Printing out a 2d character array is not difficult, but the way I need to do it seems to be.
My current goal is initialize a 2d character array, such that every cell contains '-'. This must be done within the constructor method. Below is what I have thus far.
public class GameOfLife {
public final int MAX_SIZE = 12;
// instance variables
private char [][] current = new char[MAX_SIZE][MAX_SIZE];
private char [][] next = new char[MAX_SIZE][MAX_SIZE];
Scanner keyboard = new Scanner(System.in);
/**
* Constructor for objects of class GameOfLife.
* Initializes the current array to '-'.
*/
public void GameOfLife() {
for ( int i = 0; i < MAX_SIZE; i++){
for ( int j = 0; j < MAX_SIZE; j++){
current [i][j] = '-';
}
}
#Override public String toString() {
StringBuilder sb = new StringBuilder();
for ( int i = 0; i < MAX_SIZE; i++){
for ( int j = 0; j < MAX_SIZE; j++){
sb.append(current[i][j]);
sb.append(" ");
}
sb.append("\n"); // add new line
}
return sb.toString(); // convert to String and return
}
}`
I know how to properly print it if it were just to be printed within this method; however, I must use the "GameOfLife" constructor in the following way. This next code is in the driver class, which is called "gameoflifedriver".
// Create a GameOfLife object
GameOfLife lifeGame = new GameOfLife();
System.out.print(lifeGame);
The problem that I am having is that the lifeGame will not print, and an odd error message occurs - GameOfLife#5d3892b3. I know there are ways to print it, but I cannot change any of the code in the driver class - so all of the edits must be in the GameOfLife code. Any thoughts?
You can override the toString() method. Also you could use a StringBuilder:
#Override
public String toString() {
StringBuilder sb = new StringBuilder();
for ( int i = 0; i < MAX_SIZE; i++){
for ( int j = 0; j < MAX_SIZE; j++){
sb.append(current[i][j]);
sb.append(" ");
}
sb.append("\n"); // add new line
}
return sb.toString(); // convert to String and return
}
Then you can print this representation with:
GameOfLife lifeGame = new GameOfLife();
System.out.print(lifeGame);
Note: Constructors don't have a return type, so you shouldn't declare it with return type void:
public GameOfLife() {/* Constructor body */}
The Class GameOfLife constructor should not have void return type (java rule).
And the toString() method is good to implement.
Related
i hope someone can help me, i have the following problem.
I have a variable that looks like this:
var a = "01VENT000KRV010WFEVVV055";
I would like to either:
have the last 3 figures of the variable (e.g. 055) as an int
or remove ALL non-figures out of the variable (e.g. 01000010055) as an int
My idea was that:
int sub = Integer.parseInt(a.substring(a.length-3));
or:
int sub = Integer.parseInt(a.replaceAll("[\\D]", ""));
That didnt work, so i would really appreciate if someone could help me here
Thanks
Note all methods can potentially return an empty string.
public static void main(String[] args) {
// TODO code application logic here
String a = "01VENT000KRV010WFEVVV055";
System.out.println(removeChars(a));
System.out.println(removeDigits(a));
System.out.println(getLastThreeChars(a));
}
//This method removes Characters from a string and returns a String of numbers
static String removeChars(String t)
{
String tempString = "";
for(int i = 0; i < t.length(); i++)
{
if(Character.isDigit(t.charAt(i)))
{
tempString += t.charAt(i);
}
}
return tempString;
}
//This method removes Digits from a string and returns only characters
static String removeDigits(String t)
{
String tempString = "";
for(int i = 0; i < t.length(); i++)
{
if(Character.isAlphabetic(t.charAt(i)))
{
tempString += t.charAt(i);
}
}
return tempString;
}
//This methods prints the last 3 char of a string
static String getLastThreeChars(String t)
{
StringBuilder tempString = new StringBuilder();
for(int i = t.length() - 1; i > t.length() - 1 - 3; i--)
{
tempString.append(t.charAt(i));
}
return tempString.reverse().toString();
}
I am trying to keep the values of my array dates from the Unsorted method, so that it can be used to have another return value in a separate method, that being the Sorted method. I know there would be no trouble in this, but when running the program (which is done using a GUI) the array outside of the Unsorted method is only 1 item long, effectively losing all but one of its items.
I have reason to believe that this is because of the line
while((line = myFile.readLine()) != null){ ...
Because when i try to output the items of the array outside of the while loop in the Sorted function, it also returns only the last item of the array. There is no reason to use split.string here, as I know the Tokenizer will get the job done easily, and the project calls for using the Tokenizer. I would imagine that I could change the way the tokens are added to the array, but I have tried the add function, and it did not work, and when doing so I get "The Method add(String) is undefined for type string"
Here is the example text file(dates.txt):
20161001
20080912,20131120,19980927
20020202,hello
20120104
These dates are structured "yearmonthday" all with a length of 8. the hello is added to ensure that we check for the appropriate items in the text file.
