Develop Reference

How do I update a users input in an arraylist?

So I'm making a program for a car dealership as my final project for my class. At this time I'd say I'm about 75% done, but I am having trouble figuring out how to update the users input in an array list. So each array list slot contains the year, make, model, color, and mileage of a car. I can add a new car, I can remove a car, and I can quit my program. I have tried many things, I've read many papers, blogs, forums, and my book for class, but its always updating with the programmers input.
package carDealer;
import java.util.ArrayList;
import java.util.Scanner;
public class VehicleInformation {
public static void main(String [] args) {
Scanner scnr = new Scanner(System.in);
ArrayList<VehicleInventory> car = new ArrayList<VehicleInventory>();
String userInput = "-";
while (!userInput.equals("q")) {
System.out.println("Commands: 'a' to add, 'd' to delete, 'e' to edit, 'q' to quit");
userInput = scnr.next();
if (userInput.equals("a")) {
System.out.println("Year: ");
int year = scnr.nextInt();
System.out.println("Make: ");
String make = scnr.next();
System.out.println("Model: ");
String model = scnr.next();
System.out.println("Color: ");
String color = scnr.next();
System.out.println("Mileage: ");
int mileage = scnr.nextInt();
VehicleInventory userCar = new VehicleInventory();
userCar.setMake(make);
userCar.setModel(model);
userCar.setYear(year);
userCar.setColor(color);
userCar.setMileage(mileage);
userCar.print();
addCar(car, userCar);
}
if (userInput.equals("d")) {
for (int i = 0; i < car.size(); ++i) {
System.out.print((i + 1) + " ");
car.get(i).print();
}
System.out.println("List number: ");
int userNum = scnr.nextInt();
car.remove(userNum - 1);
System.out.println("count: " + car.size());
}
if (userInput.equals("e")) {
for (int i = 0; i < car.size(); ++i) {
System.out.print((i + 1) + " ");
car.get(i).print();
}
System.out.println("List number: ");
int userNum = scnr.nextInt();
car.get(userNum - 1);

You can just do a loop to look up for the car model the user wants to update (it can be any other attribute), and once found update it's value with the desired one:
String vehicleToLookUp = "golf"; // This will be received by user input
String vehicleNewName = "golf gti"; // This will be received by user input
for( int i = 0; i < car.size(); i++){
if(vehicleToLookUp.getModel().equals(car.get(i)){
car.get(i).setSomeAttribute(...); // Set the desired attribute here
}
}
Or if you want to substitute the whole object...
String vehicleToLookUp = "golf"; // This will be received by user input
VehicleInventory newVehicle = new VehicleInventory(); // You will set the attributes by user input
for( int i = 0; i < car.size(); i++){
if(vehicleToLookUp.getModel().equals(car.get(i)){
car.set(i, newVehicle ); // Create your object and pass it here
}
}
Also, instead of all those if, you could use if/else if or even a switch/case for better performance/readability (think that even if your logic is true for first if, it will check for all the other if you created, wasting time and processing power.

2D String search in Java

This is my code:
import java.util.*;
import java.util.Arrays;
public class PhoneNumbers
{
static Scanner scan = new Scanner(System.in);
public static void main(String[] args)
{
String phoneList[][] =
{
{"Harrison, Rose: ", "James, Jean: ", "Smith, William: ", "Smith, Brad: "},
{"415-555-2234", "415-555-9098", "415-555-1785", "415-555-9224"}
};
System.out.println(Arrays.deepToString(phoneList)); //this line is to make sure the 2D arrays work
String input;
System.out.print("Enter the first few letters of a last name to search for: ");
input = scan.nextLine();
int match = -1;
for(int i = 0; i < phoneList.length; i++)
{
if(phoneList[i].indexOf(input))
{
System.out.println(phoneList[i]);
match = i;
break;
}
else
System.out.println("There is no match.");
}
}
}
My goal is:
I have a 2D array, i got name in one and the phone number in another.
I am trying to allow user to enter first few letters of a last name and do a search that and display the matching search along with the phone number(this would be my next challenge).
Thank you,

