使用参数化的类使用Java返回从指定文件读取的数据

Question

What I'm trying to do: During my tests, I have to read data from different files. (ID of user, ID of Office and so on. each id in separate file) The Idea to use class read_file(file_name); where file name – it would be name of file, where to read. What I have:

    public class Read_File {
    public static String client_number;
    private FileReader fr;

public static String read(String file_name){
String fileName=System.getProperty("user.dir")+"/src/resources/data_files/"+file_name+".txt";
try{
    FileReader inputFile = new FileReader(fileName);
    BufferedReader bufferReader = new BufferedReader(inputFile);

   String client_number = bufferReader.readLine();
    System.out.print("client number "+client_number);
   bufferReader.close();


} catch (FileNotFoundException e) {
    e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
} catch (IOException e) {
    e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
}
    return client_number;
}
public Read_File (FileReader fr) {
    this.fr = fr;

}
}

I'm trying to run it

  public void Find_Customer() {
    String client_number;

   Read_File file = new Read_File(fr);
   client_number = file.read("last_customer");
   System.out.print("client number"+client_number);
}

I'm able to read value from file but when I'm trying to get this value from method - I have null. I'm doning something completely wrong. could you help me to write it correct, please.

Answer 1

your method is static. you have 2 entities called client_number. One is a static member of the Read_File class and one is String client_number = bufferReader.readLine(); .

The scope of the local variable ends when the try block ends. You actually read that value but your return the value of the member client_number which is null.

Try this client_number = bufferReader.readLine(); (remove String type in front of this declaration). Also be careful that in case of an exception to return null.

Another solution is to remove the class member client_number (code would look like this):

public class Read_File {
private FileReader fr;

public static String read(String file_name){
String fileName=System.getProperty("user.dir")+"/src/resources/data_files/"+file_name+".txt";
String client_number = null;
try{
    FileReader inputFile = new FileReader(fileName);
    BufferedReader bufferReader = new BufferedReader(inputFile);

   client_number = bufferReader.readLine();
   System.out.print("client number "+client_number);
   bufferReader.close();


} catch (FileNotFoundException e) {
    e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
} catch (IOException e) {
    e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
}
    return client_number;
}
public Read_File (FileReader fr) {
    this.fr = fr;

}
}

As a side note, given that the method read is static you do not need to create an object of type Read_File .

Answer 2

Well, your mixing up several concepts of the java language... A quick and dirty fix would look like this:

public class Read_File {

    public static String read(String file_name){
        String client_number = "";
        String fileName=System.getProperty("user.dir")+"/src/resources" + 
            "/data_files"+file_name+".txt";
        try{
            FileReader inputFile = new FileReader(fileName);
            BufferedReader bufferReader = new BufferedReader(inputFile);

            String client_number = bufferReader.readLine();
            System.out.print("client number "+client_number);
            bufferReader.close();


        } catch (FileNotFoundException e) {
            e.printStackTrace();  
            //To change body of catch statement use File | Settings | File Templates.
        } catch (IOException e) {
            e.printStackTrace();  
            //To change body of catch statement use File | Settings | File Templates.
        }
        return client_number;
    }
}

Then you simply call it like that:

String client_number = Read_File.read("last_customer");