找不到符號 - 變量

我是Java的新手，我試圖獲取用戶輸入，將每行輸入存儲爲變量，然後返回每個值，以便可以將其傳遞到其他位置。當我嘗試編譯時，它告訴我它無法找到變量幅度。我假設它不會找到其他人。我猜這是因爲我已經聲明瞭「try」中的變量，但不知道如何獲取它，以便return語句接受它們。代碼如下：找不到符號 - 變量

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); 
}

來源

2013-10-31 Ben Garside

如果您想在外部使用它們，請不要在'try'塊中聲明變量。 – Maroun

您必須定義try-catch之外的變量。您想在try-catch之外使用的其他變量也一樣。

來源

2013-10-31 09:47:49

你正在try塊中聲明幅度。

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

所以你必須聲明它的嘗試外：

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); 
}

來源

2013-10-31 09:48:30 RamonBoza

對，這真的很有幫助謝謝 –

嘗試這是在try塊創建此

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); 
     }

來源

2013-10-31 09:49:47 Nambi

如果你返回的東西至少要初始化爲'null' – Dropout

的變量是local variables。它們只存在於try塊內，因此它們不能從外部訪問。如果你在try塊上面聲明變量，你可以在try塊內外訪問它。

來源

2013-10-31 09:50:28 Akkusativobjekt

謝謝，這是唯一的答案，提供了一些關於範圍界定的額外解釋。 – Geekfish

聲明它try塊之外，即使是空..

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

來源

2013-10-31 09:50:58 Dropout

只是聲明幅度全局變量來，我認爲問題的get解決

你宣稱try塊內的變量，並試圖訪問try.that這個變量，這就是它提出錯誤的原因，因爲找不到符號。

來源

2013-10-31 09:54:35 Raj

找不到符號 - 變量

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