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how to create a min,max, and average methods in a generic class?(Java)

I have a problem in implementing those methods(min, max, and average ) in my generic class. I have already specified the return type as E but it seems hard to get it to work. if anyone has an example for implementing those methods I would really appreciate it.
public E ave() {
int total = 0;
for (int i = 0; i < size(); i++) {
total = (total + bag[i]);
}
int ave = (total / size());
return ave;
}
public int minimum() {
int min = bag[0];
for (int a = 1; a < size(); a++) {
if (bag[a] < min) {
min = bag[a];
}
}
return min;
}

First define some interface with int method that will be used by your math class.
public interface IntHolder {
int getIntValue();
}
Add contraint to generic E such that E extends IntHolder i. e. only IntHolder implementations can be added in GenericArrayMath. Since all objects are guarenteed to be of IntHolder type, now you can use in your math methods getIntValue() of given object.
Note, unconstrained E can by anything so it is impossible to predict by compiler object fields/methods. The only thing that you can be sure about E is, that it extends Object (as all classes extends Object by default), thus you can only use Object's methods.
public class GenericArrayMath<E extends IntHolder> {
private final E[] bag;
public GenericArrayMath(Class<E> clazz, int length) {
bag = (E[]) Array.newInstance(clazz, length)
}
public void set(int i, E e) { bag[i] = e; }
public int min() {
int min = Integer.MAX_VALUE;
for (int i = 0; i < bag.length; i++) {
if (bag[i] == null) { continue; } // skip
if (bag[i] < min) { min = bag[i]; }
}
return min;
}
public int max() {
int max = Integer.MIN_VALUE;
for (int i = 0; i < bag.length; i++) {
if (bag[i] == null) { continue; } // skip
if (bag[i] > max) { max = bag[i]; }
}
return max;
}
public double avg() {
double sum = 0;
int nonNullCount = 0;
for (int i = 0; i < bag.length; i++) {
if (bag[i] == null) { continue; } // skip
sum += bag[i].getIntValue();
nonNullCount++;
}
return sum / nonNullCount;
}
}
Example of IntHolder implementation:
public class Person extends IntHolder {
public final String name;
public final int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
#Override
public int getIntValue() { return age; }
}
and finally GenericArrayMath usage:
GenericArrayMath<Person> gam = new GenericArrayMath<>(Person.class, 3);
gam.set(0, new Person("a", 20));
gam.set(1, new Person("b", 30));
gam.set(2, new Person("c", 40));
int minAge = gam.min();
int maxAge = gam.max();
double avgAge = gam.avg();
Hope it helps.

I want to search a specific element of an array and if it exists to return its index

I have created an array of type Savings which contains a String (Name) and a double (Account Number). I want to search using an Account Number and see if it exist and then return all the elements (Name + Account Number) and the Index of the Array that contain these elements. I tried this but it does not work.
import java.util.Arrays;
import java.util.Scanner;
public class Main {
public static void main(String[] args){
Savings[] ArrayOfSavings = new Savings[5];
System.out.print("Enter Account Number: ");
Scanner scan = new Scanner(System.in);
double Ms = scan.nextDouble();
//Loop until the length of the array
for(int index = 0; index<= ArrayOfSavings.length;index++){
if(ArrayOfSavings[index].equals(Ms)){
//Print the index of the string on an array
System.out.println("Found on index "+index);
}
}
ArrayOfSavings[0] = new Savings("Giorgos",87654321);
ArrayOfSavings[1] = new Savings("Panos",33667850);
}
}
/Savings Class/
public class Savings extends Generic {
public Savings(String FN, double AN) {
super(FN, AN);
}
#Override
public String toString(){
return String.format("Customer: %s \n Acount Number: %.1f,
getFirstName(),getAccNumber();
}
}

