Question

所以我试图显示一个符号化项目列表，让用户选择一个要删除的项目。

我将信息写入txt文件。
我将文件的内容存储在一个数组中。
我打印出阵列。
用户输入（例如L101），它将被删除文件。

问题出在步骤（1）当且仅当文件不存在时，我希望写入文件。所以我先于while循环，它将使用

if(file.isFile() ==false).

然而，这似乎使输出空白，就好像读者无法读取文件并将其存储在数组中一样。为什么？ PS如果我没有输入if和else语句，输出就可以了，只是它再次写入文件，我不想发生这种情况，我想要显示除用户输入内容之外的所有内容。

请在这里与我裸露我几乎没有从java开始。所以我深深地为任何错误道歉。这是代码

public static void main (String args[]) throws IOException
{
    //Declaring the file
     File tempFile = new File("D:\\myTempFile.txt");
    //Declaring the writer
     BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
    int n=0;
    int L=1;
    //Writing to the file if it did not exist
    if(tempFile.isFile()==false) 
    {

    while(n<15 && L<3)
        {
        n++;
        writer.write("L"+L+"0"+n);
        writer.newLine();
        L++;
        writer.write("L"+L+"0"+n);
        writer.newLine();
        L++;
        writer.write("L"+L+"0"+n);
        writer.newLine();
        L=1;
        //}

    }
     writer.close(); 
     freeParkingSpaces();
    }
    //read the and store to array if the file exists
    else if(tempFile.isFile()==true)
    {
        freeParkingSpaces();
    }

}                

public static void freeParkingSpaces() throws IOException
   {
     File tempFile = new File("D:\\myTempFile.txt");
   //using try and catch to handle errors and print propriet message instead. 
    try{ 
        Scanner readSpaces; // declare scanner variable.
//reading from file that contains the available spaces and storing them into an array.
System.out.println("Please choose one of the following parking spaces: ");
System.out.println(" ");
String [] freeSpaces= new String[45]; // declaring the array.
int i=0;

//getting input from file that contains the available spaces and storing them into an    array.
readSpaces=new Scanner(new File("D://myTempFile.txt")); 
System.out.print("\t\t");

//Display the values of the array which are the available spaces.
while(i<15 && readSpaces.hasNext()){
freeSpaces[i]=readSpaces.nextLine();
System.out.print("   "+freeSpaces[i]);
i++;
}
System.out.println(" ");
System.out.print("\t\t");
while(i>=15&&i<30&&readSpaces.hasNext()){
freeSpaces[i]=readSpaces.nextLine();
System.out.print("   "+freeSpaces[i]);
i++;
}
System.out.println(" ");
System.out.print("\t\t");
while(i>=30&&i<45&&readSpaces.hasNext()){
freeSpaces[i]=readSpaces.nextLine();

System.out.print("   "+freeSpaces[i]);
i++;
}
System.out.println(" ");
readSpaces.close();

//create scanner object to hold the input of a user which is a park space.
Scanner holder5=new Scanner(System.in); 
System.out.print("Your choice:  ");
String spaceName=holder5.nextLine();

//declaring files

File inputFile=new File("D://Temporary.txt");

// creating object to read from Free_ParkingSpaces file
BufferedReader reader=new BufferedReader(new FileReader(tempFile));
// creating object to write to the tempFile
BufferedWriter writer0=new BufferedWriter(new FileWriter(inputFile));
String currentLine;

while((currentLine = reader.readLine()) != null){
String trimmedLine = currentLine.trim();  
if(trimmedLine.equals(spaceName)) continue;//leave the required space by the user.
writer0.write(currentLine);   //write the lines to the tempFile.
writer0.newLine();   // start from new line.
}

writer0.close(); //close BufferedWriter Object

reader.close(); //close BufferedReader Object
tempFile.delete();  // Delete the old available spaces file.
inputFile.renameTo(tempFile); // Naming the temp file myTempFile.

System.out.println("Registration has completed successfuly");}


                                    catch(Exception e){
                        System.out.println("\n\t\t\t\tSorry, there's something     wrong try again!");}
                   }
}

Answer 1

isFile()检查它是否是文件（不是目录）

exists()检查文件是否存在。

http://docs.oracle.com/javase/7/docs/api/java/io/File.html

改变它。此外，在使用之前，请务必阅读有关该方法的文档并确切了解其用途。

注意，如果语句采用布尔值，那么if(file.exists()){}或if(file.isFile()){}是正确的方法

修改

由于您仍然无法将数据存入此文件，因此您应该这样做。

首先，处理IOException。当你执行throws IOException时，你基本上是说你将在更高级别处理异常，但是main也声明了这一点，因此异常永远不会被捕获（使用IDE和自动学习时出现的问题之一）校正）。

要实现这一目标，您需要这样做：

1）删除所有throws IOException

2）将捕获更改为

try{ //... } catch(IOException ioe){ ioe.printStackTrace(); } catch(Exception e){ System.out.println("\n\t\t\t\tSorry, there's something wrong try again!"); System.out.println("\n\t\t\t\tReason:"+e.getMessage()); }

执行此操作将显示是否存在任何IO异常。

您还可以评论tempFile.delete();以检查文件是否确实包含任何数据。如果你想一直删除它，那么创建一个新的

public static void main (String args[]) { //Declaring the file File tempFile = new File("D:\\myTempFile.txt"); if(!tempFile.exists()){ tempFile.createNewFile(); }

修改2

这是一个工作示例

public static void main(String[] args){ try{ File tempFile = new File("c:/testing/temp.txt"); tempFile.getParentFile().mkdirs(); tempFile.createNewFile(); writeToFile(tempFile); //readFromFile(); //deleteFile(); } catch(IOException ioe){ ioe.printStackTrace(); } } public static void writeToFile (File file) throws IOException{ //Declaring the writer BufferedWriter writer = new BufferedWriter(new FileWriter(file)); int n=0; int L=1; //Writing to the file if it did not exist while(n<15 && L<3) { n++; writer.write("L"+L+"0"+n); writer.newLine(); L++; writer.write("L"+L+"0"+n); writer.newLine(); L++; writer.write("L"+L+"0"+n); writer.newLine(); L=1; } writer.close(); }

if语句使输出空白

1 个答案: