错误扫描文本文件显示错误“线程异常 "AWT-EventQueue-0" java.util.NoSuchElementException”

Question

public class checkDuplicateNames1 {



public boolean checkDuplicateNames1(String name , String surname){
   boolean found = false;
    File file = new File("transactions.txt");

    try {
        Scanner sc = new Scanner(new File("transactions.txt"));
        sc.useDelimiter("/");


        while(sc.hasNext()){

        String userName = sc.next();
        String userLastName = sc.next();
        String userCash = sc.next();
        String paidStatus = sc.next();

        if((userName.equals(name)&&userLastName.equals(surname))){

            found = true;

        }
        else
        {

            found = false;
        }
        }

    } catch (FileNotFoundException ex) {
        Logger.getLogger(checkDuplicateNames.class.getName()).log(Level.SEVERE, null, ex);
    }






 return found;



}

}

当我使用 "boolean checkDuplicateNames1" 方法时，出现此错误

Exception in thread "AWT-EventQueue-0" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:862)
at java.util.Scanner.next(Scanner.java:1371)
at Lending.checkDuplicateNames1.checkDuplicateNames1(checkDuplicateNames1.java:41)
at Lending.Loan.jButton1ActionPerformed(Loan.java:250)
at Lending.Loan.access0(Loan.java:24)
at Lending.Loan.actionPerformed(Loan.java:137)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6533)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6298)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access0(EventQueue.java:97)
at java.awt.EventQueue.run(EventQueue.java:709)
at java.awt.EventQueue.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue.run(EventQueue.java:731)
at java.awt.EventQueue.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$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)

我试过使用不同的文件读取器，比如 bufferedReader，它是一样的，

这里是使用"checDuplicateNames1"方法的"Loan class "方法

 private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         

    // TODO add your handling code here:


    String name = jTextField1.getText();
    String surname = jTextField4.getText();
    String cash = jTextField5.getText();
    System.out.println("loan clicked");

    try {

        String info = name + "/" + surname + "/" + cash + "/" + "unpaid";

        checkDuplicateNames1 c = new checkDuplicateNames1();
        boolean duplicated = c.checkDuplicateNames1(name,surname);

        if(duplicated == true){
            System.out.println("duplicated");
            this.currentName = name;
            this.currentSurname = surname;
          JOptionPane.showMessageDialog(null,"Person already in the Record ");
          wannaAddLoanValue w = new wannaAddLoanValue(name,surname,cash);
          w.show();



        }
        else
        {
            File file = new File("transactions.txt");
             PrintWriter writer = new PrintWriter(new FileWriter(file,true));
             String info1 = name + "/" + surname + "/" + cash + "/" + "unpaid";
             writer.println(info1); 
              writer.close();

        }



    } catch (FileNotFoundException ex) {
        Logger.getLogger(Loan.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IOException ex) {
        Logger.getLogger(Loan.class.getName()).log(Level.SEVERE, null, ex);
    }




}

并且文件中的文本也是这样的

rodchris/toledo/200/unpaid
yannie/taub/890/unpaid

Answer 1

您应该始终在 sc.next(); 之前调用 sc.hasNext()。

while(sc.hasNext()){

    // This line is OK
    String userName = sc.next();

    // The following lines can cause NoSuchElementException
    String userLastName = sc.next();
    String userCash = sc.next();
    String paidStatus = sc.next();

checkDuplicateNames1()可以重构为：

public boolean checkDuplicateNames1(String name, String surname) {
    boolean found = false;
    try (Scanner sc = new Scanner(new File("transactions.txt"))) {
        sc.useDelimiter("/");
        String userName = sc.hasNext() ? sc.next() : null;
        String userLastName = sc.hasNext() ? sc.next() : null;
        return userName != null && userLastName != null && userName.equals(name) && userLastName.equals(surname);            
    } catch (FileNotFoundException ex) {
        Logger.getLogger(checkDuplicateNames.class.getName()).log(Level.SEVERE, null, ex);
    }
    return found;
}

Answer 2

你 class 中的哪一行是 41 ？即 next() 导致错误，

我认为 hasNext() 将整个当前输入视为 1 个标记，但是当你多次调用 next() 时，你只得到第一个 1 然后是异常，要解决这个问题我认为你必须在每个 next()

之前检查 hasNext()

while(sc.hasNext()){
    String userName="",userLastName="",userCash="",paidStatus="";

    //first one already checked in while(...)
    userName = sc.next();

    if(sc.hasNext())        
        userLastName = sc.next();

    if(sc.hasNext())
        userCash = sc.next();

    if(sc.hasNext())
        paidStatus = sc.next();

    //... rest of code

在其余代码中，您可能需要检查每个变量是否为空

if(!userLastName.isEmpty()) ...

错误扫描文本文件显示错误“线程异常 "AWT-EventQueue-0" java.util.NoSuchElementException”

ERROR Scanning textFile shows error " Exception in thread "AWT-EventQueue-0" java.util.NoSuchElementException"

java

swing

text-files

bufferedreader

java.util.scanner