You could do something like this, where you return -1 if it doesn't exist, or the index if you've found it. Just have to make sure you check for this case.
public static int findSavingsIfExists(double accountNumber, Savings[] allSavings) {
for(int i = 0; i < allSavings.length(); i++) {
if(allSavings[i].accountNumber == accountNumber) {
return i;
}
}
return -1;
}
and use it like so
int index = findSavingsIfExists(..., ArrayOfSavings);
if(index != -1) {
Savings foundSavings = ArrayOfSavings[index];
} else {
//Not found
}

Try to use somethig like this:
double Ms = scan.nextDouble();
int index = 0;
for (int i = 0; i < ArrayOfSavings.length; i++) {
if (ArrayOfSavings[i].getAccountNumber == Ms ) {
index = i;
break;
}
}
System.out.println(index);

Finding item with the lowest cost in an ArrayList

What I need to do is find the inventory item with the lowest cost from an array list. If there are none, return "N/A". So I can't really figure out how to find the smallest value out of all the inventory item costs. This is what I have so far. My plan was to set cost equal to the first inventory item and cycle through each item checking if it's cost is less but I'm confused on how to do that or if that is even the correct way of doing it.
EDIT: We have not covered for loops yet so I cannot use them. I can only use while loops
public InventoryItem itemWithLowestCost() {
if (inventoryList.size() > 0) {
int i = 0;
while (i < inventoryList.size()) {
double cost = inventoryList.get(i).getCost();
if (cost < )
}
}
else {
return "N/A";
}
}
Here is my InventoryItem constructor. I'm not sure if this is needed to understand the above code but here it is anyway
public InventoryItem(String descriptionIn, double costIn, double percentDepreciatedIn) {
description = descriptionIn.trim();
cost = costIn;
percentDepreciated = percentDepreciatedIn;
}

You can do it by checking the length to be non-zero, then picking the cost of element zero as "tentative best", and comparing it to costs of other elements on the list:
if (inventoryList.size() > 0) {
int best = 0;
int i = 1;
while (i < inventoryList.size()) {
double cost = inventoryList.get(i).getCost();
if (cost < inventoryList.get(best).getCost()) {
best = i;
}
i++;
}
return inventoryList.get(best);
} else {
return "N/A";
}

You can do it with a O(n) loop
public InventoryItem itemWithLowestCost() {
int size = (inventoryList == null || inventoryList.isEmpty()) ?
0 : inventoryList.size();
InventoryItem min = (size > 0) ? inventoryList.get(0) : null;
for (int i = 1; i < size; i++) {
InventoryItem ii = inventoryList.get(i);
if (ii.getCost() < min.getCost()) min = ii;
}
return min;
}
Note: That you can't return a String N/A as an InventoryItem instance (so this returns null).

You could use a comparitor to sort the inventory by cost, lowest to highets.
public InventoryItem itemWithLowestCost(Collection<InventoryItem> inventory) {
if(inventory != null && !inventory.isEmpty()) {
Collections.sort(inventory, new Comparator<InventoryItem>() {
#Override
public int compare(InventoryItem i1, InventoryItem i2) {
return i1.getCost() - i2.getCost();
}
});
return inventory.get(0);
}
return null;
}

How do i return 2 values from a single method

import java.util.Scanner;
public class fmax
{
public static void main(String[] args)
{
int max;
max = maxnum();
System.out.println("The max number is: " + max);
}
public static int maxnum()
{
int max = 0, element = 0;
Scanner keyboard = new Scanner(System.in);
int []fmax = new int[10];
for(int i = 0; i < fmax.length; i++)
{
System.out.print("Enter number " + (i+1) + ":");
fmax[i] = keyboard.nextInt();
if(fmax[i] > max)
{
max = fmax[i];
element = i; //the variable i want to be returned
}
}
return max;
}
}
Okay, I am able to return a max value in this program, however, I would like to return the value of the element/index assigned to the max value that I return. How would i go about doing that?

to return two values pack it into some object and return it ;)
public class ReturnedObject{
private Object val1;
private Object val2;
//getters setters
}
public ReturnedObject yourMethod(){
ReturnedObject returnedObject = new ReturnedObject();
returnedObject.setVal1("yourVal1");
returnedObject.setVal2("yourVal2");
return returnedObject;
}

You can pass the values into arrays/objects. (I am not saying that you can return an array).If you pass array into the method as one of the parameters, the values of the array shall remain. You can access the values from there.
Note: If you find yourself in need of returning more than one value using one method, you should consider re-designing your codes.

