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Java - Looping through ArrayList to scan for matching value [duplicate]

This question already has answers here:
Iterating through a Collection, avoiding ConcurrentModificationException when removing objects in a loop
(31 answers)
Closed 6 years ago.
I'm trying to write a simple program using an ArrayList that adds values, removes values, and prints values. However, I'm having an issue with removing values that the user inputs. The user should input a designated amount of values (determined by the user) and then the program should remove those values (if there are duplicates then it should just remove the first instance of the number which is fine). It's not removing the values and in some cases removes one value. I'm a bit confused as to where my code is bugged. Here is my code for remove values:
private static void removeVals() {
System.out.println("How many values would you like to remove?");
int amountToRemove = scanner.nextInt();
scanner.nextLine();
System.out.println("Enter " + amountToRemove + " values:");
for(int i = 0; i < amountToRemove; i++) {
int vals = scanner.nextInt();
if(arrayList.get(i).equals(vals)) {
arrayList.remove(i);
}
}
System.out.println("Values removed");
}
And here is my full code:
public class Main {
private static ArrayList<Integer> arrayList = new ArrayList<Integer>();
private static Scanner scanner = new Scanner(System.in);
public static void main(String[] args) {
printOptions();
int option = scanner.nextInt();
while (option != 0) {
switch(option) {
case 1:
addVals();
printOptions();
option = scanner.nextInt();
break;
case 2:
removeVals();
printOptions();
option = scanner.nextInt();
break;
case 3:
printVals();
printOptions();
option = scanner.nextInt();
break;
case 4:
printOptions();
printOptions();
option = scanner.nextInt();
break;
default:
System.out.println("Not a valid option, please enter again:");
option = scanner.nextInt();
break;
}
}
}
private static void addVals() {
System.out.println("How many values would you like to add?");
int amountToAdd = scanner.nextInt();
scanner.nextLine();
System.out.println("Enter " + amountToAdd + " values:");
for(int i = 0; i < amountToAdd; i++) {
int vals = scanner.nextInt();
arrayList.add(vals);
}
}
private static void removeVals() {
System.out.println("How many values would you like to remove?");
int amountToRemove = scanner.nextInt();
scanner.nextLine();
System.out.println("Enter " + amountToRemove + " values:");
for(int i = 0; i < amountToRemove; i++) {
int vals = scanner.nextInt();
if(arrayList.get(i).equals(vals)) {
arrayList.remove(i);
}
}
System.out.println("Values removed");
}
private static void printVals() {
for(int i = 0; i < arrayList.size(); i++) {
System.out.print(arrayList.get(i) + " ");
}
System.out.println();
}
private static void printOptions() {
System.out.println();
System.out.println("Program options: ");
System.out.println("1. Add values\n2. Remove values\n3. Print values\n4. Print options\n0. Exit\n");
System.out.println("\nWhat would you like to do? (enter an option):");
}
}

arrayList.remove(i) removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).
that is the bug your code
for more details refer below link
https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#remove(int) ,

