为什么我在在线编码 class 代码检查器上收到“线程中的异常”主“java.util.NoSuchElementException”错误？

Question

Every time I run the code on BlueJ, Vscode, and/or Atom it works perfectly fine. However it never works on the code checker.

 import java.util.Scanner;
    import java.lang.Math;

    class Lesson_20_Activity {
    public static void main(String[] args) {
        Scanner scan = new Scanner (System.in);
        
        double fNorth = 0;
        
        double input = 0;
        
        double fSouth = 0;
        
        double fEast = 0;
        
        double fWest = 0;
        
        int cont = 1;
        
        double input2 = 0;
        
        while(cont == 1 ){
            
            System.out.println("Please enter the latitude: ");
            input = scan.nextDouble();
                 
                if(input >=-90.0 && input <= 90.0){
                
                    if(fNorth == 0.0){
                    
                    fNorth = input;
                    
                    fSouth = input;
                    
                  }
                  else{
                    
                    if(input<fSouth){
                        fSouth = input;
                    }
                    else if (input>fNorth){
                        
                        fNorth = input;
                        
                    }          
                 }
                
             }
            
            System.out.println("Please enter the longitude");
            input2 = scan.nextDouble();
            
            if(input2 >= -180.0 && input2 <= 180.0){
                
                if(fWest == 0){
                    
                    fWest = input2;
                    
                    fEast =  input2;
                    
                }
                else{
                    
                    if(input2<fWest){
                        
                        fWest = input2;
                        
                    }
                    
                    else if(input2>fEast){
                        fEast = input2;
                    }
                }
                
            }
            else{
                
                System.out.println("Please enter the longitude:");
            }
            System.out.println("Would you like to enter another location?");
            cont = scan.nextInt();
            
            if(cont == 0){   
                System.out.println("Farthest North: " + fNorth);
            
                System.out.println("Farthest South: " + fSouth);
            
                System.out.println("Farthest East: " + fEast);
            
                System.out.println("Farthest West: " + fWest);
            }
        }

    /*
     * Write your code here Copy and paste your entire program to Code Runner to
     * complete the activity, from the first import statement to the last bracket.
     */
  }
  }

Here's the error that appears:

Exception in thread "main" java.util.NoSuchElementException
        at java.util.Scanner.throwFor(Scanner.java:862)
        at java.util.Scanner.next(Scanner.java:1485)
        at java.util.Scanner.nextDouble(Scanner.java:2413)
        at Lesson_20_Activity.main(Main.java:380)
        at Ideone.assertRegex(Main.java:85)
        at Ideone.assertRegex(Main.java:76)
        at Ideone.test(Main.java:40)
        at Ideone.main(Main.java:29)

I don't know what else to do now. I really need help to resolve this.

Answer 1

In your code, you invoke scan.nextDouble() twice in a row, and thus the line separator is never consumed from the input stream. The first call reads a double, but then the second call looks at the input stream, and since the line separator is still there, but the actual contents of the line was already consumed, it just returns an empty string, which can't be parsed as a double. To solve this problem, just invoke scan.nextLine() in between any calls to scan.nextDouble() or scan.nextInt() . This will consume the line separator characters from the input stream, and allow the scanner to "see" the next line.