变量没有在java中定义try catch return语句

Question

显示未声明temp_lib，但已经声明了它。

库temp_lib已在try和return之后声明，temp_lib最后被写入，但它也要求我初始化变量。

int numAdded=0;
File inputfile;

inputfile = new File("export_Library.txt");
try {
    Library temp_lib;
    Scanner inputScanner = new Scanner(inputfile);
    System.out.println("processing a library...");
    String name=inputScanner.nextLine();
    int capacity=Integer.parseInt(inputScanner.next());
    temp_lib=new Library(name,capacity);

    LibraryItem item=new LibraryItem();
    while(inputScanner.hasNextLine()){
        item.setTitle(inputScanner.nextLine());
        item.setID_code(inputScanner.nextLine());
        item.setYearOfPublication(Integer.parseInt(inputScanner.nextLine()));
        if(inputScanner.next()=="1")
        {
            item.setOnLoan(true);
        }
        else
        {
            item.setOnLoan(false);
        }
        item.setReplacementCost(inputScanner.nextDouble());
    }   
    inputScanner.close();  
}
catch (IOException e) {
    System.out.println("IO Exception reading shapes from file"+e);
    e.printStackTrace() ;
    //return temp_lib;  
}
return temp_lib;

Answer 1

Library temp_lib;必须在try-catch块之前才能在try-catch块之后进入范围。

Library temp_lib = null; // you must give it an initial value, or the code
                         // won't compile 
try {
   ...
}
catch (..) {
   ...
}
return temp_lib;