We Keep Coding

java method find max price

My findmaxprice method returns the index of the first Car in the array with the maximum price. If it is not found, -1 is returned.
As far as I know, return will stop the for loop. Any advice on how to avoid it while keep the loop search for max price?
public int findmaxprice() {
double max =0;
for(int i =0; i < nCars; i++) {
if(max <= Cars[i].getPrice()) {
max = Cars[i].getPrice();
return i; //the problem is here
}
}
return -1;
}

You almost answered yourself - just don't return in the for loop.
public int findmaxprice() {
double max =0;
int maxIndex = -1;
for( int i =0; i < nCars; i++) {
if(max <= Cars[i].getPrice()) {
max = Cars[i].getPrice();
maxIndex = i;
}
}
return maxIndex;
}

Move the return statement outside of the loop
findmaxprice method: returns the index of the first Car in the array with the maximum price. If it is not found, -1 is returned. as far as i know, return will stop the for loop , any advice on how to avoid it while keep the loop search for max price ?
public int findmaxprice() {
double max =0;
for( int i =0; i < nCars; i++) {
if(max <= Cars[i].getPrice()) {
max = Cars[i].getPrice();
}
}
if(max != 0){
return max;
} else {
return -1;
}
}

The below method will fix your issue. Also, it gives you ability to specify a minimum price above which the car price will be considered for max calculation. You can keep this 0 in function call like findMaxPrice(0)if no such boundation needed.
public int findMaxPrice(int min) {
double max = min;
int maxPriceCarIndex = -1;
for (int i = 0; i < nCars; i++) {
if (max <= Cars[i].getPrice()) {
max = Cars[i].getPrice();
maxPriceCarIndex = i; //reassign the index here
}
}
return maxPriceCarIndex;
}

Maybe you just need the "most expensive" car and not the index of the car, then you could consider using streams
import java.util.Arrays;
import java.util.Comparator;
import java.util.Objects;
public class Test {
public static void main(String[] args) {
new Test().testGetMostExpensiveCar();
}
private void testGetMostExpensiveCar() {
// test null array
Car[] cars = null;
Car mostExpensive = getMostExpensiveCar(cars);
System.out.println(mostExpensive); // prints null
// test empty array
cars = new Car[10];
mostExpensive = getMostExpensiveCar(cars);
System.out.println(mostExpensive); // prints null
//test array with cars
cars[0] = new Car(10.0);
cars[5] = new Car(20.0);
cars[8] = new Car(30.0);
cars[8] = new Car(30.0);
mostExpensive = getMostExpensiveCar(cars);
System.out.println(mostExpensive);// prints Car [price=30.0]
}
/**
* #param cars
* #return the most Expensive car, null if the array is empty or no car is in
* the array
*/
public Car getMostExpensiveCar(Car[] cars) {
if (cars == null) {
return null;
}
return Arrays.stream(cars) // creates a Stream<Car> (take a look at e.g. https://www.baeldung.com/java-8-streams)
.filter(Objects::nonNull) // because there can be "null" values in the array
.max(Comparator.comparing(Car::getPrice)) // compares the car by price asc
.orElse(null); // return null if no element is found
}
private class Car {
private double price;
public Car(double price) {
super();
this.price = price;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
#Override
public String toString() {
return "Car [price=" + price + "]";
}
}
}

== null Doesn't work java

I have made a function for objects to reserve seats in a area. But if 2 objects enter the function at the same time they get the same seats. How do I solve this?
The Function getFreeChairs, returns the chair positions. And sets the Fan. But if two fans enter it at the same time they both get the same seats.
Sven
package model;
import actors.Fan;
import java.util.ArrayList;
import java.util.List;
/**
* Created by sveno on 12-10-2016.
*/
public class Vak {
private static int autoId = 1;
private String naam;
private int rijen, stoelenperrij, id;
private List<ArrayList> rows = new ArrayList<>();
private Fan fan = null;
public Vak(String naam, int rijen, int stoelenperrij) {
this.naam = naam;
this.rijen = rijen;
this.stoelenperrij = stoelenperrij;
this.id = autoId;
autoId++;
for (int i = 0; i < rijen; i++) {
rows.add(new ArrayList<Fan>());
}
for (ArrayList row : rows) {
for (int j = 0; j < stoelenperrij; j++) {
row.add(fan);
}
}
}
public void removeReserved(int rij, List<Integer> stoelen){
for (int i = 0; i < stoelen.size()-1; i++) {
//De reserveer alle stoelen
ArrayList<Fan> stoel = rows.get(rij);
stoel.set(stoelen.get(i),fan);
}
}
public int getRijen() {
return rijen;
}
public int getStoelenperrij() {
return stoelenperrij;
}
public List<ArrayList> getRows() {
return rows;
}
public int[] getFreeChairs(int aantalStoelen, Fan fan){
//Check for free seats
int count = 1;
int[] stoelenleeg = new int[aantalStoelen+1];
for (int j = 0; j < rows.size(); j++) {
for (int k = 0; k < rows.get(j).size(); k++) {
if (rows.get(j).get(k) == null){
stoelenleeg[count-1] = k;
count++;
//Not enough seats next to each other
if(count==aantalStoelen+1){
stoelenleeg[aantalStoelen] = j+1;
for (int o = 0; o < stoelenleeg.length-1; o++) {
ArrayList<Fan> stoel = rows.get(j);
stoel.set(stoelenleeg[o],fan);
}
return stoelenleeg;
}
}else{
//Not enough seats
stoelenleeg = new int[aantalStoelen+1];
count=1;
}
}
}
return stoelenleeg;
}
}

