Method declaration in java - return

Question

I have a question regarding this code, you can see in some methods that there are comments with a return, that is because I think I have to use a return method instead of a void method. My teacher told me to transform them to a void class, but isn't a method which modifies field variables suposed to return something? I'm in doubt because sometimes my teacher seems to not know so much about programming or has some doubts so, thank for your help beforehand.
public class ArraysClass {
private int[] array;
private int arrayLength;
public ArraysClass() {
setArrayLength();
array = new int[arrayLength];
}
public int setArrayLength() {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter a number to set the length of the array:");
arrayLength = scanner.nextInt();
System.out.println();
return arrayLength;
}
public void fillArray() {
Scanner scanner = new Scanner(System.in);
for (int i = 0; i < arrayLength; i++) {
System.out.println("Type a number to fill position " + i);
array[i] = scanner.nextInt();
}
// return array;
System.out.println();
}
public void findNumber() {
Scanner scanner = new Scanner(System.in);
int tofind, position;
System.out.println("Enter a number to search it in the array:");
tofind = scanner.nextInt();
position = Arrays.binarySearch(array, tofind);
if (position < 0) {
System.out.println("We did not find your number.");
} else {
System.out.println("The number you typed is in the next position: " + position);
}
System.out.println();
}
public void fillMethod() {
Scanner scanner = new Scanner(System.in);
int tofill;
System.out.println("Enter a number to fill the entire array with:");
tofill = scanner.nextInt();
Arrays.fill(array, tofill);
System.out.println();
//return array;
}
public void Sortmethod() {
Arrays.sort(array);
//return array;
}
private void showArray() {
System.out.println("Showing the array...");
for (int i = 0; i < arrayLength; i++) {
System.out.println(array[i]);
}
System.out.println();
}
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
ArraysClass arrayobj = new ArraysClass();
int choose;
do {
do {
System.out.println("1-Fill the array");
System.out.println("2-Find a number in the array");
System.out.println("3-Fill the entire array with a number");
System.out.println("4-Sort the array");
System.out.println("5-Show the array");
System.out.println("6-Exit");
System.out.println("Which one do you want to use?:");
choose = scanner.nextInt();
} while (choose < 1 && choose > 6);
switch (choose) {
case 1:
arrayobj.fillArray();
break;
case 2:
arrayobj.findNumber();
break;
case 3:
arrayobj.fillMethod();
break;
case 4:
arrayobj.Sortmethod();
break;
case 5:
arrayobj.showArray();
break;
case 6:
break;
}
} while (choose != 6);
}
}

Answer 1

In general, a method should return something if you need value from it. It is an approach used by some programmers to return a boolean even for do-only methods for success or failure or an int, for a status code. I do not follow these approaches. When I implement a method, I always ask myself how would I like to use that method. If I need a value from it, then it will have its type. Otherwise, it will be void. Let us see your methods:
setArrayLength: In general, from this name I would expect that you pass an int to it, representing the length and the method to be void. This is very common for setters, but here you are reading the actual value inside the method which is clearly inferior compared to having an int parameter, as your method will be useless if one wants to set the array length using a value not read from the console.
fillArray: I would expect this to be void, so I agree with its declaration, but again, the reading part should not be here.
findNumber: Should get the number to be found as a parameter and return an int, which represents its index, -1 if not found.
fillMethod: Should be void and should have an int parameter, which represents the value to be used to fill the array.
sortMethod: ok, maybe return the resulting array, but depends on your needs.
showArray: I would expect a PrintStream there, you will not necessarily output to System.out
General mistake: You mix methods with in/out operations to the console, the code is not general enough this way.