Why are my methods not returning anything?

I've written this code to do several calculations regarding arrays of characters, integers, and doubles.

static char minimum(char array[])
{   
char min = 'z';
int n = array.length;
for (int i = 0; i < n-1; i++)
{
if (array[i] < min)
{
min = array[i];
}
}
return min;
}
static int minimum(int array[])
{
Arrays.sort(array);  
return array[0];
}
static double minimum(double array[])
{
int n = array.length;
Arrays.sort(array);  
return array[0
];
}
static char maximum(char array[])
{
char max = 'z';
int n = array.length;
for (int i = 0; i < n-1; i++)
if (array[i] > max)
{
max = array[i];
}
return max;
}
static int maximum(int array[])
{
int n = array.length;
Arrays.sort(array);  
return array[n - 1];
}
static double maximum(double array[])
{
int n = array.length;
Arrays.sort(array);  
return array[n - 1];
}
static int minimumat(char array[])
{
char min = 'z';
int n = array.length;
int minat = 0;
for (int i = 0; i < n-1; i++)
{
if (array[i] < min)
{
min = array[i];
}
}
for (int i = 0; i < n; i++)
{
if (array[i] == min)
{
i = minat;
}
}
return minat;
}
static int minimumat(int array[])
{
int n = array.length;
int newarray[] = array;
Arrays.sort(newarray);  
int min = newarray[0];
int minat = 0;
for(int i = 0; i <= n; i++)
{
if(array[i] == min)
{
minat = i;
}
}
return minat;
}
static int minimumat(double array[])
{
int n = array.length;
double newarray[] = array;
Arrays.sort(newarray);  
double min = newarray[0];
int minat = 0;
for(int i = 0; i <= n; i++)
{
if(array[i] == min)
{
minat = i;
}
}
return minat;
}
static int maximumat(char array[])
{
char max = 'A';
int n = array.length;
int maxat = 0;
for (int i = 0; i < n; i++)
{
if (array[i] > max)
{
max = array[i];
}
}
for (int i = 0; i < n; i++)
{
if (array[i] == max)
{
i = maxat;
}
}
return maxat;
}
static int maximumat(int array[])
{
int n = array.length;
int newarray[] = array;
Arrays.sort(newarray);  
int max = newarray[0];
int maxat = 0;
for(int i = 0; i <= n; i++)
{
if(array[i] == max)
{
maxat = i;
}
}
return maxat;
}
static int maximumat(double array[])
{
int n = array.length;
double newarray[] = array;
Arrays.sort(newarray);  
double max = newarray[n - 1];
int maxat = 0;
for(int i = 0; i <= n; i++)
{
if(array[i] == max)
{
maxat = i;
}
}
return maxat;
}
static double average(int array[])
{
int sum = 0;
int n = array.length;
for (int i = 0; i < array.length; i++)
{
sum +=  array[i];
}
double avg = sum / n;
return avg;
}
static double average(double array[])
{
double sum = 0;
int n = array.length;
for (int i = 0; i < array.length; i++)
{
sum += array[i];
}
double avg = sum / n;
return avg;
}

I have also written some simple code to test these methods in another class.

public static void main(String[] args)
{
char[] charArray = {'k', 'p', 'f', 'r', 'D', 'm'};
double doubleArray[] = {5.43, 9.81, 5.37, 7.19, 2.86, 6.55, 2.37, 7.28};
int intArray[] = {40, 7, 53, 34, 61, 70, 29, 49};
ArrayTools ArrayTools = new ArrayTools();
System.out.println(ArrayTools.minimum(charArray));
System.out.println(ArrayTools.minimum(doubleArray));
System.out.println(ArrayTools.minimum(intArray));
System.out.println(ArrayTools.maximum(charArray));
System.out.println(ArrayTools.maximum(doubleArray));
System.out.println(ArrayTools.maximum(intArray));
System.out.println(ArrayTools.minimumat(charArray));
System.out.println(ArrayTools.minimumat(doubleArray));
System.out.println(ArrayTools.minimumat(intArray));
System.out.println(ArrayTools.maximumat(charArray));
System.out.println(ArrayTools.maximumat(doubleArray));
System.out.println(ArrayTools.maximumat(intArray));
System.out.println(ArrayTools.average(intArray));
System.out.println(ArrayTools.average(doubleArray));
}

}

The code has worked properly for the "minimum" and "maximum" methods (not to be confused with the "minimumat" and "maximumat" methods). But the rest haven't printed anything.

Here is the output:

D 
2.37 
7 
z 
9.81 
70

2 problems I see in your code is-

1 - In static int minimumat(char array[]) method you are resetting value of i. It should be

minat = i;

and similarly maxat in other method- maximumat()

2- You are looping from 0 to length (n), so you might get ArrayIndexOutOfBound on last index, so exclude the last one. It should be

for(int i = 0; i < n; i++) {