java - 流对象初始化

Question

现在我在第 30 和 38 行收到编译时错误，表明 'fin' 可能尚未初始化。但这样写是完美的

 import java.io.*;
    class CopyFile {
        public static void main(String args[]) throws IOException {
            int i;
            FileInputStream fin;//can't it be done like this?
            FileOutputStream fout= new FileOutputStream(args[1]);

            try{
                //open input file
                try{
                    fin = new FileInputStream(args[0]);
                }
                catch(FileNotFoundException e){
                    System.out.println("Input file Not Found");
                    return;
                }
                //open output file
                try{
                    fout = new FileOutputStream(args[1]);
                }
                catch(FileNotFoundException e){
                    System.out.println("Error Opening File");
                }
            }
            catch(ArrayIndexOutOfBoundsException e){
                System.out.println("usage: Copyfile From to");
            }
            try{
                do{
                    i = fin.read();
                    if(i!= -1)
                        fout.write(i);
                }while(i != -1);
            }
            catch(IOException e){
                System.out.println("file error");
            }
            fin.close();
            fout.close();
        }
    }

我见过很多次这样初始化。我认为这是由于 try 块。

由于在 try 块中，它可能会错过初始化并因此出现错误？

Answer 1

问题是您没有初始化 FileInputStream fin根本。你的代码在编译器看来是这样的:

FileInputStream fin;
try {
    fin = ...
    //more code goes here...
} catch (...) {
    //exception handling...
} finally {
    fin.close(); //fin is not even null for the compiler
}

为了使代码工作，至少用 null 初始化它。值并检查是否 fin != null使用前 close方法。

FileInputStream fin = null;
try {
    fin = ...
    //more code goes here...
} catch (...) {
    //exception handling...
} finally {
    if (fin != null) {
        fin.close(); //fin is not null, at least the JVM could close it
    }
}

更多信息:

Java: Declaring Variables

Uninitialized variables and members in Java