Java array and nextInt(); do not work properly

Hello guys I am having a problem with an array and a .nextInt(); this is causing my output line at the 3rd prompt to shift up instead of under, and seriously cannot figure out what's wrong.
I have tried .hasNextInt(); but nothing, it actually gives me an error, so here is the code:
import java.util.Random;
import java.util.Scanner;
public class birthday {
public static void main(String[] args) {
System.out.println("Welcome to the birthday problem Simulator\n");
String userAnswer="";
Scanner stdIn = new Scanner(System.in);
do {
int [] userInput = promptAndRead(stdIn); //my problem
double probability = compute(userInput[0], userInput[1]);
// Print results
System.out.println("For a group of " + userInput[1] + " people, the probability");
System.out.print("that two people have the same birthday is\n");
System.out.println(probability);
System.out.print("\nDo you want to run another set of simulations(y/n)? :");
//eat or skip empty line
stdIn.nextLine();
userAnswer = stdIn.nextLine();
} while (userAnswer.equals("y"));
System.out.println("Goodbye!");
stdIn.close();
}
// User input prompt where you make the simulation. For people and return them as an array
public static int[] promptAndRead(Scanner stdIn)
{
System.out.println("Please enter the number of simulations you want to do: ");
int[] userInput =new int [2]; //my problem
userInput[0]= stdIn.nextInt(); //my problem
System.out.println("Please enter the size of the group you want : ");
int[] userInput1 = new int [2];
userInput[1] = stdIn.nextInt();
int a = userInput[1];
while (a<2 || a>365)
{
System.out.println("please type the number that is between 2~365");
}
System.out.println();
return promptAndRead(stdIn);
}
// Method for calculations
public static double compute(int numOfSimulation, int numOfPeople)
{
for (int i =0; i < numOfPeople; i++)
{
Random rnd = new Random(1);
//Generates a random number between 0 and 364 exclusive
int num = rnd.nextInt(364);
System.out.println(num);
System.out.println(num / 365 * numOfPeople * numOfSimulation);
}
return numOfPeople;
}
}

Found it!!!!!!!!!!!
do this:
// User input prompt where you make the simulation. For people and return them as an array
public static int[] promptAndRead(Scanner stdIn)
{
System.out.println("Please enter the number of simulations you want to do: ");
int[] userInput =new int [2]; //CHANGE THIS TO 1?
userInput[0]= stdIn.nextInt(); //my problem
System.out.println("Please enter the size of the group you want : ");
int[] userInput1 = new int [2]; //CHANGE THIS TO 1?
userInput[1] = stdIn.nextInt();
int a = userInput[1];
while (a<2 || a>365)
{
System.out.println("please type the number that is between 2~365");
}
System.out.println();
return(userInput);
}
To return the array
Let me know!

I actually don't think you can do it there with that userInput, I am saying this because the methodology of doing this program is quite arcane.
You are then calling 2 arrays at prompting, I wonder if you might change that to one what will change such as:
// User input prompt where you make the simulation. For people and return them as an array
public static int[] promptAndRead(Scanner stdIn)
{
System.out.println("Please enter the number of simulations you want to do: ");
int[] userInput =new int [2]; //CHANGE THIS TO 1?
userInput[0]= stdIn.nextInt(); //my problem
System.out.println("Please enter the size of the group you want : ");
int[] userInput1 = new int [2]; //CHANGE THIS TO 1?
userInput[1] = stdIn.nextInt();
int a = userInput[1];
while (a<2 || a>365)
{
System.out.println("please type the number that is between 2~365");
}
System.out.println();
return promptAndRead(stdIn);
}
As also the return promptAndRead(stdIn); might be part of the problem
Don't know though just trowing suggestions at Markov ;)

Filling a specifc part of a multidimensional string array(Out of bounds)