Algorithm course: Output of int sort and method to sort Strings

My assignment asks me to make a TV show program, where I can input shows, delete, modify and sort them. What I'm stuck on is the sorting part. With the show, it asks for the name, day a new episode premieres, and time. Those are the keys I need to sort it by.
The program prompts the user to input one of those keys, then the program needs to sort (sorting by day will sort alphabetically).
I made a class and used an array. Here is the class:
public class showInfo
{
String name;
String day;
int time;
}
And the method to sort by time in the code:
public static void intSort()
{
int min;
for (int i = 0; i < arr.length; i++)
{
// Assume first element is min
min = i;
for (int j = i+1; j < arr.length; j++)
{
if (arr[j].time < arr[min].time)
{
min = j;
}
}
if (min != i)
{
int temp = arr[i].time;
arr[i].time = arr[min].time;
arr[min].time = temp;
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < arr.length; i++)
{
System.out.println(arr[i].name + " - " + arr[i].day + " - " + arr[i].time + " hours");
}
}
When I call it and output it in the main, it only shows "TV Shows by Time" and not the list. Why is this?
Also, I need to make ONE method that I will be able to use to sort both the day AND the name (both Strings). How can I do this without using those specific arrays (arr[i].name, arr[i].day) in the method?
Any help would be greatly appreciated! Thanks in advance!

