找不到符号-变量

Question

I'm new to Java, and I'm trying to get user input, store each line of input as a variable and then return each value so that it can be passed on somewhere else. When I try and compile it is telling me that it can't find the variable magnitude. I'm assuming it won't find the others either. I'm guessing that this is because I've declare the variables inside of the "try" but don't know how to get it so that the return statement accepts them. Code is as follows:

 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

You are declaring magnitude inside the try block.

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

so you have to declare it outside the try:

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

You have to define the variable outside of your try-catch. Same goes for the other variables you want to use outside the try-catch.

Answer 3

The variables which are created in the try block are local variables . They just exist inside the try block and so they are not accessible from outside. If you declare the variable above the try block, you can access it in and outside of the try block.

Answer 4

try this

  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

Declare it outside of the try block, even if it's null..

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

Answer 6

just declare magnitude variable globally i think problem get solves

you declared that variable inside the try block and trying to access that variable out side of try.that is the reason it is raising the error as cannot find symbol.