Here is your Answer :
import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.util.Scanner;
public class Test {
public static void main(String[] args) {
int refNumber=-1;
String phoneList[][] =
{
{"Harrison, Rose: ", "James, Jean: ", "Smith, William: ", "Smith, Brad: "},
{"415-555-2234", "415-555-9098", "415-555-1785", "415-555-9224"}
};
Scanner scanner = new Scanner(System.in);
System.out.print("Enter String to be searched ->");
String input = scanner.nextLine();
//System.out.println(input);
for (int i=0; i<phoneList[0].length; i++) {
if (phoneList[0][i].contains(input)) {
refNumber = i;
}
}
System.out.println("Name ->"+phoneList[0][refNumber]);
System.out.println("Phone No ->"+phoneList[1][refNumber]);
}
}

Create a dictionary (e.g. trie tree) for all the names you have. While creating/updating your search dictionary, at each node, keep an integer array which gives you the list of index of all the matching names. As the user provides input, you can keep on refining the result at runtime, and when he selects any one of the provided suggestions, you'll have the index to it.
Rest is simple, using that index, display the phone number of the selected person.

I did some refactoring:
using a Map: name => phone
public static void main(String[] args)
{
String phoneList[][] =
{
{"Harrison, Rose: ", "James, Jean: ", "Smith, William: ", "Smith, Brad: "},
{"415-555-2234", "415-555-9098", "415-555-1785", "415-555-9224"}
};
// Make a Map
Map<String,String> mss=new HashMap<String,String>();
for(int i = 0; i < phoneList.length; i++)
mss.put(phoneList[0][i], phoneList[1][i]) ;
String input;
System.out.print("Enter the first few letters of a last name to search for: ");
Scanner scan = new Scanner(System.in);
input = scan.nextLine();
String match="";
for (String name: mss.keySet())
if (name.startsWith(input))
{
System.out.println("NAME:"+name+ " PHONE:"+mss.get(name));
match=name;
break;
}
if (match.equals(""))
System.out.println("There is no match.");
}

One simple approach is to match the beginning of the input String:
for(int x=0; x<phoneList[1].length; x++)
if(phoneList[0][x].toLowerCase().startsWith(input.toLowerCase()))
System.out.println("Numbers which matched: " + phoneList[1][x]);
Program output:
//Using "smith" as input:
Numbers which matched: 415-555-1785
Numbers which matched: 415-555-9224

Using a scanner input to define the number of scanner inputs required

I have made it a little further. It turns out I can use loops but not arrays in my assignment. So here's the current version (keep in mind no final calculations or anything yet.) So if you look at the homework method, you can see I am asking for the "number of assignments." Now, for each assignment, I need to ask for and sum both the Earned Score and the Maximum Possible Score. So for instance, if there were 3 assignments, they might have earned scores of 18, 22, and 29, and maximum possible scores of 20, 25, and 30 respectively. I need to grab both using the console, but I don't know how to get two variables using the same loop (or in the same method).
Thanks in advance for your help!
import java.util.*;
public class Grades {
public static void main(String[] args) {
welcomeScreen();
weightCalculator();
homework();
}
public static void welcomeScreen() {
System.out.println("This program accepts your homework scores and");
System.out.println("scores from two exams as input and computes");
System.out.println("your grade in the course.");
System.out.println();
}
public static void weightCalculator() {
System.out.println("Homework and Exam 1 weights? ");
Scanner console = new Scanner(System.in);
int a = console.nextInt();
int b = console.nextInt();
int c = 100 - a - b;
System.out.println();
System.out.println("Using weights of " + a + " " + b + " " + c);
}
public static void homework() {
Scanner console = new Scanner(System.in);
System.out.print("Number of assignments? ");
int totalAssignments = console.nextInt();
int sum = 0;
for (int i = 1; i <= totalAssignments; i++) {
System.out.print(" #" + i + "? ");
int next = console.nextInt();
sum += next;
}
System.out.println();
System.out.println("sum = " + sum);
}
}

