I am trying to generate an arraylist in java by first inputting the default size desired of the said arraylist. Then I want to get the user to input the string to fill the arraylist. I have made one that almost works. The only problem is that for some reason I get a default value at the start.
For example, if I set the list length to 3 the list returned is: [,example,value,here]. I understand a value of 3 means 4 values in a list but I feel like that just doesn't look too nice. The problem I think lies in the way I set the size of the list but I don't see any other way.
When I set the list value manually in the for loop I don't get this problem. It only happens when I want the user to input the length. Where is the small error?
import java.util.*;
public class ListsPractice {
public static void main(String[] args) {
Scanner userin = new Scanner(System.in);
System.out.println("Enter length of desired list: ");
int lenlist = userin.nextInt();
ArrayList list1 = new ArrayList();
for(int counter = 0; counter <= lenlist; counter++) {
System.out.println("Enter an element: ");
String value=userin.nextLine();
list1.add(value);
}
System.out.println("the result is: "+list1.subList(1, lenlist+1));
}
}
Related
I am new to learning about parallel arrays and want to know how to effectively print content/elements using parallel array only, I tried but couldn't get it to work and function the way I want.
The task is: The program inputs an integer from the user representing how many peoples’ information will be entered. Then, the program inputs the information one person at a time (name first, then age), storing this information in two related arrays.
Next, the program inputs an integer representing the person on the list whose information should be displayed (to get information for the first person, the user would enter ‘1’). The program makes a statement about the person’s name and age.
Although I got the name and age to work until the integer the user inputs, but after that I am not sure how to do
Sample input:
4
Vince
5
Alexina
8
Ahmed
4
Jorge
2
2 // I am confused about this part, how would I make it so that it prints the desired name,
//for example with this input, it should print:
Sample output:
Alexina is 8 years old
My code:
import java.util.Scanner;
class Example {
public static void main (String[] args) {
Scanner keyboard = new Scanner(System.in);
int[] numbers = new int[keyboard.nextInt()];
for (int x = 0; x < num.length; x++){
String[] name = {keyboard.next()};
int[] age = {keyboard.nextInt()};
}
int num2 = keyboard.nextInt();
System.out.println(); // what would I say here?
}
}
You need to rewrite your code so your arrays aren't being assigned within the loop. You want to add values to the arrays, not reset them each time, and you want to be able to access them afterwards. Below is a modified version of your code:
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
int num = keyboard.nextInt();
keyboard.nextLine(); //you also need to consume the newline character(s)
String[] name = new String[num]; //declare the arrays outside the loop
int[] age = new int[num];
for (int x = 0; x < num; x++){
name[x] = keyboard.nextLine(); //add a value instead of resetting the array
age[x] = keyboard.nextInt();
keyboard.nextLine(); //again, consume the newline character(s) every time you call nextInt()
}
int num2 = keyboard.nextInt() - 1; //subtract one (array indices start at 0)
System.out.println(name[num2] + " is " + age[num2] + " years old"); //construct your string with your now-visible arrays
}
As I think you have to think about the local and global variable usage in java.In brief,
Local variables can only use within the method or block, Local variable is available only to method or block in which it is declared.
For example:
{
int y[]=new Int[4];
}
this y array can be accessed within the block only.
Global Variable has to be declared anywhere in the class body but not inside any method or block. If a variable is declared as global, it can be used anywhere in the class.
In your code you try to create arrays and use them out of the For loop. But your arrays are valid only inside the For loop. After every loop runs all info is lost.there will be new array creation for every iteration of For loop.
therefore, In order to access and save the information you have to declare your arrays before the For loop and access and store data using iteration number as the index. finally, to print the data you gathered, you have to scan new input as integer variable.then you can access your arrays as you wanted.
//For example
int [] age=new int[4]; //global -Can access inside or outside the For loop
int[] numbers = new int[keyboard.nextInt()];
for (int x = 0; x < 4; x++){
age[x] = keyboard.nextInt(); //Local
}
int num2 = keyboard.nextInt();
System.out.println(age[num2]); // Here you have to access global arrays using num2 num2
}
}
I am new to JAVA and this is what I have to do:
Accept a set of marks (out of 100). The user should press the Enter button after each mark is entered and the mark should then be added to an ArrayList of Integers.
