找不到符号-变量

Question

我是Java的新手，我正在尝试获取用户输入，将输入的每一行存储为变量，然后返回每个值，以便可以将其传递到其他地方。 当我尝试编译时，它告诉我找不到可变的幅度。 我假设它也找不到其他人。 我猜这是因为我已经在“ try”中声明了变量，但是不知道如何获取变量，以便return语句接受它们。 代码如下：

 public Earthquake userAddEarthquake()
    {

        Scanner scanner = new Scanner(System.in);
        try{
            // convert the string read from the scanner into Integer type
            System.out.println("Please Enter An Earthquake Magnitude: ");
            Double magnitude = Double.parseDouble(scanner.nextLine());
            System.out.println("Please Enter The Earthquakes Latitude Position: ");
            scanner = new Scanner(System.in);
            Double positionLatitude = Double.parseDouble(scanner.nextLine()); 
            System.out.print("Please Enter The Earthquakes Longitude Position: ");
            scanner = new Scanner(System.in);
            Double positionLongitude = Double.parseDouble(scanner.nextLine()); 
            System.out.print("Please Enter The Year That The Earthquake Occured: ");
            scanner = new Scanner(System.in);
            int year = Integer.parseInt(scanner.nextLine()); 
            System.out.println("Magnitude = " + magnitude);
    }  

    catch(NumberFormatException ne){
            System.out.println("Invalid Input");
        }
        finally{
            scanner.close();

        }

     return new Earthquake(magnitude, positionLatitude, positionLongitude, year);   
}

Answer 1

您在try块内声明了幅度。

try {
    Double magnitude
    //magnitude will only be visible inside try block
}

因此，您必须在尝试之外声明它：

public Earthquake userAddEarthquake() {

    Scanner scanner = new Scanner(System.in);
    Double magnitude = Double.MIN_VALUE; //with a default value
    try{
        // convert the string read from the scanner into Integer type
        System.out.println("Please Enter An Earthquake Magnitude: ");
        magnitude = Double.parseDouble(scanner.nextLine());
        System.out.println("Please Enter The Earthquakes Latitude Position: ");
        scanner = new Scanner(System.in);
        Double positionLatitude = Double.parseDouble(scanner.nextLine()); 
        System.out.print("Please Enter The Earthquakes Longitude Position: ");
        scanner = new Scanner(System.in);
        Double positionLongitude = Double.parseDouble(scanner.nextLine()); 
        System.out.print("Please Enter The Year That The Earthquake Occured: ");
        scanner = new Scanner(System.in);
        int year = Integer.parseInt(scanner.nextLine()); 
        System.out.println("Magnitude = " + magnitude);
}  

catch(NumberFormatException ne){
        System.out.println("Invalid Input");
    }
    finally{
        scanner.close();

    }

 return new Earthquake(magnitude, positionLatitude, positionLongitude, year);   
}

Answer 2

您必须在try-catch之外定义变量。 您想在try-catch之外使用的其他变量也是如此。

Answer 3

在try块中创建的变量是local variables 。 它们仅存在于try块内部，因此无法从外部访问它们。 如果在try块上方声明变量，则可以在try块内外访问它。

Answer 4

尝试这个

  Double magnitude=null ;
     Double positionLatitude=null;
     Double positionLongitude=null;
    int year;
    try{
                // convert the string read from the scanner into Integer type
                System.out.println("Please Enter An Earthquake Magnitude: ");
              magnitude  = Double.parseDouble(scanner.nextLine());
                System.out.println("Please Enter The Earthquakes Latitude Position: ");
                scanner = new Scanner(System.in);
              positionLatitude = Double.parseDouble(scanner.nextLine()); 
                System.out.print("Please Enter The Earthquakes Longitude Position: ");
                scanner = new Scanner(System.in);
             positionLongitude = Double.parseDouble(scanner.nextLine()); 
                System.out.print("Please Enter The Year That The Earthquake Occured: ");
                scanner = new Scanner(System.in);
                year = Integer.parseInt(scanner.nextLine()); 
                System.out.println("Magnitude = " + magnitude);
        }  

Answer 5

在try块之外声明它，即使它为null。

Double magnitude = null;
try{
    // ...
    magnitude = Double.parseDouble(scanner.nextLine());
    // ...
}catch{
    // ...
}
return magnitude;

Answer 6

只是在全球范围内声明幅度变量，我认为问题可以解决

您在try块中声明了该变量，并尝试在try之外访问该变量。这就是由于找不到符号而引发错误的原因。