In this part of your code
if (min != i) {
int temp = arr[i].time;
arr[i].time = arr[min].time;
arr[min].time = temp;
}
You're just changing the time when you should move the whole object instead. To fix it, the code must behave like this:
if (min != i) {
//saving the object reference from arr[i] in a temp variable
showInfo temp = arr[i];
//swapping the elements
arr[i] = arr[min];
arr[min] = temp;
}
I̶t̶ ̶w̶o̶u̶l̶d̶ ̶b̶e̶ ̶b̶e̶t̶t̶e̶r̶ ̶t̶o̶ ̶u̶s̶e̶ ̶ Arrays#sort ̶w̶h̶e̶r̶e̶ ̶y̶o̶u̶ ̶p̶r̶o̶v̶i̶d̶e̶ ̶a̶ ̶c̶u̶s̶t̶o̶m̶ ̶̶C̶o̶m̶p̶a̶r̶a̶t̶o̶r̶̶ ̶o̶f̶ ̶t̶h̶e̶ ̶c̶l̶a̶s̶s̶ ̶b̶e̶i̶n̶g̶ ̶s̶o̶r̶t̶e̶d̶ ̶(̶i̶f̶ ̶y̶o̶u̶ ̶a̶r̶e̶ ̶a̶l̶l̶o̶w̶e̶d̶ ̶t̶o̶ ̶u̶s̶e̶ ̶t̶h̶i̶s̶ ̶a̶p̶p̶r̶o̶a̶c̶h̶)̶.̶ ̶S̶h̶o̶r̶t̶ ̶e̶x̶a̶m̶p̶l̶e̶:̶
showInfo[] showInfoArray = ...
//your array declared and filled with data
//sorting the array
Arrays.sort(showInfoArray, new Comparator<showInfo>() {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
//basic implementation
if (showInfo1.getTime() == showInfo2.getTime()) {
return showInfo1.getName().compareTo(showInfo2.getName());
}
return Integer.compare(showInfo1.getTime(), showInfo2.getTime());
}
});
//showInfoArray will be sorted...
Since you have to use a custom made sorting algorithm and support different ways to sort the data, then you just have to change the way you compare your data. This mean, in your current code, change this part
if (arr[j].time < arr[min].time) {
min = j;
}
To something more generic like
if (compare(arr[j], arr[min]) < 0) {
min = j;
}
Where you only need to change the implementation of the compare method by the one you need. Still, it will be too complex to create and maintain a method that can support different ways to compare the data. So the best option seems to be a Comparator<showInfo>, making your code look like this:
if (showInfoComparator.compare(arr[j], arr[min]) < 0) {
min = j;
}
where the showInfoComparator holds the logic to compare the elements. Now your intSort would become into something more generic:
public static void genericSort(Comparator<showInfo> showInfoComparator) {
//your current implementation with few modifications
//...
//using the comparator to find the minimum element
if (showInfoComparator.compare(arr[j], arr[min]) < 0) {
min = j;
}
//...
//swapping the elements directly in the array instead of swapping part of the data
if (min != i) {
int temp = arr[i].time;
arr[i].time = arr[min].time;
arr[min].time = temp;
}
//...
}
Now, you just have to write a set of Comparator<showInfo> implementations that supports your custom criteria. For example, here's one that compares showInfo instances using the time field:
public class ShowInfoTimeComparator implements Comparator<showInfo> {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
return Integer.compare(showInfo1.getTime(), showInfo2.getTime());
}
}
Another comparator that uses the name field:
public class ShowInfoNameComparator implements Comparator<showInfo> {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
return showInfo1.getName().compareTo(showInfo2.getName());
}
}
Now in your code you can call it like this1:
if (*compare by time*) {
genericSort(showInfoArray, new ShowInfoTimeComparator());
}
if (*compare by name*) {
genericSort(showInfoArray, new ShowInfoNameComparator());
}
if (*another custom rule*) {
genericSort(showInfoArray, new ShowInfoAnotherCustomRuleComparator());
}
where now you can implement a custom rule like compare showInfo objects using two or more fields. Taking as example your name and day fields (as stated in the question):
public class ShowInfoNameAndDayComparator implements Comparator<showInfo> {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
int nameComparisonResult = showInfo1.getName().compareTo(showInfo2.getName());
if (nameComparisonResult == 0) {
return showInfo1.getDay().compareTo(showInfo2.getDay());
}
return nameComparisonResult;
}
}
1: There are other ways to solve this instead using lot of if statements, but looks like that's outside the question scope. If not, edit the question and add it to show another ways to solve this.
Other tips for your current code:
Declare the names of the classes using CamelCase, where the first letter of the class name is Upper Case, so your showInfo class must be renamed to ShowInfo.
To access to the fields of a class, use proper getters and setters instead of marking the fields as public or leaving the with default scope. This mean, your ShowInfo class should become into:
public class ShowInfo {
private String name;
private String day;
private int time;
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
//similar for other fields in the class
}

Use selection sort algorithm which is easy to implement,
for (int i = 0; i < arr.length; i++)
{
for (int j = i + 1; j < arr.length; j++)
{
if (arr[i].time > arr[j].time) // Here ur code that which should be compare
{
ShowInfo temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
}
no need to check min element. go through this wiki http://en.wikipedia.org/wiki/Selection_sort