If your code is used in a concurrent context (multiple threads), you need to make sure that your code is thread safe.
It means that, only one single thread(person) should be able to call the getFreeChairs function(reserve a seat at a time)
The easy way to do it in java is to use the synchronized key word in the method definition:
public synchronized int[] getFreeChairs(int aantalStoelen, Fan fan){
...
}

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);

how to swap two array objects in java

I'm trying to sort courses and organize them by course number.
I have created an array of objects which contain 3 attributes (department, num, title). I want to sort this array by 'num' using the selection sort method. When i try to swap the two arrays the compiler says int cannot be converted to Course[].
public static void sortByNumber(Course[] arr){
int size = arr.length;
for (int i = 0; i < size - 1; i++) {
int min = i;
for (int j = i + 1; j < size; j++) {
if (arr[j].getNum() < arr[min].getNum()) {
min = j;
}
}
int temp = arr[i];
arr[i] = arr[min];
arr[min] = temp;
}
}
this is my other class.
public class Course {
//INSTANCE VARIABLES
private String dept = "";
private int num = 0;
private String title = "";
//CONSTRUCTORS
public Course(String dept, int num) {
this.dept = dept;
this.num = num;
}
public Course(String dept, int num, String title) {
this.dept = dept;
this.num = num;
this.title = title;
}
public Course() {
this.dept = "AAA";
this.num = 100;
this.title = "A course";
}
//SETTER AND GETTER METHODS
public void setDept(String dept) {
this.dept = dept;
}
public void setNum(int num) {
this.num = num;
}
public void setTitle(String title) {
this.title = title;
}
public String getDept() {
return this.dept;
}
public int getNum() {
return this.num;
}
public String getTitle() {
return this.title;
}
}

int temp = arr[i];
arr[i] is Course, temp is int. You cannot assign a Course into an int variable, neither can you assign an int into a Course variable, because they are two completely different types.
Make your temp a Course:
Course temp = arr[i];

Ishamael's answer was correct. I will throw out this addition as you later may find it very useful to allow the user to sort by any field:
First you will need to add the Comparable interface to your Course class and write the compareTo() method. I've added an enum to the class to match each field you might want to sort by:
public class Course implements Comparable<Course>{
public static enum SortBy {
DEPARTMENT,
COURSE_NUM,
TITLE,
NOT_SORTED;
}
public static SortBy sortBy = SortBy.NOT_SORTED;
#Override
public int compareTo(Course course) {
if(sortBy == SortBy.DEPARTMENT) return getDept().compareTo(course.getDept());
if(sortBy == SortBy.COURSE_NUM) return getNum() - course.getNum();
if(sortBy == SortBy.TITLE) return getTitle().compareTo(course.getTitle());
return 0;
}
...
You can now modify your 'if' statement in your sort method to:
if (arr[j].compareTo(arr[min]) < 0) {
min = j;
}
Here is an example of using it now...
public static void main(String[] args) {
Course[] arr = {
new Course("dep-B", 3, "title-F"),
new Course("dep-C", 1, "title-E"),
new Course("dep-A", 2, "title-D")
};
System.out.println("Sorted by default (not sorted)");
System.out.println(Arrays.toString(arr));
System.out.println("Sorted by Department");
Course.sortBy = SortBy.DEPARTMENT;
sortByNumber(arr);
System.out.println(Arrays.toString(arr));
System.out.println("Sorted by Course Number");
Course.sortBy = SortBy.COURSE_NUM;
sortByNumber(arr);
System.out.println(Arrays.toString(arr));
System.out.println("Sorted by Title");
Course.sortBy = SortBy.TITLE;
sortByNumber(arr);
System.out.println(Arrays.toString(arr));
}

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;
}
}