This is what I have so far:
int score = Integer.parseInt(marksinput.getText());
ArrayList<Integer> marks = new ArrayList();
Collections.addAll(marks, score);
String out = "";
String Out = null;
int[] studentmarks = {score};
for (int item : studentmarks) {
marksoutput.setText(""+item);
}
if (score > 100) {
marksoutput.setText("Enter marks\n out of 100");
}
This only adds one mark in the arraylist and I need user to input as many marks he wants. I know that my arraylist is wrong, which is why it only takes 1 number but I do not know how to make all the input numbers go in arraylist. What I have is that it takes the number and if user inputs another number, it just replaces the older number. I want it to display both the numbers not just one. Any help is appreciated and thank you in advance!☻☻
(This is not a duplicate even though others have the same title)
In case what you are after is a program that adds any integer typed by the user into an ArrayList, what you would have to do is the following:
Scanner scanner = new Scanner(System.in);
List<Integer> ints = new ArrayList<Integer>();
while(true)
ints.add(scanner.nextInt());
What this program will do, is let the user input any number and automatically puts it into an ArrayList for the user. These integers can then be accessed by using the get method from the ArrayList, like so:
ints.get(0);
Where the zero in the above code sample, indicates the index in the ArrayList from where you would like to retrieve an integer.
Since this website is not there to help people write entire programs, this is the very basics of the ArrayList I have given you.
The ArrayList is a subclass of List, which is why we can define the variable using List. The while loop in the above example will keep on going forever unless you add some logic to it. Should you want it to end after executing a certain amount of times, I would recommend using a for loop rather than a while loop.
Best regards,
Since it seems you are really new,
What you are looking for is a for-loop
From the Java documentation, he is the syntax of a for-loop in Java
for (initialization; termination; increment) {
statement(s)
}
Initialization: Obviously you want to start from 0
Termination: you want to stop after 100 inputs, so that's 99 (starting from zero)
Increment: you want to "count" one by one so count++
for(int counter = 0; counter < 100; counter++) {
//Ask user for input
//read and add to the ArrayList
}
So before you enter the for-loop you need to initialize the ArrayList, and a Scanner to read input:
Scanner sc = new Scanner(System.in);
ArrayList<Integer> list = new ArrayList();
for(int counter=0; counter < 100; counter++) {
System.out.println("please enter the " + counter + " number");
int x = sc.nextInt();
list.add(x);
}
I have an issue for creating an array based on the total amount of numbers entered into the array.
Essentially the program is expected to work as the following: the user is prompted for n numbers to enter into an array. So until the user types '000' as their input, the user will be prompted for a new number.
Note: for this array, I do not want the user to input the amount of numbers they want to enter for the array size. Instead, I want the user to continue inputting random numbers until '000' has been inputted, then, the total amount of numbers that has been entered into the array, is the size of such array.
For example: this would work if we have int array[] = {1, 2, 4, 6}, this will automatically set array size to 4, without actually explicitly declaring the array size as 4 elements. Similarly, with my code, I want it where the numbers that the user enters is added to the array, and then the array size is automatically given from the amount of numbers the user has entered like above.
It is important to note that we do not know the length of the array until the user has entered all n numbers.
I have attempted a skeleton, but it returns a cannot find symbol error:
Code:
//Array Code
import java.util.*;
class setArray {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int stopInput = 000;
int number;
System.out.print("Enter a number: ");
number = input.nextInt();
while(number != stopInput) {
System.out.print("Enter a number: ");
number = input.nextInt();
int array[] = {number};
}
System.out.print("Array size: " + array.length);
} // Main brace
} // Class brace
setArray.java:19: error: cannot find symbol
System.out.print("Array Size: " + array.length);
symbol: variable array
location: class setArray
1 error
You have a few errors here. The first is understanding why you get your immediate error. The variable array is declared within the scope of the while loop. It can not be seen outside of this loop. That is why the compiler is complaining.
The second is that the size of the array (if declared outside of the loop) will always be 1. From my understanding of what you have written as an attempt to solve the problem you have describe shows that you are not tackling the problem correctly.