I'm making a database where you can enter in animals and the supplements that they need. I have to use a multidimensional array. The problem I'm running into is that when a user goes into entering data into the multidimensional array, I get an out of bounds error. I'm confused because I used the same methodology for the user to input the type of animal and the number of supplements needed, but when it gets to actually entering the supplement, I introduced and array hold to keep the supplements for each animal organized. For a more visual reference, my logic wanted to be like this:
Names
Animal Type 1 Supplement 1
The Animal types go down the first column while the supplements fill in a horizontal fashion on each animal. I'll post my code but specifically I've run into issues with the array out of bounds. I suspect it has to do with how I initialized the multi array, but I'm unsure at this point. Any help would be greatly appreciated!
//Nicholas Stafford
//February 1, 2016
//This program will allow user input of up to any number of animals and dietary information and then allow the user to display that information when searching the database
import java.util.Scanner;
import java.util.Arrays;
public class inventory {
public static void main(String[] args)
{
//Initial variables
int choiceent;
int numAnimals = 0;
int numDiet = 0;
int ArrayHold = 0;
boolean isNum;
boolean isNum2;
boolean quit = false;
//Scanners needed for input
Scanner choice = new Scanner(System.in);
Scanner input1 = new Scanner(System.in);
Scanner input2 = new Scanner(System.in);
Scanner input3 = new Scanner(System.in);
Scanner input4 = new Scanner(System.in);
//Initial value needed to enter animals into database
System.out.println("Enter the number of animals you wish to enter:");
do
{
if(input1.hasNextInt()) {
numAnimals = input1.nextInt();
isNum = true;
}
else {
System.out.println("Please enter an integer value!");
isNum = false;
input1.next();
}
}
while(!(isNum));
System.out.println("You are entering " +numAnimals+ " animals.");
//Multidimensional array
String [][] ZooBase = new String [100][100];
//Array for data types
int numDietA[] = new int [numAnimals];
do{
System.out.println("1. Enter the names of each animal");
System.out.println("2. Enter the dietary information");
System.out.println("3. Search the array for information");
System.out.println("4. Close the program");
choiceent = choice.nextInt();
switch(choiceent)
{
case 1:
//Data validation for name
for(int i = 0; i < numAnimals; i++)
{
System.out.println("Enter the type of animal for animal " +i+ "");
while(!input2.hasNext("[a-zA-Z]+"))
{
System.out.println("Enter a type of animal!");
ZooBase[i+1][0] = input2.nextLine();
}
ZooBase[i+1][0] = input2.nextLine();
}
//Display Names
System.out.println("Names");
for(int j = 0; j < numAnimals; j++){
System.out.println(ZooBase[j+1][0]);
}
break;
case 2:
for(int j = 0; j < numAnimals; j++)
{
System.out.println("How many supplements does the " +ZooBase[j+1][0]+ " need?");
do
{
if(input3.hasNextInt()) {
numDietA[j] = input3.nextInt();
isNum2 = true;
}
else {
System.out.println("Please enter an integer value!");
isNum2 = false;
input3.next();
}
}while(!(isNum2));
}
for(int k = 0; k < numAnimals; k++)
{
ArrayHold = k+1;
for(int m = 0; m < numDietA[m]; m++ )
{
System.out.println("Enter item " +m+ " for the " +ZooBase[m+1][0]+ "");
while(!input4.hasNext("[a-zA-Z]+"))
{
System.out.println("Enter a supplement (No integers)!");
ZooBase[ArrayHold][m+2] = input4.nextLine();
}
ZooBase[ArrayHold][m+2] = input4.nextLine();
}
}
break;
case 3:
break;
case 4:
quit = true;
break;
default:
System.out.println("Invalid option!");
break;
}
}while(choiceent != 4);
}
}

Once an array is initialized, its size can't be changed. To make sure this does not happen, use ArrayList<>, which does not have fixed bounds. You can find the syntax + all details here: https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html
Hope that helps!
ps. you can also initialize just 1 scanner input and use it throughout

How do I output a TABLE with names and scores with only using Arrays and Methods?

