NoSuchElementException当使用Scanner对象并在循环中迭代时

Question

当我再次通过for循环时，我正在获取NoSuchElementException。在对代码进行一些更改之前，我能够循环而没有问题。我必须在方法setRiskAmount()中移动用户输入，而不是在此类中使用相同的Scanner对象来读取该输入。那时我开始发现错误。我知道从Scanner没有东西可以读取异常，我只是不确定为什么在这种情况下或如何调整我的代码。

更新： 如果我删除了setRiskAmount()方法中的所有代码，我不再收到错误，并且在我的下一次迭代中，我可以读取用户输入。我以不同的方式来完成它，它工作得很好。为了满足我的应用程序的某些要求，我进行了更改。

@Override 
void setRiskAmount() { 
    // Ask for user input using a Scanner 

    Scanner input = new Scanner(System.in); 
    System.out.print("Please enter risk amount for Property Insurance >> "); 
    riskAmount = input.nextFloat(); 
    input.close(); 
} 

请输入保险类型（房产，汽车，旅游）或quit退出

物业请输入风险金额为财产保险>> 25000 ****** ************物业保险费率为：0.25风险金额为25000.0财产保险费为：6250.0 ***************** *请输入保险类型（Property，Auto，Travel）或退出>>线程“main”中的异常 java.util。 NoSuchElementException异常：没有在在 UseInsurance.main（UseInsurance.java:25） java.util.Scanner.nextLine（来源不明）发现线

public class UseInsurance { 

    public static void main(String[] args) { 
     // The Scanner object will be used for user input 
     Scanner input = new Scanner(System.in); 

     String t = ""; 

     // Create the user interface 
     // Loop will continue looping until the user decides to exit 
     for (int i = 10; i > 0; i++) { 
      System.out.println("Please enter insurance type (Property, Auto, Travel) or QUIT to exit >> "); 
      t = input.nextLine(); 
      if (t.equals("Property")) { 
       // Create an instance of PropertyInsurance, set the object name and type, ask for user input for risk amount 
       // calculate and add to the total quote. Display the results. 

       PropertyInsurance pInsurance = new PropertyInsurance("Property"); 
       pInsurance.setInsuredObjectName(); 
       pInsurance.setRiskAmount(); 
       InsuranceAgentApp.totalPremium += pInsurance.getPremium(); 
       pInsurance.display(); 
      } else if (t.equals("Auto")) { 
       // Create an instance of AutomobileInsurance, set the object name and type, ask for user input for risk amount 
       // calculate and add to the total quote. Display the results. 
       AutomobileInsurance aInsurance = new AutomobileInsurance("Auto"); 
       aInsurance.setInsuredObjectName(); 
       aInsurance.setRiskAmount(); 
       InsuranceAgentApp.totalPremium += aInsurance.getPremium(); 
       aInsurance.display(); 
      } else if (t.equals("Travel")) { 
       // Create an instance of TravelInsurance, set the object name and type, ask for user input for risk amount 
       // calculate and add to the total quote. Display the results. 
       TravelInsurance tInsurance = new TravelInsurance("Travel"); 
       tInsurance.setInsuredObjectName(); 
       tInsurance.setRiskAmount(); 
       InsuranceAgentApp.totalPremium += tInsurance.getPremium(); 
       tInsurance.display(); 
      } else if ((t.equals("QUIT")) || (t.equals("quit")) || (t.equals("Quit"))) { 
       // Exit the loop upon the user typing QUIT, quit or Quit 

       break; 
      } else { 
       // If none of the above options are selected, display a message 
       // and loop again. 

       System.out.println("Invalid input"); 
      } 
     } 

     // Display the amount of the total quote 
     System.out.println("The total quote is " + InsuranceAgentApp.totalPremium); 
     // Close the Scanner object 
     input.close(); 

    } 

} 

Answer 1

问题出在setRiskAmount()。当您从System.in中关闭Scanner读数时，它不仅会关闭该特定的Scanner，还会关闭System.in。这可以防止主方法中的Scanner读取System.in的任何其他输入。

解决方法是简单地删除关闭此线的线Scanner。如果您有任何可能需要在代码中稍后从System.in读取任何输入，则永远不应该从System.in关闭Scanner读数。

Answer 2

问题是您在报价后关闭输入，只需删除该行。此外，我还包含了一些可能对您更好的代码，因为它更干净，更加稳固。我留下评论来解释我做了什么。

 Boolean done = false; //Boolean variable to monitor loop without increments 

     // Create the user interface 
     // Loop will continue looping until the user decides to exit 
     while(!done){ 
      System.out.println("Please enter insurance type (Property, Auto, Travel) or QUIT to exit >> "); 
      t = input.nextLine(); 
      t = t.toUpperCase();//normalizes the string to all upercase letters 
      switch(t){ 
       case "PROPERTY": 
        //your code 
       case "AUTO": 
        //your code 
       case "TRAVEL": 
        //your code 
       case "QUIT": 
        done = true;//loop wil exit when done is true 

       default: 
        System.out.println("Invalid Input"); 
        } 


     } 

Answer 3

public class Test { 
static float riskAmount; 
static Scanner input = new Scanner(System.in); 
public static void main(String[] args) { 
    for (int i = 0; i < 10; i++) { 
     setRiskAmount(); 
     if(i==9){ 
      System.out.println("Total Risk Amount is: "+ riskAmount); 
     } 
    } 
} 
static void setRiskAmount() { 
    System.out.print("Please enter risk amount for Property Insurance >> "); 
    riskAmount+= input.nextFloat(); 
} } 

我为你做它会工作1000％。只需要将扫描仪声明为全局。

Answer 4

public class Test { 
static float riskAmount; 
static Scanner input = new Scanner(System.in); 
public static void main(String[] args) { 
    for (int i = 0; i < 10; i++) { 
     setRiskAmount(); 
     if(i==9){ 
      System.out.println("Total Risk Amount is: "+ riskAmount); 
      input.close(); 
     } 
    } 
} 
static void setRiskAmount() { 
    System.out.print("Please enter risk amount for Property Insurance >> "); 
    riskAmount+= input.nextFloat(); 
} }