I don't know where exactly your problem is, so I will try to give you some remarks. This is how I would start (of course there are other ways to implement this):
First of all - create Assignment class to hold all informations in nice, wrapped form:
public class Assignment {
private int pointsEarned;
private int pointsTotal;
public Assignment(int pointsEarned, int pointsTotal) {
this.pointsEarned = pointsEarned;
this.pointsTotal = pointsTotal;
}
...getters, setters...
}
To request number of assignments you can use simply nextInt() method and assign it to some variable:
Scanner sc = new Scanner(System.in);
int numberOfAssignments = sc.nextInt();
Then, use this variable to create some collection of assignments (for example using simple array):
Assignment[] assignments = new Assignment[numberOfAssignments];
Next, you can fill this collection using scanner again:
for(int i = 0; i < numberOfAssignments; i++) {
int pointsEarned = sc.nextInt();
int pointsTotal = sc.nextInt();
assignments[i] = new Assignment(pointsEarned, pointsTotal)
}
So here, you have filled collection of assignments. You can now print it, calculate average etc.
I hope above code gives you some remarks how to implement this.

How do I use same variable inside two different methods without making those variables global?

My simple program will ask user to enter few cities. The user should be able to print them out by choosing another option.
Now I have declared an array inside a method (city();) to store those values. And I have two different methods each for asking user and printing them out (which is gonna be called in main class). If I want to print out the array (in printCity() method ), it must use the varibale which is used in another method ( city();). Thus, the printCity() method shows error that it can't find the variables. Besides, declaring those variable as Global (outside the methods)doesn't work in my case (I don't know why).
So, how can I fix this issue so that same variables works in two different methods?
My code:
Main class:
package city;
import java.util.*;
public class City {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
UserInput ui = new UserInput();
System.out.println(" THIS PROGRAM WILL TELL YOU THE CITY YOU HAVE EVER TRAVELLED\n"
+ " Choose one of the following option\n\n"
+ " You must enter city name before printing them out!");
System.out.println("1. Enter the cities you have travelled\n"
+ "2. Print out the cities\n"
+ "3. Exit\n"
+ "....................\n"
+ "....................");
while (true) {
int userChoose = input.nextInt();
switch (userChoose) {
case 1:
//call method where the program asks to enter city name
ui.city();
break;
case 2:
//call method where the program prints out the city name
ui.printCity();
break;
case 3:
System.exit(0);
default:
System.out.println("Invalid input! Plz try again: ");
}
}
}
}
UserInput class:
package city;
import java.util.*;
public class UserInput {
Scanner inScanner = new Scanner(System.in);
public void city() {
System.out.println("How many favourite city you have in your list?");
int numOfCity = inScanner.nextInt();
String[] cityInArr = new String[numOfCity];
for (int i = 0; i < numOfCity; i++) {
System.out.println("City " + (i + 1) + ": ");
cityInArr[i] = inScanner.next();
}
System.out.println("YOU ARE DONE! NOW PRINT THEM OUT");
}
public void printCity() {
System.out.println("");
System.out.println("These are your favorite cities: ");
for (int j = 0; j < numOfCity; j++) {//has an error
System.out.printf("%s ", cityInArr);//has an error
}
}
}

It sounds like your city() method should return the array of cities, which you can then pass to the printCity() method:
public String[] city() {
...
return cityInArr;
}
public void printCity(String[] cities) {
...
}
And in your calling code:
String[] cities = {}; // Empty until fetched
...
cities = ui.city();
...
ui.printCity(cities);
I would also strongly recommend that you revisit your naming. For example, getFavoriteCities() and displayCities() would be more appropriate, IMO.

Assuming that by 'global', you mean declaring them as a field of the UserInput class (correct me if you mean something else), I fail to understand why you wouldn't want to do that.
Considering you are sharing data between two methods of the same instance of the same class, a field is exactly what you need..
I took the liberty of rewriting your UserInput class to have the array as a field (the main class works unchanged). Also note that you don't need to pass around the number of cities, as it is determined by the length of the array.
public class UserInput {
private String[] cityInArr;
public void city() {
System.out.println("How many favourite city you have in your list?");
Scanner inScanner = new Scanner(System.in);
int numOfCity = inScanner.nextInt();
cityInArr = new String[numOfCity];
for (int i = 0; i < numOfCity; i++) {
System.out.println("City " + (i + 1) + ": ");
cityInArr[i] = inScanner.next();
}
System.out.println("YOU ARE DONE! NOW PRINT THEM OUT");
}
public void printCity() {
System.out.println("\nThese are your favorite cities: ");
for (int j = 0; j < cityInArr.length; j++) {//has an error
System.out.printf("%s ", cityInArr[j]);//has an error
}
}
}

