标签被放置在中间,如果我试图放置一个新的JLabel
,尽管IDE的导航窗口显示,它已经被放置,但我看不到它。默认情况下,封闭的JFrame
的布局已设置为自由设计。我试着改变流量布局,但没有帮助
为什么JLabel
被放置在窗口的中心?这是从服务器向客户端显示提要的正确方式吗?讨论的内容将RSS提要中的条目添加到JTextPane
。我在下面举例说明了一种变化
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.net.URL;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.CharacterData;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
/**
* @see https://stackoverflow.com/a/19164649/230513
* @see https://stackoverflow.com/q/10461087/230513
*/
public class NewsFeed extends JPanel {
public NewsFeed() {
this.setLayout(new GridLayout());
JTextPane newsPane = new JTextPane();
newsPane.setContentType("text/html");
newsPane.setEditable(false);
JScrollPane scrollPane = new JScrollPane(newsPane);
scrollPane.setVerticalScrollBarPolicy(
javax.swing.ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
RSS reader = RSS.getInstance();
String rssNews = reader.writeNews();
newsPane.setText(rssNews);
this.add(scrollPane);
}
public static void main(String args[]) {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
JFrame f = new JFrame("News");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new NewsFeed());
f.pack();
f.setSize(640, 480);
f.setLocationRelativeTo(null);
f.setVisible(true);
}
});
}
private static class RSS {
private static final String NAME =
"http://thestar.com.my.feedsportal.com/c/33048/f/534600/index.rss";
private static RSS instance = null;
public static RSS getInstance() {
if (instance == null) {
instance = new RSS();
}
return instance;
}
public String writeNews() {
String result = "";
try {
DocumentBuilder builder = DocumentBuilderFactory
.newInstance().newDocumentBuilder();
URL u = new URL(NAME);
Document doc = builder.parse(u.openStream());
NodeList nodes = doc.getElementsByTagName("item");
for (int i = 0; i < nodes.getLength(); i++) {
Element element = (Element) nodes.item(i);
result += "Title: " + getElementValue(element, "title") + "<br>";
result += "Link: " + getElementValue(element, "link") + "<br>";
result += "Publish Date: " + getElementValue(element, "pubDate") + "<br>";
result += "Description: " + getElementValue(element, "description") + "<br>";
}
} catch (Exception ex) {
ex.printStackTrace(System.err);
}
return result;
}
private String getCharacterDataFromElement(Element e) {
try {
Node child = e.getFirstChild();
if (child instanceof CharacterData) {
CharacterData cd = (CharacterData) child;
return cd.getData();
}
} catch (Exception ex) {
ex.printStackTrace(System.err);
}
return "";
}
protected float getFloat(String value) {
if (value != null && !value.equals("")) {
return Float.parseFloat(value);
}
return 0;
}
protected String getElementValue(Element parent, String label) {
return getCharacterDataFromElement(
(Element) parent.getElementsByTagName(label).item(0));
}
}
}
导入java.awt.EventQueue;
导入java.awt.GridLayout;
导入java.net.URL;
导入javax.swing.JFrame;
导入javax.swing.JPanel;
导入javax.swing.JScrollPane;
导入javax.swing.JTextPane;
导入javax.xml.parsers.DocumentBuilder;
导入javax.xml.parsers.DocumentBuilderFactory;
导入org.w3c.dom.CharacterData;
导入org.w3c.dom.Document;
导入org.w3c.dom.Element;
导入org.w3c.dom.Node;
导入org.w3c.dom.NodeList;
/**
*@见https://stackoverflow.com/a/19164649/230513
*@见https://stackoverflow.com/q/10461087/230513
*/
公共类新闻提要扩展了JPanel{
公共新闻提要(){
this.setLayout(新的GridLayout());
JTextPane newsPane=新的JTextPane();
setContentType(“text/html”);
newsPane.setEditable(false);
JScrollPane scrollPane=新的JScrollPane(新闻窗格);
scrollPane.setVerticalScrollBarPolicy(
javax.swing.ScrollPaneConstants.VERTICAL\u SCROLLBAR\u ALWAYS);
RSS reader=RSS.getInstance();
字符串rssNews=reader.writeNews();
newsPane.setText(rssNews);
添加(滚动窗格);
}
公共静态void main(字符串参数[]){
invokeLater(新的Runnable(){
@凌驾
公开募捐{
JFrame f=新JFrame(“新闻”);
f、 setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f、 添加(NewsFeed());
f、 包装();
f、 设置大小(640480);
f、 setLocationRelativeTo(空);
f、 setVisible(真);
}
});
}
私有静态类RSS{
私有静态最终字符串名=
"http://thestar.com.my.feedsportal.com/c/33048/f/534600/index.rss";
私有静态RSS实例=null;
公共静态RSS getInstance(){
if(实例==null){
instance=newrss();
}
返回实例;
}
公共字符串writeNews(){
字符串结果=”;
试一试{
DocumentBuilder=DocumentBuilderFactory
.newInstance().newDocumentBuilder();