Here is the code:
import java.util.StringTokenizer;
public class Project1{
public static TextFileInput myFile;
public static StringTokenizer myTokens;
public static String[] dates;
public static String line;
public String Unsorted(String date) {
myFile = new TextFileInput("dates.txt");
while((line = myFile.readLine()) != null){
myTokens = new StringTokenizer(line,",");
dates = new String[myTokens.countTokens()];
int i=0;
while (myTokens.hasMoreTokens()) {
dates[i]=myTokens.nextToken();
i++;
}
// prints any items that are not 8 chars long
for (int j = 0; j < dates.length; j++){
if (dates[j].length() < 8){
System.out.println(dates[j]);
}
}
// I changed the date += String.valueof.dates[i] + "/n"
// to System.out.println
for (int n = 0; n < dates.length; n++){
if (dates[n].length() == 8){
System.out.println(dates[n]);
}
}
}
return date;
}
// I changed the datesort += String.valueof.dates[i] + "/n"
// to System.out.println
public String Sorted(String datesort){
selectionSort(dates, dates.length);
for (int i = 0; i < dates.length; i++){
if (dates[i].length() == 8){
System.out.println(dates[i]);
}
}
return datesort;
}
private static void selectionSort(String array[], int length) {
for ( int i = 0; i < length - 1; i++ ) {
int indexLowest = i;
for ( int j = i + 1; j < length; j++ )
if ( array[j].compareTo(array[indexLowest]) < 0)
indexLowest = j;
if ( array[indexLowest] != array[i] ) {
String temp = array[indexLowest];
array[indexLowest] = array[i];
array[i] = temp;
}
}
}
}
The out of this program is :
hello
20161001
20080912
20131120
19980927
20020202
20120104
20120104
Yet it should be:
hello
20161001
20080912
20131120
19980927
20020202
20120104
19980927
20020202
20080912
20120104
20131120
20161001
thanks ahead of time, I apologize if I was unclear at all.
New to java programming and I am currently trying to create a class similar to ArrayList using Arrays.
Am trying to add elements to an array and expand the array by copying them to a new array of bigger size.
I am getting an out of index error at 20.
Code may be messy but currently really stuck.
public class MyArrayList{
private String[] strings;
private int arraySize;
private int storedStrings;
public MyArrayList(int arraySize){
this.arraySize = arraySize;
this.strings = new String[arraySize];
}
public void addString(String string){
storedStrings = 0;
for (int i = 0; i < this.arraySize;i ++){
if (strings[i] != null){
storedStrings = storedStrings +1;
}
}
if (storedStrings == this.arraySize){
String[] newArray = new String[this.arraySize+10];
for (int i = 0; i < this.strings.length; i++){
strings[i] = newArray[i];
}
this.strings = newArray;
newArray[storedStrings] = string;
this.arraySize = this.arraySize +10;
}
else{
strings[storedStrings] = string;
}
for(int i = 0; i < strings.length; i++)
{
//System.out.println(strings[i]);
}
}
}
The code is being run in the test class where the error is being generated on line 10 of test class and line 47 of MyArrayList class.
This is the test code
public class TestArrayList{
public static void main(String[] args)
{
MyArrayList a = new MyArrayList(10);
for (int i = 0; i <50; i++){
a.addString("Test" + i);
}
for (int i = 0; i<50;i++){
System.out.println(a.getString(i*5));
}
}
}
you can do it like this:
public void addString(String string){
if (storedStrings == this.arraySize){
this.arraySize += 10;
String[] newArray = new String[this.arraySize];
for (int i = 0; i < this.storedStrings; i++){
newArray[i] = strings[i];
}
this.strings = newArray;
}
if (strings[storedStrings] == null){
strings[storedStrings++] = string;
}
// remove this loop it will show repeating values otherwise
for(int i = 0; i < storedStrings; i++)
{
System.out.println(strings[i]);
}
}
edit: as you are new to java always think about how can you do more with less code, how to avoid repetition of code, how to merge things that do common task. That will help you write better code
edit2 : the problem is with this loop
for (int i = 0; i<50;i++){
System.out.println(a.getString(i*5));
}
if you have 50 elements in array the getString method on (eg) i = 25 will be 25*5 = 125 which is not the index in the array that's why you are getting ArrayIndexOutOfBound Exception.
you can add
public int size(){
return storedStrings;
}
to check the size of your list which is the maximum item that is inside the list
First with your code there is a mistake in this line
strings[i] = newArray[i];
because you aren´t copying the old data to new array but cleaning the strings array, I suppose that you wish do the contrary action.
