Change from ArrayList to Array of Strings Java

Question

I have this java method which returns an ArrayList, but I want to return an Array of Strings. The method reads the file words.txt (contains all words with a word on each line), and I want to store those words into an Array of Strings.

Heres the code I already have:

public static ArrayList<String> readFile(){
    File myFile=new File("./src/folder/words.txt");
    Scanner s1=null;

    //Creates ArrayList to store each String aux
    ArrayList<String> myWords = new ArrayList<String>();

    try {
        s1 = new Scanner(myFile);
    }catch (FileNotFoundException e) {

        System.out.println("File not found");
        e.printStackTrace();
    }
    while(s1.hasNext()){
        String aux=s1.next();
        System.out.println(aux);

    }
    s1.close();
    return myWords;
}

Can I change this code to return a String []?

https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#toArray-T:A- — Amir Afghani, Mar 15 '18 at 03:03
*"Can I change this code to return a String []?"* - Yes, but. You will need to know the number lines you are going to before you can declare the array. Alternately, you could read the content into the `ArrayList` and then use this to create a new array of `String`s (as you will know how many elements you need). On a side note. You should not be referencing `src` at all, it won't exist once the program is compiled and exported. You should also not be reading from `s1` if there was an error, this will create a `NullPointerException` — MadProgrammer, Mar 15 '18 at 03:04
see this [question](https://stackoverflow.com/questions/2745338/convert-an-arraylist-to-an-object-array) , that's the same — focus mind, Mar 15 '18 at 03:05
I know the number of lines, so I think I can do it! Should I do create the object String array? With the size and that stuff? Or how are you suggesting? Can you do code please? It might help a lot. — Pedro, Mar 15 '18 at 03:10

score 2 · Answer 1 · answered Mar 15 '18 at 03:05

You can call List.toArray(String[]) to convert the List<String> to a String[]. I would also prefer a try-with-resources over explicitly closing the Scanner and a List<String> interface. Something like,

public static String[] readFile() { // <-- You could pass File myFile here
    File myFile = new File("./src/folder/words.txt");

    // Creates ArrayList to store each String aux
    List<String> myWords = new ArrayList<>();

    try (Scanner s1 = new Scanner(myFile)) {
        while (s1.hasNext()) {
            String aux = s1.next();
            System.out.println(aux);
        }
    } catch (FileNotFoundException e) {
        System.out.println("File not found");
        e.printStackTrace();
    }
    return myWords.toArray(new String[0]);
}

I'm importing this: import java.awt.List; but there's an error in the line 5 "List" — Pedro, Mar 15 '18 at 03:08
@Pedro `import java.util.List;` - Please click on the JavaDoc link **in** my answer. — Elliott Frisch, Mar 15 '18 at 03:18

Manuj · Answer 2 · 2020-10-02T04:03:37.310

try using a built in function of collections class .

    ArrayList<String> stringList = new ArrayList<String>();
    stringList.add("x");
    stringList.add("y");
    stringList.add("z");
    stringList.add("a");

    /*ArrayList to Array Conversion */
    /*You can use the toArray method of the collections class and pass the  new String array object in the constructor while making a new String array*/
    String stringArray[]=stringList.toArray(new String[stringList.size()]);

    
    for(String k: stringArray)
    {
        System.out.println(k);
    }

Shahid · Answer 3 · 2018-03-15T03:18:59.280

1

Add this at last:

String [] arr = myWords.toArray(new String[myWords.size()]);
return arr;

Or simply,

return myWords.toArray(new String[myWords.size()]);

edited Mar 15 '18 at 03:18

answered Mar 15 '18 at 03:06

Shahid

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Change from ArrayList to Array of Strings Java

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