Java programming help?

Question

There are several things I can not get my code to do. First I need it to read an external file which contains numbers and put it into an array. Next I need it to count how many numbers are in the file. Next, I cant get my main method to call the mode. I'm sure there may be other mistakes in my code, so any help will be greatly appreciated.

import java.util.*;
import java.io.*;

public class statisticsTest {
public static void main(String[] args)
throws FileNotFoundException {

double [] array;
double median;
double max;
double min;
double mean;
double mode;
double sd;

Scanner console = new Scanner(System.in);
System.out.print("File name: ");
String name = console.nextLine();
Scanner input = new Scanner(new File(name));

int arraysize=input.nextInt();
array = new double [arraysize];

System.out.println("There are " + arraysize + " numbers in your input file.");

max=max(array);
System.out.println("Max: "+ max);

min=min(array);
System.out.println("Min: "+ min);

mean=mean(array);
System.out.println("Mean: "+ mean);

median=median(array);
System.out.println("Median: "+ median);

System.out.println("Mode: ");

System.out.println("Standard Deviation: " + sd( array ) );

}

public static double median(double[] array){
int size = array.length;
double temp;
for (int i=0; i<size; i++){
for (int j=0; j<size-i-1; j++){
if(array[j]>array[j+1]){
temp = array[j];
array[j] = array[j+1];
array[j+1]=temp;
}
}
}

double med;
if ((size % 2) == 0){
med = (array[size / 2] + array[size / 2 - 1]) / 2.000;
} else {
med = array[size / 2];
}
return med;
}

public static double max(double[] array){
double max = array[0];
for (int j = 1; j < array.length; j++){
if (array[j] > max) {
max = array[j];
}
}
return max;
}

public static double min(double[] array){
double min = array[0];
for (int j = 1; j < array.length; j++){
if (array[j] < min){
min = array[j];
}
}
return min;
}

public static double mean(double[] array){
double mean = array[0];
for (int i=0; i<array.length; i++){
mean = mean + array[i];
}
return mean / array.length - 1;
}

public static double sd ( double[] array ){
double mean = 0;
double n = array.length;
if ( n < 2 ){
return Double.NaN;
}
for ( int i=0; i<n; i++ ){
mean += array[i];
}
mean /= n;
double sum = 0;
for ( int i=0; i<n; i++ ){
final double v = array[i] - mean;
sum += v * v;
}
return Math.sqrt( sum / ( n - 1 ) );
}

public static int mode(int [] array) {
int[] tally = new int[array.length];
for(int i = 0; i < tally.length; i++) {
tally[i] = 0;
}
for(int i = 0; i < array.length; i++) {
int value = array[i];
tally[value]++;
}
int maxIndex = 0;
for(int i = 1; i < tally.length; i++) {
if(tally[i] > tally[maxIndex]) {
maxIndex = i;
}
}
return maxIndex;
}
}

? · Accepted Answer

your mean function is wrong
because you are adding array[0]element two times
do like this
for(i=1;i<array.length;i++)
start the loop from 1st element
to store in array do like this
i do not know scanner but i think this will work
int n,size=0;
while((n=input.nextInt)!=null)
size++;
create a new scanner file object
Scanner sc=new Scanner(new File(name));
int i=0;
while((n=sc.nextInt)!=null)
{
array[i]=n;
i++;
}

modulo_function · Answer

It looks to me like you're just reading 1 int, using it to size that array, but you're not reading any more of the file!

I think that you need a loop to read from the file until you reach the end. Since you don't know (generally) how bit the file is, you should use an array list rather than an array:

ArrayList<Integer> value = new ArrayList<Integer>();

while( input.hasNext() ) {
...value.add(intput.nextInt();
}

Now you can rewrite your methods to take an array list OR size an array:
int[] array = new int[value.size()];
for( int k=0; k<value.size(); k++ ) array[k] = value.get(k);

Now you have an array with all the values. I recommend that you add some diagnostic prints to print each value as it's read from the file.

Java programming help?

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