In other hand you have extra code that you could improve.
public class MyArrayList{
private String[] strings;
private int arraySize;
public MyArrayList(int arraySize){
this.arraySize = arraySize;
this.strings = new String[arraySize];
}
public void addString(String string){
// Since you always do this
// it's better to use a local variale
int storedStrings = 0;
// Use the foreach syntax
// it's less prone to errors
// and easier to read
for (String s : this.strings){
if (s != null){
storedStrings++;
}else{
// since you want to count the strings in your array
// and you put them in this array
// one after the other
// no need to check the whole array
// when you find null you can exit the loop
break;
}
}
if (storedStrings == this.arraySize){
String[] newArray = new String[this.arraySize+10];
for (int i = 0; i < this.strings.length; i++){
// here we need to copy the content of strings in newArray
// NOT the other way
newArray[i] = this.strings[i];
}
this.strings = newArray;
newArray[storedStrings] = string;
this.arraySize += 10;
}else{
this.strings[storedStrings] = string;
}
}
public String[] getStrings(){
return this.strings;
}
}
As for the test class
public static void main(String[] args){
MyArrayList a = new MyArrayList(10);
for (int i = 0; i <50; i++){
a.addString("Test" + i);
}
for (String s : a.getStrings()){
System.out.println(a);
}
}
I'm creating a very simple encoder that will shuffle the characters in a string. I've written it to split this string in half, forming two new variables. The user chooses the number of shuffles they want and that is passed as a parameter in the new class constructor -- which should then use that shuffle value throughout the class. Mine is not. The shuffleEncryption method is using the class variable, 0, instead. I know this must be something very obvious, but I am not catching it. :/
//From Main Class
System.out.println("Enter message to encrypt: ");
String message = input.next();
System.out.print("Number of shuffles: " );
int numShuffles = input.nextInt();
ShuffleCipher shuffle = new ShuffleCipher(numShuffles);
System.out.println(shuffle.encode(message));
//The shuffle class
public class ShuffleCipher implements MessageEncoder {
int shuffle;
public ShuffleCipher(int shuffle) {
shuffle = this.shuffle;
}
private String shuffleEncryption(String str) {
int middle = str.length()/2;
int loop = 1;
System.out.println("shift" + shuffle);
StringBuilder sb = new StringBuilder();
do {
String firstHalf = str.substring(0, middle);
System.out.println("first:" + firstHalf);
String secondHalf = str.substring(middle);
System.out.println("second:" + secondHalf);
for(int i = 0, j = 0; i < firstHalf.length(); i++, j++) {
sb = sb.append(secondHalf.charAt(i));
if(j < secondHalf.length()) {
sb = sb.append(firstHalf.charAt(i));
}
str = sb.toString();
}
loop++;
} while (loop <= shuffle);
return str;
}
#Override
public String encode(String plainText) {
String shuffled;
shuffled = shuffleEncryption(plainText);
return shuffled;
}
}
You are not setting the shuffle member variable in the constructor.
Change this:-
public ShuffleCipher(int shuffle) {
shuffle = this.shuffle;
}
to this:-
public ShuffleCipher(int shuffle) {
this.shuffle = shuffle;
}
I created a class for a bingo game. I get an error saying "'class' expected". How could I return the values in the array to the main starter?
Any other comments would also be helpful.
Thank you.
import java.util.Random;
public class Card
{
Random generator = new Random();
private final int BOARDMAX = 4;
private final int NUMMAX = 59;
int i, j, m, n;
private int [][] ArrayBoard = new int[BOARDMAX][BOARDMAX];
String [][] StrArrayBoard = new String [BOARDMAX][BOARDMAX];
public void RandomNumGenerator()
{
for (i = 0; i<BOARDMAX; i++)
{
for (j = 0; j<BOARDMAX; j++)
{
ArrayBoard[i][j] = generator.nextInt (NUMMAX+1);
}
}
}
public String ShowBoard()
{
for (i = 0; i<BOARDMAX; i++)
{
for (j = 0; j<BOARDMAX; j++)
{
m=i;
n=j;
if (j != BOARDMAX)
StrArrayBoard[m][n] = ArrayBoard[m][n] + " ";
else
StrArrayBoard[m][n] = ArrayBoard[m][n] + " \n";
}
}
return StrArrayBoard[i][j];
}
public void ShowMark()
{
for (i = 0; i<BOARDMAX; i++)
{
for (j = 0; j<BOARDMAX; j++)
{
if (CardCheck [i][j] == 1)
StrArrayBoard[i][j] = ArrayBoard[i][j] + "* ";
else
StrArrayBoard[i][j] = ArrayBoard[i][j] + " ";
if (j == BOARDMAX)
ArrayBoard[i][j] = ArrayBoard[i][j] + "\n";
}
}
}
public String toString()
{
return ArrayBoard[][];
}
}
With toString() you need to return a String object but actually you try to return an int[][]. The same is true for ShowBoard, you try to return an array of Stringarrays which is not a compatible type.
