Printing Int Array to File using PrintWriter

[Jim Hester]

I'm hoping this is a simple fix and I'm just overlooking something. In the PrintArray method, I really want to send that output to the file, but pw.print won't work. Does the method not inherit or know that I've already initialized the PrintWriter?? What's a way to fix this other than hardcoding it in?

  package reversearray;

import java.io.*;

public class ReverseArray {

    public static void Reverse(int[] array, int n){
        int left = 0;        // Index of left most point in array
        int right = n - 1;   // Index of right most point in array

        // Logic to swap the elements of the array
        while (left < right){
            int temp = array[left];
            array[left] = array[right];
            array[right] = temp;
            left++;     // increment the pointer
            right--;    // decrement the point
        }
    }

    public static void PrintArray(int[] a) throws IOException{

        // Just want to print out the array so it's readable.
        for (int i = 0; i < a.length ; i++){
            System.out.print(a[i]);
            System.out.print(", ");
        }
        System.out.println();
    }

    public static void main (String [] args) throws IOException{
        int[] first = {1};
        int[] second = {1,5};
        int[] third = {1, 5, 8};
        int[] fourth = {5, 20, 89, 54, 72, 93, 99, 102, 43};
        int[] fifth = {43, 102, 99, 93, 72, 54, 89, 20, 5, 70, 32, 1};
        
        File file = new File("arrays.txt");
        PrintWriter pw = new PrintWriter(file);
        
        pw.println("Starting the reverse program");
        pw.println();
        
        // First Array
        pw.println("Testing the first array");
        pw.println("The initial elements of the first array are: ");
        PrintArray(first);
        Reverse(first, first.length);
        pw.println("The elements after reversing: ");
        PrintArray(first);
        pw.println();
        
        // Second Array
        pw.println("Testing the second array");
        pw.println("The initial elements of the second array are: ");
        PrintArray(second);
        Reverse(second, second.length);
        pw.println("The elements after reversing: ");
        PrintArray(second);
        pw.println();
        
        // Third Array
        pw.println("Testing the third array");
        pw.println("The initial elements of the third array are: ");
        PrintArray(third);
        Reverse(third, third.length);
        pw.println("The elements after reversing: ");
        PrintArray(third);
        pw.println();
        
        // Fourth Array
        pw.println("Testing the fourth array");
        pw.println("The initial elements of the fourth array are: ");
        PrintArray(fourth);
        Reverse(fourth, fourth.length);
        pw.println("The elements after reversing: ");
        PrintArray(fourth);
        pw.println();
        
        // Fifth Array
        pw.println("Testing the fifth array");
        pw.println("The initial elements of the fifth array are: ");
        PrintArray(fifth);
        Reverse(fifth, fifth.length);
        pw.println("The elements after reversing: ");
        PrintArray(fifth);
        pw.println();

        // Close the File
        pw.close();
    }
}  

[Campbell Ritchie]

Why don't you use a Formatter if you are writing plain text to a file? It's easier to use than a PrintWriter?
Anyway, wouldn't you use a BufferedWriter wrapped round a FileWriter?
Why are you starting the names of your methods with Capital Letters?

[Sebastian Janisch]

how about ...

pw.print(printArray(array));

One thing... the Java Code Convention defines that class names and constructors start with a capital letter, methods don't. ;-)

[Campbell Ritchie]

That looks pretty disastrous, I am afraid.

Just from memory, so you will have to check the details in the API or the Java™ Tutorials

try
{
  BufferedWriter bw = null;
  try
  {
    bw = new BufferedWriter(new FileWriter(myFile));
    for (int i : numbers)
    {
      bw.writeInt(i);
      bw.write(" ");
    }
    bw.writeLine();
  }
  finally
  {
    if (bw != null)
      bw.close();
  }
}
catch (FileNotFoundException fnf)
{
 . . .
}
catch (IOException ioe)
{
 . . .
}

I am pretty sure I have got most of the method names wrong, but you can check that in the API. You will notice that you can add "true" as a parameter to the FileWriter constructor; it tells you in the API what that means. A Formatter is still probably easier to use. You will also have to put something in the catch. And also work out why I have put two "try"s inside each other with a "finally".

