Java：局部变量范围

Question

我得到一个错误，说编译器找不到我的变量“complexArray”，但我不知道为什么。如何修复我的程序，使其返回从文件中读取的复数数组？

public static Complex[] parseFromFile(String fileName) { 
    int numOfComplex = 0; 
    try { 
     Scanner sc = new Scanner(new File(fileName)); 
     String firstLine = sc.nextLine(); 
     firstLine = firstLine.trim(); 
     numOfComplex = Integer.parseInt(firstLine); 
     Complex[] complexArray = new Complex[numOfComplex]; 
     for (int i = 0; i < numOfComplex; i++) { 
      String nextLine = sc.nextLine(); 
      nextLine = nextLine.trim(); 
      complexArray[i] = parseComplex(nextLine); 
     } 
    } 
    catch(Exception e) { 
    } 
    return complexArray; 
} 

Answer 1

您的complexArray变量在try {}范围内声明。在try语句之前声明它。

Complex [] complexArray = null;因为complexArray在try {}语句

public static Complex[] parseFromFile(String fileName) { 
int numOfComplex = 0; 
try { 
    Scanner sc = new Scanner(new File(fileName)); 
    String firstLine = sc.nextLine(); 
    firstLine = firstLine.trim(); 
    numOfComplex = Integer.parseInt(firstLine); 
    Complex[] complexArray = new Complex[numOfComplex]; 
    for (int i = 0; i < numOfComplex; i++) { 
     String nextLine = sc.nextLine(); 
     nextLine = nextLine.trim(); 
     complexArray[i] = parseComplex(nextLine); 
    } 
return complexArray; 
} 
catch(Exception e) { 
} 

}

Answer 2

认沽回报complexArray语句在try块中声明，一旦try块内执行完毕complexArray超出范围。

 public static Complex[] parseFromFile(String fileName) { 
     int numOfComplex = 0; 
     try { 
      Scanner sc = new Scanner(new File(fileName)); 
      String firstLine = sc.nextLine(); 
      firstLine = firstLine.trim(); 
      numOfComplex = Integer.parseInt(firstLine); 
      Complex[] complexArray = new Complex[numOfComplex]; 
      for (int i = 0; i < numOfComplex; i++) { 
       String nextLine = sc.nextLine(); 
       nextLine = nextLine.trim(); 
       complexArray[i] = parseComplex(nextLine); 
      } 
     } //<<<=== scope of `complexArray` ends here 
     catch(Exception e) { 
     } 
     return complexArray; 
    } 

试试这个

 public static Complex[] parseFromFile(String fileName) { 
     int numOfComplex = 0; 
     Complex[] complexArray; 
     try { 
      Scanner sc = new Scanner(new File(fileName)); 
      String firstLine = sc.nextLine(); 
      firstLine = firstLine.trim(); 
      numOfComplex = Integer.parseInt(firstLine); 
      complexArray = new Complex[numOfComplex]; 
      for (int i = 0; i < numOfComplex; i++) { 
       String nextLine = sc.nextLine(); 
       nextLine = nextLine.trim(); 
       complexArray[i] = parseComplex(nextLine); 
      } 
     } 
     catch(Exception e) { 
     } 
     return complexArray; 
    } //<<<=== scope of `complexArray` ends here 

Answer 3

内

Answer 4

从@hemanth

public static Complex[] parseFromFile(String fileName) { 
     int numOfComplex = 0; 
     Complex[] complexArray = new Complex[numOfComplex]; // Need to initialize the array 
     try { 
      Scanner sc = new Scanner(new File(fileName)); 
      String firstLine = sc.nextLine(); 
      firstLine = firstLine.trim(); 
      numOfComplex = Integer.parseInt(firstLine); 
      complexArray = new Complex[numOfComplex]; 
      for (int i = 0; i < numOfComplex; i++) { 
       String nextLine = sc.nextLine(); 
       nextLine = nextLine.trim(); 
       complexArray[i] = parseComplex(nextLine); 
       } 
      return complexArray; 
     } 
     catch(Exception e) { 
      System.out.println("Exception was thrown"); // try adding this to see if an exception is thrown. 
     } 
     return complexArray; 
    } //<<<=== scope of `complexArray` ends here 

你需要创建一个新的复杂阵列初始化complexArray对象在继续。这是你的问题。

我认为这可能有效。如果一切正常，应该输入try子句。如果不是，它将返回大小为0的复数阵列。我假设如果发生这种情况，文件有问题，这意味着您需要手动执行某些操作。