While you don't known the the final length of the array to be entered; you do need to store the values entered (my inference) to populate the final array. To store the value entered by the user you need a list that will grow with the input.
List<Integer> values = new ArrayList<>();
while (number != stopInput) {
System.out.print("Enter a number: ");
values.add(Integer.valueOf(input.nextInt()));
}
Integer[] array = values.toArray(new Integer[values.size()]);
Firstly, the compilation error is because the array variable is not visible from the System.out.println line. This is because it's declared inside the while loop, so is only visible inside the while loop.
To make it visible to the whole method, declare it before the while loop.
Secondly, arrays cannot be resized. You declare an array to be a certain size, and you cannot add or remove elements.
My suggestion would be to use an ArrayList. Declare one before your loop, and add the new number inside the loop. After the loop, the size should be how many numbers were entered.
Finally, there's no difference between 000 and 0. Is 0 a valid input number?
You can use
List<Integer> array=new ArrayList<Integer>();
while(number != stopInput) {
System.out.print("Enter a number: ");
number = input.nextInt();
array.add(number);
}
This sounds like a job for java.util.ArrayList - this is the array that doesn't have a fixed size and is growing as you add values to it automatically under the covers.
The error is caused because you are creating the array only within the scope of the while loop. You need to create it outside the loop. Secondly, standard arrays are not dynamic, so you would need to either set the size and increase it as needed, or just simply use an ArrayList.
Psuedo:
ArrayList<Integer> list = new ArrayList<Integer>()
...
while(not stop number)
list.add(number)
...
print(list.size())
If you really want to use an Array, here is how you can do it
public static void main(String[] args){
STOP_ENTRY = "000";
scan = new Scanner(System.in);
entry = "";
while(true){
System.out.print("Enter #: ");
String tempS = scan.nextLine();
if(tempS.equals(STOP_ENTRY)) break;
else entry += tempS + ":";
}
String[] split = entry.split(":");
int[] intArray = new int[split.length];
System.out.println("Length of created intArray = " + intArray.length); //length of created array
for(int i = 0; i < intArray.length; i++){
intArray[i] = Integer.parseInt(split[i]);
System.out.println("intArray[" + i + "] => " + String.valueOf(intArray[i]));
}
}
I would recommend an ArrayList, as it dynamically changes is size when you add an element, but do whatever you'd like.
An important note, this does not handle any malicious entry that you might not want (characters, symbols), and will error if they are entered, something you can easily add if you need
I am making a program that prompts the user for 3 integers and prints out the biggest one chosen. I am stuck with 2 problems at the moment. I would like to know how I can make the program so that the user can only choose integers from the array. I would also like to know how to find and print out the biggest integer from the ones that the user chose. I'm quite new to programming so all feedback is appreciated.
Thanks!
import java.util.Scanner;
public class Lab14C // name of class file
{
public static void main(String [] args)
{
int[] array = {0,1,2,3,4,5,6,7,8,9};
for(int i=0; i<array.length; i++)
{
System.out.print(array[i] + " ");
}
System.out.println("\n");
Scanner array1 = new Scanner(System.in);
System.out.println("What is your first integer? ");
double array11 = array1.nextInt();
Scanner array2 = new Scanner(System.in);
System.out.println("What is your second integer? ");
double array22 = array2.nextInt();
Scanner array3 = new Scanner(System.in);
System.out.println("What is your third integer? ");
double array33 = array3.nextInt();
System.out.println("\n");
}
}
I don't think there is a way to force a user to input an element. Few things you could do is :
Tell the user he has to select a number in a particular range.
Keep the input statement in a loop. If the entered element exists in array , go ahead. Else tell the user to enter again.
Printing the biggest integer can be done using Math.max(double,double) function. For three elements you can try System.out.println("Max of three is "+Math.max(array11,Math.max(array22,array33)))
You can do it yourself if you want instead of built in function like:
if(array1>array2&&array1>array3)
//print max as array1
else if(array2>array1&&array2>array3)
//print max as array2
else //print array3 as max
Also change your element types to int as you are reading integer.
1) There is no need to create a new Scanner all the time.
Just create one Scanner (which I would just call input or scanner or something that makes sense).
