Compile error in java :cannot find symbol.

Question

I have this code that is taking a text file and turning it into a string and then separating parts of the string into different elements of an arraylist.

import java.util.Scanner;
import java.io.*;
import java.util.ArrayList;

public class Grocery{

    public Grocery(){

        File inFile = new File ("lists.txt");
        Scanner input = new Scanner (inFile);
        String grocery;
        {
             grocery = input.nextLine();
        }
    }

    public void makeSmallerLists(){
        String listLine;
        String line;
        ArrayList<String> smallList = new ArrayList<String>();
        while(input.hasNextLine()){
            line = input.nextLine;
            if(line.equals("<END>")){
                smallList.add(listLine);
            } else{
                listLine = listLine + "\n" + line;
            }
        }
    }
}

However when I try to compile this it gives me two errors:

javac Message.java Message.java:31: cannot find symbol symbol : variable input location: class Message while(input.hasNextLine()){ ^ Message.java:32: cannot find symbol symbol : variable input location: class Message line = input.nextLine; ^

How do I fix this? I really don't know what's wrong.

I fixed that and now my error says $ javac Message.java Message.java:34: cannot find symbol symbol : variable nextLine location: class java.util.Scanner line = input.nextLine; ^

           ^

Now what is wrong?

Solution 1

 Scanner input = new Scanner (inFile);

input is local to the constructor, you cannot access outside of it, and you are trying to access in makeSmallerLists() method. Make it as a instance member, So that it available through out the class other than static context.

public class Grocery{

  Scanner input;

and in constructor

public Grocery(){

            File inFile = new File ("lists.txt");
             input = new Scanner (inFile);

Solution 2

You have variable scope problem. You can't get access a field outside of scope. Declare Scanner as globally, outside of costructor.

 public class Grocery{
    Scanner input = null;// Declare Scanner here.

    public Grocery(){
        .....
        input=new Scanner (inFile);
    }

Also append method bracket ().

      public void makeSmallerLists(){
       ......
        while(input.hasNextLine()){
        line = input.nextLine();// Append () after method. 
       .....
      }

Solution 3

That is because the Scanner object input has been declared inside your constructor(local scope of the constructor) and thus its not visible in your makeSmallerLists(). You need to declare it as an instance variable so that it would be accessible in all the methods of the class.

public class Grocery {
    Scanner input; // declared here, as an instance variable
    public Grocery(){
        File inFile = new File ("lists.txt");
        input = new Scanner (inFile);  // initialized here
        ...
    }
    ...
    public void makeSmallerLists() {
        ...
        while(input.hasNextLine()) { // accessible everywhere within the class
        ...
    }
}

Solution 4

One solution is to have a class member of type Scanner:

private Scanner input;

And in the constructor, construct it:

public class Grocery { 
   private Scanner input;

   public Grocery() {
      ...
      ...
      input = new Scanner (inFile);
   }
   ...
}

Now input is not limited to the scope of the constructor, it'll be accessible through the whole class.

---

Consider this example:

public class Example {
    int n = 0;  //n known everywhere in the class

    if(n == 0) {
       int n1 = 1;
       if(n1 == 1) {
          int n2 = 2;
          //n1 is known here
       }
       //n2 is not known here
    } 
    //n1 is not known here
}

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