You need to pass the it as method argument.
public void printCity(String[] cityInArr, int numOfCity) {
System.out.println("");
System.out.println("These are your favorite cities: ");
for (int j = 0; j < numOfCity; j++) {//has an error
System.out.printf("%s ", cityInArr);//has an error
}
Then call it like this
public static void main(String[] args) {
.......
printCity(cityArray, numOfCity);
........
}

Counting the occurrence of objects in an ArrayList, using either Collections or my functions

I have an ArrayList of FlowerClass objects. Each of these FlowerClass objects has a name. I want to go through the ArrayList and count them. I want to display the amount of each. So if I have three FlowerClass objects named Rose, two named Daffodil, and one named Tulip...I want to display the following:
Found 3 Rose
Found 3 Daffodil
Found 3 Tulip
So far, I've gotten it to count correctly using two functions I made. The problem is that I iterate through the entire ArrayList...so it'll show me the results more than once. For example, if the user adds 3 Roses and 2 Daffodils...The output is like this:
Found 3 Roses
Found 3 Roses
Found 3 Roses
Found 2 Daffodils
Found 2 Daffodils
I know why the code does this but I don't know how to erase repeats of output. I also don't know how to implement Collections correctly. I've used Collections on an ArrayList of strings before...and it works. But this time I'd be using Collections on an ArrayList of Objects, and I want to check for the frequency of each specific name. Here is the main class:
import java.util.Scanner;
import java.util.ArrayList;
import java.util.Collections;
public class MainClass {
static ArrayList<FlowerClass> flowerPack = new ArrayList<FlowerClass>();
public static void main(String[] args){
Scanner input = new Scanner(System.in);
while(true){
System.out.println("1. Add flower to flowerpack.");
System.out.println("2. Remove flower from the flowerpack.");
System.out.println("3. Search for a flower in the flowerpack.");
System.out.println("4. Display the flowers in the flowerpack.");
System.out.println("5. Exit the program.");
int userChoice = input.nextInt();
switch(userChoice){
case 1:
addFlower();
break;
case 2:
searchFlower();
break;
case 3:
displayFlowers();
break;
case 4:
System.out.println("Goodbye!");
System.exit(0);
}
}
}
public static void addFlower(){
if (FlowerClass.numberFlowers() == 25){
System.out.println("There are 25 flowers in the flowerpack. Remove at least one in order to add more.");
return;
}
Scanner input = new Scanner(System.in);
System.out.println("What is the flower's name?");
String desiredName = input.nextLine();
System.out.println("What is the flower's color?");
String desiredColor = input.nextLine();
System.out.println("How many thorns does it have?");
Scanner input2 = new Scanner(System.in);
int desiredThorns = input2.nextInt();
System.out.println("What does it smell like?");
String desiredSmell = input.nextLine();
flowerPack.add(new FlowerClass(desiredName, desiredColor, desiredThorns, desiredSmell));
}
public static void searchFlower(){
System.out.println("Enter the flower you want to search for.");
Scanner input = new Scanner(System.in);
String userChoice = input.nextLine();
int occurrences = 0;
for (FlowerClass flower: flowerPack){
String name = flower.getName();
if (userChoice.equals(name)){
occurrences++;
}
else if(occurrences == 0){
System.out.println("Match not found.");
return;
}
}
System.out.println("Found " + occurrences + " " + userChoice);
}
public static void searchFlower(String desiredFlower){
int occurrences = 0;
String userChoice = desiredFlower;
for (FlowerClass flower: flowerPack){
String name = flower.getName();
if (userChoice.equals(name)){
occurrences++;
}
}
System.out.println("Found " + occurrences + " " + userChoice);
}
public static void displayFlowers(){
int repeats = 0;
/*for (FlowerClass flower: flowerPack){
System.out.println(flower.getName());
}
System.out.println("Number of flowers in pack: " + FlowerClass.numberFlowers());*/
//int occurrences = Collections.frequency(flowerPack, name);
//System.out.println(name + ": " + occurrences);
for (FlowerClass flower: flowerPack){
String name = flower.getName();
searchFlower(name);
}
}
}
Here is the FlowerClass:
public class FlowerClass {
public static int numberOfFlowers = 0;
public String flowerName = null;
public String flowerColor = null;
public int numberThorns = 0;
public String flowerSmell = null;
FlowerClass(){
}
FlowerClass(String desiredName, String desiredColor, int desiredThorns, String desiredSmell){
flowerName = desiredName;
flowerColor = desiredColor;
numberThorns = desiredThorns;
flowerSmell = desiredSmell;
numberOfFlowers++;
}
public void setName(String desiredName){
flowerName = desiredName;
}
public String getName(){
return flowerName;
}
public static int numberFlowers(){
return numberOfFlowers;
}
}
If you look at my last function in the main class, you'll see that I commented out the way I was attempting to implement Collections.frequency. I also tried making a multidimensional array of Strings and storing the names of the flowers and also the number of flowers in the arrays. This was counting everything correctly but I wasn't sure how to display the names alongside the counts. It was getting very messy so I abandoned that attempt for now in favor of trying these other two options. If I can find a way to erase repeated lines of output (or if I can find a way to get Collections to work) then I won't need to tinker with the multidimensional array.
Any tips would be very much appreciated. Thank you for your time.