2) If you're reading int's why are you storing them in doubles?
3) To check for a certain condition you use if(*condition*) { /*do something */ }. So if you want to check if x is smaller than y you do if(x < y) { /* do something */ }. (In your case you'll want to check if current input is greater than biggest input and if so set the biggest input to current input.)
4) For a sorted array you can use Arrays.binarySearch(array, elementToSearch) which will return the index of the element when found, or a negative number if not found (the negative number is (-(insertionPoint)-1)). (So you can check if the number entered by the user is in the array and keep asking for a new number if is not.)
1) How I can make the program so that the user can only choose integers from the array.?
You are declaring array variable as int[] so it stores only integer values. Whenever you retrives the value from this array, it returns int value only so you don't have to worry about it.
2)how to find and print out the biggest integer from the ones that the user chose.?
To find the maximum or minimum from a set of values, Java provide a function name Math#max(). You can use it like this :
int maxValue = Math.max(Math.max(array11,array22),array33);
Here is the doc for Math library.
I need to check the array to see if the user input is already present, and display a message as to whether it is or isn't there. The first part is working, but I tried to create a method for the word check, and I'm not sure if I'm on the right path or not, cheers.
import java.util.Scanner;
public class InputLoop {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String array[] = new String[10];
int num = array.length, i = 0;
System.out.println("Enter a word");
for (i = 0; i < num; i++) {
while (scan.hasNextInt()) // while non-integers are present...
{
scan.next(); // ...read and discard input, then prompt again
System.out.println("Bad input. Enter a word");
}
array[i] = scan.next();
WordCheck();
}
}
public void WordCheck(String[] i) {
Scanner scan = new Scanner(System.in);
System.out.println("Enter another word");
if (scan.next().equals(array[i])) {
System.out.println("The word has been found");
} else {
System.out.println("The word has not been found");
}
}
}
Right. You've clearly gone down a bad thought process, so let's just clear the slate and have a re-think.
Step one: You want to take some user input
Step two: Compare it with all previous user inputs to see if it's present.
If it is present, return a message indicating that value has been inputted.
otherwise ignore the input and continue execution
Repeat step one.
The solution
So, let's review what you've got, and how you need to change it.
public static void main(String[] args)
If I were you, I would avoid calling methods directly from here. If you do, every method will need to be static, which is a pointless adjustment in scope for the functionality of your class. Create a new instance of your class, inside the main method, and move this code to the class' constructor. This will remove the need to make every single method static.
Scanner scan = new Scanner(System.in);
String array[] = new String[10];
Okay, so you've created a scanner object that takes input from the System.in stream. That's a reasonable thing to do when taking input from the keyboard. You've also created an array to contain each item. If you only want the user to be able to type in 10 values, then this is fine. Personally, I would use an ArrayList, because it means you can take in as many user inputs as the user desires.
Secondly, you want a function to compare the input, with all other inputs. What you have at the moment clearly isn't working, so let's have another go at it.
You will need some input, userInput, and a collection to compare it against, allInputs.
allInputs needs to be accessible from any point in the program, so it's probably wise to make it into a field, rather than a local variable.
Then, because you're comparing userInput against all values, you're going to need a foreach loop:
for(String s : allInputs)
{
if(s.equals(userInput))
{
// Output message code.
}
}
Now the trick is fitting this inside a loop that works with this program. That is up to you.
One simple solution is to use a Set:
Set<String> words = new HashSet<String>();
Add words with the add() method and check if a word is already added with contains(word) method.
EDIT
If you must use Arrays you can keep the array sorted and do a binary search:
Arrays.sort(words);
boolean isAlreadyAdded = Arrays.binarySearch(words, newWord) >= 0;
You're going to have to loop through the entire array and check if scan.next() equals any of them - if so return true - as such:
String toCheck = scan.next();
for (String string : i) { //For each String (string) in i
if (toCheck.equals(i)) {
System.out.println("The word has been found");
return;
}
}
System.out.println("The word has not been found");
This supposes you call WordCheck(), passing the array to it - this method also has to be static for you to call it from the main() method.
You can use the arraylist.contains("name") method to check if there is a duplicate user entry.