Question

我试图将readLine（）输出保存到变量（它只包含一行），以便将来比较这些行。但变量不会改变它们的值：

try {
                        String VersName = "src/bin/version.txt";
                        BufferedReader br = null;
                        br = new BufferedReader(new FileReader(VersName));
                        URL url = new URL("ftp://31.130.206.175/current_versions/vers");

                        // read text returned by server
                        BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
                        System.out.println(br.readLine());
                        System.out.println(in.readLine());

                        String aa = null;
                        String bb = null;
                        aa = br.readLine();
                        bb = in.readLine();
                        System.out.println("***" + aa + "***" + bb + "***");

                        in.close();
                        br.close();

                    } catch (MalformedURLException e3) {
                        System.out.println("Malformed URL");
                    } catch (IOException e4) {
                        System.out.println("I/O Error");
                    }

输出：

0.0.0
0.1.0
***null***null***

当我试图将它们转换为字符串（aa = br.readLine（）。toString（）;）时，我有一个例外：

0.0.0
0.1.0
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at Launcher.SimpleSwingBrowser$3.actionPerformed(SimpleSwingBrowser.java:209)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6535)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6300)
    at java.awt.Container.processEvent(Container.java:2236)
    at java.awt.Component.dispatchEventImpl(Component.java:4891)
    at java.awt.Container.dispatchEventImpl(Container.java:2294)
    at java.awt.Component.dispatchEvent(Component.java:4713)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
    at java.awt.Container.dispatchEventImpl(Container.java:2280)
    at java.awt.Window.dispatchEventImpl(Window.java:2750)
    at java.awt.Component.dispatchEvent(Component.java:4713)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.awt.EventQueue$4.run(EventQueue.java:729)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

有没有办法将它们保存到变量？

谢谢。

Answer 1

你的问题在这里

System.out.println(br.readLine());
System.out.println(in.readLine());

您阅读了自己的行，因此

不再可用

aa = br.readLine();
bb = in.readLine();

所以你什么都不读。

尝试重新排序您的说明（例如）：

String aa = br.readLine();
String bb = in.readLine();

System.out.println(aa);
System.out.println(bb);

应该更好;）

无法保存readLine（）;到字符串变量

1 个答案: