Why Can't Populate Array Of Objects From Inside Constructor
Feb 21, 2015
The experiments will slowly converge towards one big experiment: a simple game. I have just a little interest in games (perhaps I should have more), but making one - even a simple one - should be self rewarding.
However, now to the point.
* The experiment creates an array of rectangle objects.
* The rectangles are painted inside a Frame object at random x,y coords generated by a random number generator
* The rectangles are stationary.
* The rectangles are each assigned their own random colour.
* The array of rectangle objects is created inside the constructor of the class.
The actual code contains various other variables and methods which would distract from a quick analysis, so below is code which has the same logical structure which also fails (instead of array of rectangles, I have used arrays of integers).
import java.util.Random;
/**
* Experiment 14 - see if it works simply - (with integer arrays)
*/
public class TestingArrays {
// instance variables
int N = 10; // the size of the array - 10 elements
int[] a;
import java.io.*; import java.util.Scanner; public class asciiFile { int height; int width; Scanner input; char[][] poop; public asciiFile(File f) throws FileNotFoundException{ //constructor
[code]...
The constructor is supposed to take an ASCII file, take the numbers in the file, and populate a 2D array with the numbers in the file.
For some reason, the for loop I use to populate the array works outside of the constructor. When I put it in one of the methods, it runs normally. However, when I keep it in the constructor, I get the following error:
Exception in thread "main" java.lang.NullPointerException
I want to create a simple app that takes a name from the console then compares the name to a small phone book,when the name matches another name it will return the associated phone number.
I have a small contacts class which has name and number fields,Then I have a phone book class which populates an array with 4 contact objects that I can compare the entered number against.
here is my contacts class
public class Contact { String name; int number;
[Code].....
In the main method I am just trying to print out one of the fields for one contact to see if I can actually access it to compare it to the name entered.Its saying "MaryJones" cannot be resolved to a type.I'm guessing I cant create all that code in the constructor?
1 - I don't understand why I'm getting an empty stack error when calling the removecard method in my Table class line 13?
2 - I am trying to use a constructor to populate my deck of cards instead of a method when creating my theDeck object in my Table class line 11 but I get the following error:
java.lang.StackOverflowError at java.util.Vector.<init>(Unknown Source) at java.util.Vector.<init>(Unknown Source) at java.util.Stack.<init>(Unknown Source) at Deck.<init>(Deck.java:7) at Deck.<init>(Deck.java:34)
We were given a class lab that asks us to write a program that create a multidimensional array ( 5 x 5 ), populates the array using nested loops with letter from A until Y, and displays the array to the screen. and the result should look like this:
A B C D E F G H I J K L M N O P Q R S T U V W X Y
How to write this program.. I have tried all my best but the results are not coming like this..
class GenericQueue<E> { private LinkedList<E> list = new LinkedList<E>(); public void push(E element) { list.addFirst(element); } public E pull() { return list.removeLast();
[code]...
Is a constructor required to create an object, if one of its instance or class variables haven't been instantiated? Like private String string;
I am developing a java based software connected with a mysql database. I have an Item table in my database. I created a bean class which can keep all item data with it and. Then I loaded each Item data in to its object and fill a Jcombobox. Now I want to search with Item name and get all Item data when selecting that item. I have overidden the toString method to Item name in that class. Is there any way to search my Item objects inside a jcombobox?
I am trying to place a number of JLabel and JTextField objects inside a JPanel which has a JScrollPane.
One thing is, that at one time, I have have a certain number of JLabel and JTextField objects which number would cover an area greater than the JPanel's vertical size.
How when I implement the JScrollPane and I run the program, the scroll bars appear, but they don't scroll the pane inside the JPanel, the items are fixed.
Could the problem be because I am using a Null Layout.
Will I have to use one of the standard layouts available, like GridLayout for the JScrollPane scrolling function to work?
I have this working manually, but need creating this from a DB Connection and populating the Array with the results. I just need populating "DestinationItem[]" from the SQL below
DestinationBean.java // Manual Array works but I need this to be populated from DB using the below Query and DB Connection info. private DestinationItem[] destinationResults = new DestinationItem[]{ new DestinationItem("58285", "Dodge Grand Caravan"), new DestinationItem("57605", "Dodge SX 2.0"), new DestinationItem("58265", "Chrysler 300 Touring")
Still trying to get a handle on arrays! So, I declare an array to be a 46x1 and I am trying to populate it with a Log formula that I am using but I keep getting an ArrayIndexOutofBoundsException.
Code :
private double[][] LNValues = new double[46][1]; //Calculating y=LN(E-k) and Initializing the Array for(int x=0; x<LNValues.length; x++) { double i = Math.log(eValues[x][1] - kValue); if(i > 0)
why I need to populate an array with leading zeros. It sounds like it wants me to populate the entire array for one number (string). When I use next(), it separates the numbers so why do I need to go the leading zeros route?
This assignment will give you practice with external input files and arrays. You are going to write a program that adds together large integers. The built-in type int has a maximum value of 2,147,483,647. Anything larger will cause what is known as overflow. Java also has a type called long that has a larger range, but even values of type long can be at most 9,223,372,036,854,775,807.The approach you are to implement is to store each integer in an array of digits, with one digit per array element. We will be using arrays of length 50, so we will be able to store integers up to 50 digits long. We have to be careful in how we store these digits. Consider, for example, storing the numbers 38423 and 27. If we store these at the front of the array with the leading digit of each number in index 0 of the array, then when we go to add these numbers together, we're likely to add them like this:
38423 27
To simulate this right-shifting of values, we will store each value as a sequence of exactly 50 digits, but we'll allow the number to have leading 0's. For example, the problem above is converted into:
Now the columns line up properly and we have plenty of space at the front in case we have even longer numbers to add to these.The data for your program will be stored in a file called sum.txt. Each line of the input file will have a different addition problem for you to solve. Each line will have one or more integers to be added together. Take a look at the input file at the end of this write-up and the output you are supposed to produce. Notice that you produce a line of output for each input line showing the addition problem you are solving and its answer. Your output should also indicate at the end how many lines of input were processed. You must exactly reproduce this output.
You should use the techniques described in chapter 6 to open a file, to read it line by line, and to process the contents of each line. In reading these numbers, you wont be able to read them as ints or longs because many of them are too large to be stored in an int or long. So youll have to read them as String values using calls on the method next(). Your first task, then, will be to convert a String of digits into an array of 50 digits. As described above, youll want to shift the number to the right and include leading 0s in front.
The String method charAt and the method Character.getNumericValue will be useful for solving this part of the problem.You are to add up each line of numbers, which means that youll have to write some code that allows you to add together two of these numbers or to add one of them to another. This is something you learned in Elementary School to add starting from the right, keeping track of whether there is a digit to carry from one column to the next. Your challenge here is to take a process that you are familiar with and to write code that performs the corresponding task.
Your program also must write out these numbers. In doing so, it should not print any leading 0s. Even though it is convenient to store the number internally with leading 0s, a person reading your output would rather see these numbers without any leading 0s.You can assume that the input file has numbers that have 50 or fewer digits and that the answer is always 50 digits or fewer. Notice, however, that you have to deal with the possibility that an individual number might be 0 or the answer might be 0. There will be no negative integers in the input file.You should solve this problem using arrays that are exactly 50 digits long. Certain bugs can be solved by stretching the array to something like 51 digits, but it shouldnt be necessary to do that and you would lose style points if your arrays require more than 50 digits.The choice of 50 for the number of digits is arbitrary (a magic number), so you should introduce a class constant that you use throughout that would make it easy to modify your code to operate with a different number of digits.
Consider the input file as an example of the kind of problems your program must solve. We might use a more complex input file for actual grading. The Java class libraries include classes called BigInteger and BigDecimal that use a strategy similar to what we are asking you to implement in this program. You are not allowed to solve this problem using BigInteger or BigDecimal. You must solve it using arrays of digits.Your program should be stored in a file called Sum.java.
I have a simple txt file, each line simply containing 1 word.I would like each work to represent an index of the array..im having some difficulty populating an array from either a txt file or a scanner.i seem to be able to fill the scanner so to speak with the contents of the text file but not the array. I don't know how to syntax it
import java.io.File; import java.io.FileNotFoundException; import java.util.Scanner; import java.util.Arrays; public class ReadFile public static void main(String[] args) {
Write a program that creates an array that can hold 9 double values that represent baseball batting averages for a starting baseball lineup. Use a for loop to populate array with random double values in the range of 0.00 to 0.500. Recall that "double" values are what Java calls "real" numbers. Use a second for loop to print the values in the array with one number per line. Finally, use a third for loop to traverse the array and find and print the maximum batting average in the array. Note: you will need to use String.format to control the precision of a double number when you print it- Here is my code so far:
public class P2F { public static void main (String[] args) { double [] player= new double [9]; //player[0]= Math.random(); for (int index=0; index < player.length; index++) {
[Code] ....
When I open the terminal window I get different variations of this [D@4545c5]. I would like to know all the things I am doing wrong.
I must fill a 2d array randomly and then apply methods to the array. However i keep getting an out of bounds exception no matter what dimensions i use. I have a test and a class program.
import java.util.*; import java.lang.Math; import java.util.Arrays; import java.util.Random; class SummerStats { Random rand = new Random();
I am working in NetBeans and I am receiving numerous error messages with my code "not suitable constructor for lineItem.
import java.util.ArrayList; public class Transaction { private final ArrayList<LineItem> lineItems; private int customerID; private String customerName; private String LineItem; private int i;
[Code] .....
Specific Requirements for the Transaction Class :
1. The Transaction class should have a constructor with two parameters. The first is an integer containing the customer's ID and the second is a String containing the customer's name.
2. There should be a method to allow the addition of a line item to the transcript. The three parameters for the addLineItem method will be (1) the item name, (2) the quantity, and (3) the single item price.
3. There should be a method to allow the updating of a line item already in the transaction. Notice that updating an item means changing the quantity or price (or both). The parameters for the updateItem method are also (1) the item name, (2) the quantity, and (3) the single item price.
Notice that the updating of a specific line item requires a search through the ArrayList to find the desired item. Anytime a search is done, the possibility exists that the search will be unsuccessful. It is often difficult to decide what action should be taken when such an "exception" occurs. Since exception handling is not covered until later in this textbook, make some arbitrary decisions for this project. If the item to be updated is not found, take the simplest action possible and do nothing. Do not print an error message to the screen. Simply leave the transaction unchanged.
4. The transaction class needs a method called getTotalPrice to return the total price of the transaction.
5. There should also be a method to return information about a specific line item. It should return a single String object in the same format described for the LineItem class:
Colgate Toothpaste qty 2 @ $2.99 $5.98
Again, the possibility exists that the search for a specific line item will fail. In this instance, you should return a string containing a message similar to this:
Colgate Toothpaste not found.
6. The final method needed is a toString method. It should return the transaction information in a single String object. It should use the following format:
"on each step of the loop you can calculate an entire year as opposed to a single month, otherwise you can calculate monthly, but instead of printing, create an array and fill it up with your solutions, then have a second loop where you add them up by dozens to print yearly values, alternatively, have a counter k that adds up to 12, and two variables for adding up the monthly results, increment these after you calculate the monthly value, and whenever k hits 12, print them and reset to zero. print a final time once you leave the loop. "
int year = loanDurationYears-14; int[] years= new int[loanDurationYears]; periods = loanDurationYears*12; for(int i=0;i<1;i++) { for(year = 0;year<loanDurationYears;year++) { years[year] = year+1;
So I want to write a constructor that creates a new object with the data from the array values. I don't know where to start. It's the last method in the code:
public class Measurements { private double[] values; private double[] newArray; private int n; //numberofvalues private double[] ms; public Measurements(int max) { //constructor
I've a vertical-bar-delimited file where most elements contain text, some contain whitespace, and some are empty. Examples:
62RG|fe|Pencil Financial Group, LLC||doug@pencil.com|||85637889|Cross, Ben|bcross@godaddy.net|Bernard|Cross|Ben||315 One Tree Hill Terrace|Lafayette|LA
String str_arry = innline.split( "|", 17); lisst.add( new Contact( str_arry));
and my Contact class has the constructor
public Contact( String[] str_arry) { for( int ii = 0 ; ii < str_arry.length ; ii++ ) { if( str_arry[ii].matches("^s+$")) { str_arry[ii] = null; System.out.println("hit a null");
[Code]...
I expect the for-loop in the constructor to find any elements containing whitespace characters and set them to null for subsequent assignment.And when the code runs I do see some hit-statements pop up, so the detecting part is working.
But when I then process the list and access a Contact object and test fields for nulls I don't find any ie
if( aContactObj.getfFCity() == null) System.out.println("city is null");
never prints when it should.
What's the trick? Or is my approach wrong and if so what should it be?
I have an assignment on sorting, i kno i can get the sorting down but im having an issue with inputing the 512 ints in a file into an array. the instructor provided us with a file with 4 equal sets of ints. i tried to make my array of size [scan.nextInt()] and it cuts off the last 21 ints. and skips the first int. how can i get all of the integers in the text file into my array? this is what i have so far. if i hard code the array to size 50000 and then try to print the array it compiles but errors out when running it.
System.out.println("Please Enter text file in this format, XXXXX.txt :"); String file =fileName.nextLine(); Scanner scan = new Scanner(new File(file)); int [] data = new int[scan.nextInt()]; <-------here it skips first int int count= data.length; for (int i=0; i<data.length-1;i++) { data[i]=scan.nextInt(); } System.out.print(Arrays.toString(data));
rst 4 ints in output are: 501, 257, 390, 478...., supposed to be 492,501,390....and last ints are: ....88, 83, 79, 0 and supposed to be :88 83 79 77 76 72 71 71 66 57 56 48 48 41 33 30 23 23 18 17 15 13 9....it replace last ints with 0. why ? and how do i fix this. attached it the text file
Exercise the Coin class using a driver class in which 5 coins are flipped, as a group, 1024 times. Display the number of times exactly 4 tails are obtained. Display the number of times exactly 5 tails are obtained. Use an array of Coin.
how to put an object into an array?I know how to make a coin class with a Heads and Tails, but I dont know how to make 5 coins all at once.
I know the first line below creates an object but the second line creates an array of cars, I'm just not sure how it does that. I can see sportsCar is one object in the array but the others are written in a different way. It seems there should a couple names there instead. Please explain the syntax in this code that's highlighted. I don't know how to make sense of it and I've read through the book where I got it where it explained creating objects.
Auto sportsCar = new Auto("Ferrari", 0, 0.0); Auto [] cars = {new auto("BMW", 100, 15.0), sportsCar, new Auto()};
I have a list of objects in my bean (ex: List<Apple> applies = new ArrayList<Apple>() ).The object has several fields (ex: supplier, color, width, height, breadth, etc.)I want to show this list on the front end. However I also want to allow the user to edit the attributes of the apples.So from the front end I will have like a list of fields where a set of fields is related to a single object in the list.I would also like to add/delete apples.
What first came to my mind is to map every field in the object Apple to a List. For example if Apple has field suppliers and field color then in the bean I would create two Lists, List<String> supplier, and List<String> color.From the front end I would display the contents of these Lists rather then the List<Apple> apples.T
he name of the field would be the same for each set of attributes.On save (form submit) the Lists would be re-populated with the field values (changed or not) and then I would be my Apple objects from the bean before saving in database.However I am not sure if there is something in JSF that can achieve this in a simple way, working only with List<Apple> rather than adding additional Lists.