Here's the fix:
public String ShowBoard() {
// your code to populate StrArrayBoard
StringBuilder boardBuilder = new StringBuilder();
for (String[] row:StrArrayBoard)
for (String cell:row)
sb.append(cell);
return boardBuilder.toString();
}
public String toString() {
return ShowBoard();
}
I suggest to refactor the code and rename methods and fields:
ShowBoard() --> getBoardAsString()
ArrayBoard --> arrayBoard
StrArrayBoard --> strArrayBoard
And there's no need to declare StrArrayBoard as a field (class member) just because you only need it inside the ShowBoard method. Declare it there as a local variable.
Adding to the bugs others have pointed:
You have if (CardCheck [i][j] == 1), but the array CardCheck is not declared anywhere.
You have ArrayBoard[i][j] = ArrayBoard[i][j] + "\n"; but ArrayBoard is an int array, you cannot add a string "\n" to it's member.
The compiler will complain because of the error on your code:
public String toString()
{
return ArrayBoard[][];
}
It can't convert int[][] (which is your ArrayBoard) to String. My suggestion is that you populate all values stored in StrArrayBoard in a StringBuffer and return the StringBuffer.toString() in the toString() method.
The toString() method requires a String.
Hope this helps.
public String toString()
{
return ArrayBoard[][];
}
This method expects to return a String but you are returning a 2D Integer array, what you need is a String. the toString() method returns a string representation of the object, so in this case, what you can do is to use a StringBuilder to build the string representation of the array and then, use the .toString() of the StringBuilder to return the string representing the 2D Array.
Also, as noted by Alois Cochard, you variable naming does not follow convention. Variable names in Java use a camel case notation.
I for one don't really understand your question but I've got a couple of comments.
The class variables i and j should be local variables in each method.
Your naming convention is nonstandard, seems like a more C# convention. Start variable and method names with a lower case.
CardCheck isn't defined anywhere. I presume it is meant to indicate if a number on a square has been checked, in which case it should be a boolean and not an int.
toString doesnt return a string. You can use Arrays.toString to help you.
Similarily, ShowBoard just returns one element of an array, you probably wanted to show the entire board there.
For your toString and ShowBoard methods you probably want to use a StringBuilder to build up the string representation.
StringBuilder builder = new StringBuilder();
for (int i=0; i<BOARDMAX; i++) {
for (int j=0; j<BOARDMAX; j++) {
builder.append(StrArrayBoard[i][j]);
}
builder.append('\n');
}
return builder.toString();
Here's a version of your class that compiles (and I changed some field names and modifiers to adhere to standard conventions). Try this:
public class Card{
private final Random generator = new Random();
private static final int BOARDMAX = 4;
private static final int NUMMAX = 59;
int i, j, m, n;
private final int[][] arrayBoard = new int[BOARDMAX][BOARDMAX];
private final String[][] strArrayBoard = new String[BOARDMAX][BOARDMAX];
// do something here please
private int[][] CardCheck;
public void RandomNumGenerator(){
for(i = 0; i < BOARDMAX; i++){
for(j = 0; j < BOARDMAX; j++){
arrayBoard[i][j] = generator.nextInt(NUMMAX + 1);
}
}
}
public String ShowBoard(){
for(i = 0; i < BOARDMAX; i++){
for(j = 0; j < BOARDMAX; j++){
m = i;
n = j;
if(j != BOARDMAX){
strArrayBoard[m][n] = arrayBoard[m][n] + " ";
} else{
strArrayBoard[m][n] = arrayBoard[m][n] + " \n";
}
}
}
return strArrayBoard[i][j];
}
public void ShowMark(){
for(i = 0; i < BOARDMAX; i++){
for(j = 0; j < BOARDMAX; j++){
if(CardCheck[i][j] == 1){
strArrayBoard[i][j] = arrayBoard[i][j] + "* ";
} else{
strArrayBoard[i][j] = arrayBoard[i][j] + " ";
}
if(j == BOARDMAX){
// this is probably what you mean:
strArrayBoard[i][j] = arrayBoard[i][j] + "\n";
}
}
}
}
#Override
public String toString(){
// this is probably what you mean:
return Arrays.deepToString(strArrayBoard);
}
}