Interesting code, but it doesn't work the way I would do it.
In this current case as you've done it, you would need to keep track of the flower names you have already encountered:
public static void displayFlowers(){
//int repeats = 0;
List<String> displayedFlowerTypes = new ArrayList<String>();
for (FlowerClass flower: flowerPack){
String name = flower.getName();
if(!displayedFlowerTypes.contains(name))
{
displayedFlowerTypes.add(name);
searchFlower(name);
}
}
}
What I would rather do is maintain a Map that keeps track of the counts of the flower types, and just obtain the numbers for the types from that:
public class MainClass {
static List<FlowerClass> flowerPack = new ArrayList<FlowerClass>();
static Map<String, Integer> flowerCount = new HashMap<String, Integer>();
public static void addFlower() {
if (FlowerClass.numberFlowers() == 25) {
System.out.println("There are 25 flowers in the flowerpack. Remove at least one in order to add more.");
return;
}
Scanner input = new Scanner(System.in);
System.out.println("What is the flower's name?");
String desiredName = input.nextLine();
System.out.println("What is the flower's color?");
String desiredColor = input.nextLine();
System.out.println("How many thorns does it have?");
Scanner input2 = new Scanner(System.in);
int desiredThorns = input2.nextInt();
System.out.println("What does it smell like?");
String desiredSmell = input.nextLine();
flowerPack.add(new FlowerClass(desiredName, desiredColor, desiredThorns, desiredSmell));
if(!flowerCount.containsKey(desiredName))
{
flowerCount.put(desiredName, 1);
}
else
{
int currentCount = flowerCount.get(desiredName);
flowerCount.put(desiredName, currentCount+1));
}
}
That way, you could just display the flowers as the following:
public static void displayFlowers() {
for (String name : flowerCount.keySet()) {
//searchFlower(name);
System.out.println("Found " + flowerCount.get(name) + " " + name);
}
}

You could put your Flower(s) in a Set. But the easiest solution I can think of is to sort your flowers. So first, implement a Comparator<FlowerClass>
public static class FlowerComparator implements Comparator<FlowerClass> {
#Override
public int compare(FlowerClass o1, FlowerClass o2) {
return o1.getName().compareTo(o2.getName());
}
}
Then you can sort with Collections.sort(List, Comparator)
FlowerComparator flowerComparator = new FlowerComparator();
Collections.sort(flowerPack, flowerComparator);
And then your for loop needs to be something like this (to stop searching for the same flower),
String lastName = null;
for (int i = 0; i < flowerPack.size(); i++){
FlowerClass flower = flowerPack.get(i);
String name = flower.getName();
if (lastName == null || !lastName.equals(name)) {
lastName = name;
searchFlower(name); // or return the number found, and then add that count to i.
}
}