I have been trying to find the answer to this question but to no avail!
Basically I have to write a program where 'x' number of players can enter a guessing game and input their guesses and then get a score.
However, right after they input their guesses, i have to output it in a table form like this "NAME GUESS SCORE"
I do not know how i can do this with a for loop since a for loop println can only print values from playersArray. How can I print another array like guessesArray to the side of it?
I can only use Arrays and Methods to do this.
Below I will show u what i have right now:
import java.util.Scanner;
import java.util.Random;
import java.lang.Math;
public class game
{
static int[] guessesArray;
static int guess;
static String [] playersArray;
static int[] currscoresArray;
static int [] addscoresArray;
static int [] finalscoresArray;
public static void main(String [] args){
System.out.print("Number of players? ");
Scanner kb = new Scanner(System.in);
int numplayers = kb.nextInt();
//Initialize
playersArray = new String[numplayers];
guessesArray = new int [numplayers];
currscoresArray = new int [numplayers];
addscoresArray = new int [numplayers];
finalscoresArray = new int [numplayers];
populateArray(playersArray);
displayMenu();
}
public static void populateArray( String[] x){
Scanner kb = new Scanner(System.in);
for (int i = 0; i<x.length ; i++){
System.out.print("Enter Player "+(i+1)+": ");
x[i]=kb.nextLine();
}
}
public static void displayMenu(){
int choice=0;
Scanner kb = new Scanner(System.in);
String[] args = {};
while(true){
System.out.println("Menu ");
System.out.println("1. Make Guess");
System.out.println("2. List Winner");
System.out.println("0. Exit");
System.out.print("Enter choice: ");
choice = kb.nextInt();
if (choice==0){
System.out.print("Do you want to play a new game? Y/N: ");
String ans = kb.next();
if (ans.equals ("Y") || ans.equals ("y")){
main(args);
}
break;
}
switch (choice){
case 1: makeGuess(); break;
case 2: listWinner(); break;
default: System.out.println("Invalid choice");
}
}
System.out.println("End of program");System.exit(0);
}
public static void makeGuess(){
Scanner kb = new Scanner(System.in);
Random rand = new Random();
int secret = rand.nextInt(10)+1;
for (int i=0; i < guessesArray.length; i++){
System.out.print("Enter your guess "+playersArray[i]+": ");
guessesArray[i]=kb.nextInt();
}
int diff = (int)(Math.abs(guess - secret));
int score=0;
if (diff == 0){
score=score+10;
}else if(diff<=1){
score=score+5;
}else if(diff<=2){
score=score+2;
}
for (int i=0; i< currscoresArray.length; i++){
currscoresArray[i]=score;
}
System.out.println();
System.out.println("Generated number is "+secret);
System.out.println("Current Score Listing");
System.out.println(" Name Guess Score Added Final Score");
System.out.println("1. "+playersArray[0]+" \t "+guessesArray[0]+" \t"+currscoresArray[0]+"");
System.out.println("1. "+playersArray[1]+" \t "+guessesArray[1]+" \t"+currscoresArray[1]+"");
}
public static void listWinner(){
}
}

just reuse a int x variable when printing from each array?
for( int x = 0; x < playersArray.length; x++ ) {
System.out.println( playersArray[ x ] + ” ” + guessArray[ x ] + " " + finalScoresArray[ x ] );
}
you already give an example in your code where you print the 3 values with a single print method. you used a for loop for indexing an element in an array. So combing the 2 techniques shouldn't be too difficult to grasp.

Instead of using an enhanced for loop (e.g. for (String player : playersArray) {}, you can use an indexed one:
for (int i = 0; i < playersArray.length; i++) {
String name = playerArray[i];
double score = scoresArray[i];
}
That being said, you should really make a Player class, that holds all information of a single player, and then have just one array, of that type. That's much nicer, not only because you can use enhanced fors, but because you don't need to make sure the arrays are always synced, and your code becomes way easier to understand.

Store/ Display Data Inputs from Arrays

I'm having problems on how and where to put arrays.
I figured out how and where to put a loop so it will keep on gathering multiple user data that will be stored inside the arrays but I don't know where to put arrays. There will be an array for product numbers, an array for product name, and an array for price.
import java.io.*;
public class DataInsideArrays
{
public static DataInputStream a = new DataInputStream(System.in)
public static void main(String args[])throws Exception
{
int y = 0;
for(int x=1;x<=100;x++)
{
System.out.println("1 - Maintenance");
System.out.println("2 - Transaction");
System.out.println("");
System.out.print("Enter code: ");
int code =
Integer.parseInt(a.readLine());
System.out.println("");
if(code==l)
{
System.out.print("") ;
System.out.print("Product number: ");
System.out.print("Product name: ");
String prodname = a.readLine();
System.out.print("Price: ");
int price = Integer.parseInt(a.readLine());
System.out.println("");
}
else if(code==2)
{
System.out.println("Display List of Products-Prices")
System.out.print("Enter product number:
") ;
int prodnum
Integer.parseInt(a.readLine());
System.out.println("")
}
if(code==3)
{
System.out.println("Invalid");
System.out.println("Restart");
System.out.println("");
}}}}