[Sebastian Janisch]

Sebastian Janisch wrote:how about ...

pw.print(printArray(array));

One thing... the Java Code Convention defines that class names and constructors start with a capital letter, methods don't. ;-)

I forgot one thing..

either the print array method returns a string with whatever needs to be written to the file or you set the system out to your PrintWriter and leave the method the way it is ...

that would be

System.out = pw; 

printArray(five);

[Jim Hester]

Thanks much. I just modified the method so it returned a string, and went from there. I also fixed the naming conventions. Final code below. Thanks!!

 import java.io.*;

public class ReverseArray {

    public static void reverse(int[] array, int n){
        int left = 0;        // Index of left most point in array
        int right = n - 1;   // Index of right most point in array

        // Logic to swap the elements of the array
        while (left < right){
            int temp = array[left];
            array[left] = array[right];
            array[right] = temp;
            left++;     // increment the pointer
            right--;    // decrement the pointer
        }
    }

    public static String printArray(int[] a){
        String print = new String();
        // Just want to creat a string to print so it's readable.
        for (int i = 0; i < a.length ; i++){
            print = print + a[i] + ", ";
        }
        print = print + "\n";
        return print;
    }

    public static void main (String [] args) throws IOException{
        // The arrays to be reversed hard-coded in. 
        int[] first = {1};
        int[] second = {1,5};
        int[] third = {1, 5, 8};
        int[] fourth = {5, 20, 89, 54, 72, 93, 99, 102, 43};
        int[] fifth = {43, 102, 99, 93, 72, 54, 89, 20, 5, 70, 32, 1};
        
        // Open the file and create an object to pring
        File file = new File("arrays.txt");
        PrintWriter pw = new PrintWriter(file);
        
        pw.println("Starting the reverse program");
        pw.println();
        
        // First Array
        pw.println("Testing the first array");
        pw.println("The initial elements of the first array are: ");
        pw.println(printArray(first));
        reverse(first, first.length);
        pw.println("The elements after reversing: ");
        pw.println(printArray(first));
        pw.println();
        
        // Second Array
        pw.println("Testing the second array");
        pw.println("The initial elements of the second array are: ");
        pw.println(printArray(second));
        reverse(second, second.length);
        pw.println("The elements after reversing: ");
        pw.println(printArray(second));
        pw.println();
        
        // Third Array
        pw.println("Testing the third array");
        pw.println("The initial elements of the third array are: ");
        pw.println(printArray(third));
        reverse(third, third.length);
        pw.println("The elements after reversing: ");
        pw.println(printArray(third));
        pw.println();
        
        // Fourth Array
        pw.println("Testing the fourth array");
        pw.println("The initial elements of the fourth array are: ");
        pw.println(printArray(fourth));
        reverse(fourth, fourth.length);
        pw.println("The elements after reversing: ");
        pw.println(printArray(fourth));
        pw.println();
        
        // Fifth Array
        pw.println("Testing the fifth array");
        pw.println("The initial elements of the fifth array are: ");
        pw.println(printArray(fifth));
        reverse(fifth, fifth.length);
        pw.println("The elements after reversing: ");
        pw.println(printArray(fifth));
        pw.println();

        // Close the File
        pw.close();
    }
}   

[Evan Caballero]

You should re-write your printArray method like this, because String is immutable. A new String instance is created each time you call a method on it.
The use of StringBuffer is preferred ;)

    public static String printArray(int[] a){
        StringBuffer print = new StringBuffer();
        // Just want to creat a string to print so it's readable.
        for (int i = 0; i < a.length ; i++){
            print.append(a[i] + ", ");
        }
        print.append("\n");
        return print.toString();
    }

[Sebastian Janisch]

In your printArray method: use StringBuilder instead of String.

[Campbell Ritchie]

Agree with SJ. StringBuilder is usually better than StringBuffer.

[Evan Caballero]

Isn't StringBuffer a sub class of StringBuilder ?

[Campbell Ritchie]

No

[Sebastian Janisch]

stringbuilder vs stringbuffer

[Evan Caballero]

nice, thanks ;)

[Jim Hester]

Thanks! Wasn't aware of StringBuilder. Made the appropriate changes.