URL u=新的URL(名称);
documentdoc=builder.parse(u.openStream());
NodeList节点=doc.getElementsByTagName(“项”);
对于(int i=0;i”;
结果+=“链接:”+getElementValue(元素,“链接”)+“
”;
结果+=“发布日期:”+getElementValue(元素,“发布日期”)+“
”;
结果+=“描述:”+getElementValue(元素,“描述”)+“
”;
}
}捕获(例外情况除外){
例如printStackTrace(System.err);
}
返回结果;
}
私有字符串getCharacterDataFromElement(元素e){
试一试{
Node child=e.getFirstChild();
if(CharacterData的子实例){
CharacterData cd=(CharacterData)子级;
返回cd.getData();
}
}捕获(例外情况除外){
例如printStackTrace(System.err);
}
返回“”;
}
受保护的浮点getFloat(字符串值){
if(value!=null&&!value.equals(“”){
返回Float.parseFloat(值);
}
返回0;
}
受保护的字符串getElementValue(元素父级,字符串标签){
返回getCharacterDataFromElement(
(Element)parent.getElementsByTagName(label.item(0));
}
}
}
讨论的方法将RSS提要中的条目添加到JTextPane
。我在下面举例说明了一种变化
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.net.URL;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.CharacterData;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
/**
* @see https://stackoverflow.com/a/19164649/230513
* @see https://stackoverflow.com/q/10461087/230513
*/
public class NewsFeed extends JPanel {
public NewsFeed() {
this.setLayout(new GridLayout());
JTextPane newsPane = new JTextPane();
newsPane.setContentType("text/html");
newsPane.setEditable(false);
JScrollPane scrollPane = new JScrollPane(newsPane);
scrollPane.setVerticalScrollBarPolicy(
javax.swing.ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
RSS reader = RSS.getInstance();
String rssNews = reader.writeNews();
newsPane.setText(rssNews);
this.add(scrollPane);
}
public static void main(String args[]) {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
JFrame f = new JFrame("News");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new NewsFeed());
f.pack();
f.setSize(640, 480);
f.setLocationRelativeTo(null);
f.setVisible(true);
}
});
}
private static class RSS {
private static final String NAME =
"http://thestar.com.my.feedsportal.com/c/33048/f/534600/index.rss";
private static RSS instance = null;
public static RSS getInstance() {
if (instance == null) {
instance = new RSS();
}
return instance;
}
public String writeNews() {
String result = "";
try {
DocumentBuilder builder = DocumentBuilderFactory
.newInstance().newDocumentBuilder();
URL u = new URL(NAME);
Document doc = builder.parse(u.openStream());
NodeList nodes = doc.getElementsByTagName("item");
for (int i = 0; i < nodes.getLength(); i++) {
Element element = (Element) nodes.item(i);
result += "Title: " + getElementValue(element, "title") + "<br>";
result += "Link: " + getElementValue(element, "link") + "<br>";
result += "Publish Date: " + getElementValue(element, "pubDate") + "<br>";
result += "Description: " + getElementValue(element, "description") + "<br>";
}
} catch (Exception ex) {
ex.printStackTrace(System.err);
}
return result;
}
private String getCharacterDataFromElement(Element e) {
try {
Node child = e.getFirstChild();
if (child instanceof CharacterData) {
CharacterData cd = (CharacterData) child;
return cd.getData();
}
} catch (Exception ex) {
ex.printStackTrace(System.err);
}
return "";
}
protected float getFloat(String value) {
if (value != null && !value.equals("")) {
return Float.parseFloat(value);
}
return 0;
}
protected String getElementValue(Element parent, String label) {
return getCharacterDataFromElement(
(Element) parent.getElementsByTagName(label).item(0));
}
}
}
导入java.awt.EventQueue;
导入java.awt.GridLayout;
导入java.net.URL;
导入javax.swing.JFrame;
导入javax.swing.JPanel;
导入javax.swing.JScrollPane;
导入javax.swing.JTextPane;
导入javax.xml.parsers.DocumentBuilder;
导入javax.xml.parsers.DocumentBuilderFactory;
导入org.w3c.dom.CharacterData;
导入org.w3c.dom.Document;
导入org.w3c.dom.Element;
导入org.w3c.dom.Node;
导入org.w3c.dom.NodeList;
/**
*@见https://stackoverflow.com/a/19164649/230513
*@见https://stackoverflow.com/q/10461087/230513
*/
公共类新闻提要扩展了JPanel{
公共新闻提要(){
this.setLayout(新的GridLayout());
JTextPane newsPane=新的JTextPane();
setContentType(“text/html”);
newsPane.setEditable(false);
JScrollPane scrollPane=新的JScrollPane(新闻窗格);
scrollPane.setVerticalScrollBarPolicy(
javax.swing.ScrollPaneConstants.VERTICAL\u SCROLLBAR\u ALWAYS);
RSS reader=RSS.getInstance();
字符串rs