First of all, where do you get this l (lowercase L) value in your for loop? Shouldn't this be 1 (number one)? Furthermore, it would be even better if it is 0 (zero) so you can use it as an index for your array.
Second thing, what's the point of int y = 0'? You are not using y anywhere in your program.
int y = 0;
for(int x = l; x <= 100; x++)
Change it to:
for(int x = 0; x < 100; x++)
Since you want to have 3 separate arrays, you should have 3 separate indexes to keep track of them.
Now let's see how to initialize an array to store the data. You should declare the size as a variable at the top of your class (or locally in your main()) to make it easier to change it later across your program. You can do the same with your array. Declare it inside your class or locally inside the main(). I will show you how to declare both outside of the class, but you should try it the other way too for practice.
Now remember, when using arrays you have to know the size of the array in advance as soon as you create it and you cannot change that size after. This means only that many elements can fit inside the array. If you want variable size structures, check out some of the answers with ArrayLists.
public class DataInsideArrays
{
public static DataInputStream a = new DataInputStream(System.in)
public static int size = 100; // now you only change this number and everything works
public static int[] productNumbers = new int[size];
public static String[] productNames = new String[size];
public static int[] productPrices = new int[size];
public static void main(String args[]) throws Exception
{
int prodnumIndex = 0; // index for tracking product numbers
int prodnameIndex = 0; // index for tracking product names
int prodpriceIndex = 0; // index for tracking product prices
for(int x = 0; x < size; x++)
{
// ... your code...
// ...
int prodNum = Integer.parseInt(a.readLine());
// check if we didn't reach our maximum size
if(prodnumIndex < productNumbers.length) {
productNumbers [prodnumIndex] = prodnum;
prodnumIndex++; // increment
} else {
System.out.println("Cannot add product number. Reached maximum amount.");
}
// ...
String prodName = a.readLine();
// check if we didn't reach our maximum size
if(prodnameIndex < productNames.length) {
productNames [prodnameIndex] = prodName ;
prodnameIndex++; // increment
} else {
System.out.println("Cannot add product name. Reached maximum amount.");
}
// ...
int prodPrice = Integer.parseInt(a.readLine());
// check if we didn't reach our maximum size
if(prodpriceIndex < productPrices.length) {
productPrices [prodpriceIndex] = prodPrice ;
prodpriceIndex++; // increment
} else {
System.out.println("Cannot add product number. Reached maximum amount.");
}
// ...
}
Another way you can achieve this is to create an object called Product that will contain the properties you need and then have an array of that object.
class Product {
int num;
String name;
int price;
Product(int num, String name, int price) {
this.num = num;
this.name = name;
this.price = price;
}
}
// ...
// declare your array of `Product` objects...
Product[] products = new Product[size];
// ...
// then you can do something like
System.out.println("Enter product number:");
int prodNum = Integer.parseInt(a.readLine());
System.out.println("Enter product name:");
String prodName = a.readLine();
System.out.println("Enter product price:");
int prodPrice = Integer.parseInt(a.readLine());
products[INDEX] = new Product(prodNum, prodName, prodPrice);
// ...
Also, consider using a double of a float for the product price since it is more realistic representation of actual products.

