Question

Java quick sort, reading from a user input file into any array (to be sorted)

Asked by: elliottbenzle

Hey, What's up y'all,

I am trying to write some code in Java that will read in the numbers from a file (one # on each line of .txt file name inputted by user) put them into an array, and then run quick sort on the array. Eclipse is showing some red that I am having trouble with. My errors are marked with comments, and what the error is, if anyone can help me get this to run, thanks everyone!

-Kyle

import java.io.*;
import java.util.Scanner;
import java.io.BufferedReader;
import java.io.File; 

public class Lab3 { 
public static void main(String[] args) throws IOException{ 

System.out.print("Name of file with array: ");
Scanner readIn = new Scanner(System.in);
String input=readIn.nextLine();}
**testScan1(input);**  /*Eclipse says "return type for method is missing" trying to call method testScan below*/ 

**public testScan1(String filename)**  //"Return type is missing for method" 
{
File file = new File(filename);
Scanner scan;
try{
 int [] array = new int[5]; 
scan = new Scanner( file );
}
catch ( java.io.FileNotFoundException e )
{
System.out.println( "couldn't open. file not found "  );
return;
}
while(file.hasNext())      //"underlies "hasNext" "Method hasNext() is undefined"
{
for( int i = 0; i <= file.length(); ++i)
{ 
**array**[i]=scan.next();    //"Array cannot be Resolved" 

}
} 
int partition(int arr[], int left, int right)
{
 int i=left; int j = right;
 int tmp;
 int pivot = arr[(left+right)/2];
 while (i<=j){
  while(arr[i]<pivot)
   i++;
  while (arr[j]>pivot)
   j--;
  if (i<=j){
   tmp=arr[i];
   arr[i]=arr[j];
   arr[j]=tmp;
   i++; j--;
  }
 }
 return i;
    }
    void quickSort(int arr[], int left, int right){
 int index = partition(arr, left, right);
 if (left<index-1);
 quickSort(arr, left, index-1);
 if (index<right)
  quickSort(arr, index, right);
    }
    }
                                  
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Asked On
2009-11-05 at 14:56:16ID24876426
Tags

Java

,

quicksort

,

filereader

,

array

Topics

Eclipse

,

Java Programming Language

,

New to Java Programming

Participating Experts
1
Points
250
Comments
3

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Answers

 

by: CEHJPosted on 2009-11-05 at 15:05:05ID: 25755084

You need to get your braces and methods right. This compiles:

import java.io.*;
import java.io.BufferedReader;
import java.io.File; 
import java.util.Scanner; 

public class Lab3 {
    public static void main(String[] args) throws IOException {
        System.out.print("Name of file with array: "); 
        Scanner readIn = new Scanner(System.in);
        String input = readIn.nextLine();
    } 
    public static void testScan1(String filename) //"Return type is missing for method" 
     {
        File file = new File(filename);
        Scanner scan; 
        try {
            int[] array = new int[5];
            scan = new Scanner(file);
        } catch (java.io.FileNotFoundException e) {
            System.out.println("couldn't open. file not found "); 
            return;
        } 
        while (scan.hasNext()) //"underlies "hasNext" "Method hasNext() is undefined"
         {
            for (int i = 0; i <= file.length(); ++i) {
                //    **array**[i]=scan.next();    //"Array cannot be Resolved" 
            }
        }
    } 
    int partition(int[] arr, int left, int right) {
        int i = left;
        int j = right;
        int tmp;
        int pivot = arr[(left + right) / 2]; 
        while (i <= j) {
            while (arr[i] < pivot)
                i++; 
            while (arr[j] > pivot)
                j--; 
            if (i <= j) {
                tmp = arr[i];
                arr[i] = arr[j];
                arr[j] = tmp;
                i++;
                j--;
            }
        } 
        return i;
    } 
    void quickSort(int[] arr, int left, int right) {
        int index = partition(arr, left, right); 
        if (left < (index - 1)) {
            ;
        } 
        quickSort(arr, left, index - 1); 
        if (index < right) {
            quickSort(arr, index, right);
        }
    }
}
                                              
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by: CEHJPosted on 2009-11-05 at 15:10:02ID: 25755120

This will fix your array problem

	while (scan.hasNext()) 
	{
	    for (int i = 0; i <= file.length(); ++i) {
		array[i]=scan.nextInt();
	    }
	}
                                              
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by: CEHJPosted on 2009-11-06 at 03:06:19ID: 25758118

:-)

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