为什么我的扫描仪无法读取文件？

Question

I'm trying to get my program to read data from a text file and store it in an array. The text file contains data about a planet. Here is an example:

Mercury
4.151002e10
2.642029e10
-1.714167e9
-3.518882e4
4.355473e4
6.785804e3
3.302e23

My file is named test.txt. It lives in the same directory as my class.java file. I've used System.out.println(new File("test.txt").getAbsolutePath()); to check if the directory path is correct, which it was, and I used System.out.println(new File(".")); to check if it was in the same directory that the code was trying to compile in, which again it was (outputted just a dot which I was led to believe meant it was in the correct directory). I've tried different ways of finding the file, such as renaming it to something else to check it wasn't a keyword, changing the encoding of the file to Unicode, or UTF-8, or ANSI, none of which worked, using .\\test in the file to look in the same directory, none of which worked.

Here is my code:

public static void defaultPlanetArray(){
  Planet[] solarSystem;
  solarSystem = new Planet[9];
  PhysicsVector dummyAcceleration = new PhysicsVector();

  System.out.println(new File("test.txt").getAbsolutePath());
  System.out.println(new File("."));

  try{
    File file = new File("C:\\Users\\Lizi\\Documents\\Uni Work\\Year 2\\PHYS281\\Project\\test.txt");
    Scanner scnr = new Scanner(file);
  }
  catch(FileNotFoundException e){
    System.out.println("File not found!");
  }
  int i = 0;

  while(i<9 && scnr.hasNextLine()){
    //read values from file and set as Planet object, then set to array.
    i++
  }

PhysicsVector and Planet are both classes I have created. PhysicsVector and the rest of Planet apart from this excerpt compile with no problems. When I try to compile this specific bit of code, I get:

.\\Planet.java:65: error: cannot find symbol while(i<9 && scnr.hasNextLine()){ ^

I'm guessing this means that the variable scnr is not being created in the try section because it cannot find the file. I think this because when I don't include the try and catch blocks, I get:

.\\Planet.java:59: error: unreported exception FileNotFoundException; must be caught or declared to be thrown Scanner scnr = new Scanner(file); ^

I've also tried the catches FileNotFoundException when I'm first creating the method but that gives me the same error as immediately above.

I could just set the values in the program, but that would give a lot of unnecessary code and be rather inefficient I think.

So my question is, how do I get the scanner to read my values from the file?

Answer 1

As @Lalit Verma pointed the scnr variable you defined lives inside the try - catch block.

Change the code to:

try{
    File file = new File("C:\\Users\\Lizi\\Documents\\Uni Work\\Year 2\\PHYS281\\Project\\test.txt");
    Scanner scnr = new Scanner(file);
    int i = 0;

    while(i<9 && scnr.hasNextLine()){
      //read values from file and set as Planet object, then set to array.
      i++
    }
  }catch(FileNotFoundException e){
    System.out.println("File not found!");
  }