Do you have to use an array and "if" statements?
Common practice is to use a List as switch statement:
int[] productArray = new int[100];
List<Integer> productList = new ArrayList<Integer>();
for(int x=1;x<=100;x++) {
switch (code){
case 1:
productArray[x-1] = Integer.parseInt(a.readLine());
productList.add(new Integer(a.readLine()) );
break;
default:
System.out.println("Invalid")
break;
}
}

You should use a List instead of an array, because you don't know a priori the length for them.
A List allows you to dinamically add an element as soon as you got it, so you should "put the array" under the user input.
List<String> names = new ArrayList<String>(); //<-- do the same for price(Integer) and product number (Integer)
public static void main(String args[]) throws Exception) {
//...
if(code==1) //<-- This was a l, check again your code.
{
System.out.print("") ;
System.out.print("Product number: ");
System.out.print("Product name: ");
String prodname = a.readLine();
names.add(prodname); //<-- add value to ArrayList
System.out.print("Price: ");
int price = Integer.parselnt(a.readLine());
System.out.println("");
}
//...
}
To print the array content you just need to iterate over the ArrayList:
for(String prodname: names)
System.out.println(prodname); //<-- This will print all your product names

public class DataInsideArrays {
public static DataInputStream a = new DataInputStream(System.in);
List<String> productname=new ArrayList<String>();
public static void main(String args[]) throws Exception {
// rest of your code...
if(code == 1) {
System.out.print("") ;
System.out.print("Product number: ");
System.out.print("Product name: ");
String prodname = a.readLine();
System.out.print("Price: ");
int price = Integer.parseInt(a.readLine());
System.out.println("");
////////////////////////to store data place arraylist here/////////////////////////////
productname.add(prod);
///////////////////// //same way use arr to store price and product no
} else if(code == 2) {
System.out.println("Display List of Products-Prices") ;
System.out.print("Enter product number:") ;
int prodnum=Integer.parseInt(a.readLine());
System.out.println("");
}
if(code == 3) {
System.out.println("Invalid");
System.out.println("Restart");
System.out.println("");
}
}
}

Here's the correct codes for the output I want. Maybe is there any other way I can get the same output of this with different coding?
import java.io.*;
import java.util.ArrayList;
public class DataArrays
{
public static DataInputStream a = new DataInputStream(System.in);
public static void main(String args[])throws Exception
{
ArrayList<Integer> prodNum = new ArrayList<Integer>(100);
ArrayList<String> prodName = new ArrayList<String>(100);
ArrayList<Integer> prodPrice = new ArrayList<Integer>(100);
ArrayList<Integer> prodPay = new ArrayList<Integer>(100);
for(int x=1;x<=100;x++)
{
System.out.println("1 - Maintenance");
System.out.println("2 - Transaction");
System.out.println("");
System.out.print("Enter code: ");
int code = Integer.parseInt(a.readLine());
System.out.println("");
int y = 1;
if(code==1)
{
System.out.print("") ;
System.out.println("Product number: "+ x);
prodNum.add(x); //this brings 1st input to array element #0 which is not needed
prodNum.add(x);
System.out.print("Product name: ");
String prodname = a.readLine();
prodName.add(prodname); //this brings 1st input to array element #0 which is not needed
prodName.add(prodname);
System.out.print("Price: ");
int prodprice = Integer.parseInt(a.readLine());
prodPrice.add(prodprice); //this brings 1st input to array element #0 which is not needed
prodPrice.add(prodprice);
System.out.print("Payment: ");
int prodpay = Integer.parseInt(a.readLine());
prodPay.add(prodpay); //this brings 1st input to array element #0 which is not needed
prodPay.add(prodpay);
System.out.println("");
System.out.println("Start New Transaction:");
System.out.println("");
}
else if(code==2)
{
System.out.println("Display List of Products-Prices");
System.out.print("Enter product number: ");
int i = Integer.parseInt(a.readLine());
i = prodNum.get(i); //this gets the data stored in the arraylist. Assuming it starts with 1 and above
prodNum.set(1, i);
System.out.println("");
System.out.println("Product name: "+ prodName.get(i));
System.out.println("Product price: "+ prodPrice.get(i));
System.out.println("Product payment: "+ prodPay.get(i));
System.out.println("");
System.out.println("Start New Transaction:");
}
else if(code>=3)
{
System.out.println("Invalid");
System.out.println("Restart");
System.out.println("");
}
else if(code==0)
{
System.out.println("Program will end");
break;
}}}}
Thank for helping me guys. Really appreciated it.