Why not you use a Collection for this sort of a thingy to work. Moreover, in your added example, you are simply changing one attribute of a given object, while sorting, though you not changing the position of the object as a whole, inside the given list.
Create a List which will contain the references of all the Shows, now compare each attribute of one Show with another, in the List. Once the algorithm feels like, that swapping needs to be done, simply pick the reference from the List, save it in a temp variable, replace it with a new reference at this location, and set duplicate to the one stored in the temp variable. You are done, List is sorted :-)
Here is one small example for the same, for help :
import java.io.*;
import java.util.*;
public class Sorter {
private BufferedReader input;
private List<ShowInfo> showList;
public Sorter() {
showList = new ArrayList<ShowInfo>();
input = new BufferedReader(
new InputStreamReader((System.in)));
}
private void createList() throws IOException {
for (int i = 0; i < 5; i++) {
System.out.format("Enter Show Name :");
String name = input.readLine();
System.out.format("Enter Time of the Show : ");
int time = Integer.parseInt(input.readLine());
ShowInfo show = new ShowInfo(name, time);
showList.add(show);
}
}
private void performTask() {
try {
createList();
} catch (Exception e) {
e.printStackTrace();
}
sortByTime(showList);
}
private void sortByTime(List<ShowInfo> showList) {
int min;
for (int i = 0; i < showList.size(); i++) {
// Assume first element is min
min = i;
for (int j = i+1; j < showList.size(); j++) {
if (showList.get(j).getTime() <
showList.get(min).getTime()) {
min = j;
}
}
if (min != i) {
ShowInfo temp = showList.get(i);
showList.set(i, showList.get(min));
showList.set(min, temp);
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < showList.size(); i++) {
System.out.println(showList.get(i).getName() +
" - " + showList.get(i).getTime());
}
}
public static void main(String[] args) {
new Sorter().performTask();
}
}
class ShowInfo {
private String name;
int time;
public ShowInfo(String n, int t) {
name = n;
time = t;
}
public String getName() {
return name;
}
public int getTime() {
return time;
}
}
EDIT 2 :
For sorting By Name you can use this function :
private void sortByName(List<ShowInfo> showList) {
int min;
for (int i = 0; i < showList.size(); i++) {
// Assume first element is min
min = i;
for (int j = i+1; j < showList.size(); j++) {
int value = (showList.get(j).getName()).compareToIgnoreCase(
showList.get(min).getName());
if (value < 0)
min = j;
}
if (min != i) {
ShowInfo temp = showList.get(i);
showList.set(i, showList.get(min));
showList.set(min, temp);
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < showList.size(); i++) {
System.out.println(showList.get(i).getName() +
" - " + showList.get(i).getTime());
}
}
EDIT 3 :
Added Comparable<?> Interface, to the existing class to perform sorting based on specified input. Though one can improve on the logic, by using Enumeration, though leaving it for the OP to try his/her hands on :-)
import java.io.*;
import java.util.*;
public class Sorter {
private BufferedReader input;
private List<ShowInfo> showList;
private int command;
public Sorter() {
showList = new ArrayList<ShowInfo>();
input = new BufferedReader(
new InputStreamReader((System.in)));
command = -1;
}
private void createList() throws IOException {
for (int i = 0; i < 5; i++) {
System.out.format("Enter Show Name :");
String name = input.readLine();
System.out.format("Enter Time of the Show : ");
int time = Integer.parseInt(input.readLine());
ShowInfo show = new ShowInfo(name, time);
showList.add(show);
}
}
private void performTask() {
try {
createList();
} catch (Exception e) {
e.printStackTrace();
}
System.out.format("How would you like to sort : %n");
System.out.format("Press 0 : By Name%n");
System.out.format("Press 1 : By Time%n");
try {
command = Integer.parseInt(input.readLine());
} catch (Exception e) {
e.printStackTrace();
}
sortList(showList);
}
private void sortList(List<ShowInfo> showList) {
int min;
for (int i = 0; i < showList.size(); i++) {
// Assume first element is min
min = i;
for (int j = i+1; j < showList.size(); j++) {
showList.get(j).setValues(command);
int value = showList.get(j).compareTo(showList.get(min));
if (value < 0) {
min = j;
}
}
if (min != i) {
Collections.swap(showList, i, min);
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < showList.size(); i++) {
System.out.println(showList.get(i).getName() +
" - " + showList.get(i).getTime());
}
}
public static void main(String[] args) {
new Sorter().performTask();
}
}
class ShowInfo implements Comparable<ShowInfo> {
private String name;
private int time;
private int command;
public ShowInfo(String n, int t) {
name = n;
time = t;
}
public String getName() {
return name;
}
public int getTime() {
return time;
}
public void setValues(int cmd) {
command = cmd;
}
public int compareTo(ShowInfo show) {
int lastCmp = 1;
if (command == 0) {
lastCmp = name.compareTo(show.name);
} else if (command == 1) {
if (time < show.time) {
lastCmp = -1;
} else if (time == show.time) {
lastCmp = 0;
} else if (time > show.time) {
lastCmp = 1;
}
}
return lastCmp;
}
}