How to replace elements in a 2D array in Java? Okay so for my program, I am tryi
ID: 3884049 • Letter: H
Question
How to replace elements in a 2D array in Java? Okay so for my program, I am trying to create a fish tank. My program is to generate 4 different FISH: ><))'> in a tank of tilde (~) characters. The tank is a 2D array of 8 rows and 32 columns so it would look like ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ for one of the eight rows (before I generate the random positions of the fish in the rank). Then one row could look like ~~~~~~~~~~><))'>~~~~~~~~~~~~~~~~ after I generate random positions for my fish. It should also hide characters of the fishes body if it is more to the left like such )'>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ where there is only three parts of the fish, 2 body characters and the head character.The random position coordinate I have generated for each of the four fishes starts on the head of the fish (>) which means I have been able to successfully generate four > in the tank, which looks like ~~~~~~~~~~~~~~~~>~~~~~~~~~~~~~~~ when ran. But my problem is how I can get the rest of the fishes body after the head. I know I am going to be working backwards from the > character and replace the tilde characters with characters from the fishes body. Some steps that would explain it and some suggestions would be nice. I am just getting back into basic coding so a good explanation would be VERY HELPFUL since some "experts" on Chegg don't always see through the student's eyes. Here is some of the code below.
import java.util.Random;
public class Main {
public static void main(String[] args) {
char [][] tilde = new char [8][32];
fillTank(tilde, '~');
int fish [][] = generateRandomPositions(4, 8, 32);
for (int i = 0; i < fish.length; ++i) {
placeFishInTank(tilde, fish[i][0], fish[i][1]);
}
renderTank(tilde);
}
/**
* Copies the water character into every position in the tank array. The two-dimensional tank
* array can have dimensions of any size(s).
*
* @param tank will contain all water characters after this method is called.
* @param water is the character copied into the tank.
*/
public static void fillTank(char[][] tank, char water)
{
for (int row = 0; row < tank.length; ++row) {
for (int column = 0; column < tank[row].length; ++column) {
tank [row][column] = '~';
}
System.out.println();
}
}
public static void placeFishInTank(char [][] positionInTank, int x, int y) { //HERE IS WHERE I AM GETTING MESSED UP
positionInTank[x][y] = '>';
String fishBody = "><))'";
char[] fishBodyArray = fishBody.toCharArray();
int j = 4;
for (int i = y - 1; i >= 0; i--) {
positionInTank[x][i] = fishBodyArray[j];
j--;
}
}
// for (int i = 0; i < positionInTank.length - 1; i++) {
// positionInTank[i] = positionInTank[i - 1];
// positionInTank[i] = '(';
// for (int j = 0; i < positionInTank[x].length-1; j++)
// if (positionInTank[][] >= 0) {
// String.charAt(i, j);
// }
// }
//if (positionInTank[row].length - 1 != 0) {
//add on next character '''
// }
//if (!positionInTank[row] - 2 != 0) {
//add on next character ')'
// }
//if (!positionInTank[row] - 3 != 0) {
//add on next character ')'
// }
//if (!positionInTank[row] - 4 != 0) {
//add on next character '<'
// }
//if (!positionInTank[row] - 5 != 0) {
//add on next character '>'
// }
/**
* Prints the contents of the tank into the console in row major order, so that the
* smallest row indexes are on top and the smallest column indexes are on the left. For
* example:
* tank[0][0] tank[0][1] tank[0][2] ...
* tank[1][0] tank[1][1] tank[1][2] ...
* ...
* Each row is on its own line, and this method should work for two-dimensional tanks with
* dimensions of any size.
*
* @param tank contains the characters that will be printed to the console.
*/
public static void renderTank(char[][] tank)
{
for (int row = 0; row < tank.length; ++row) {
for (int column = 0; column < tank[row].length; ++column) {
System.out.print(tank[row][column]);
}
System.out.println();
}
}
public static int[][] generateRandomPositions(int number, int width, int height) //width and height different
{
int [][] fish = new int [number][2];
for (int i = 0; i < number; ++i) {
fish [i][0] = Utility.randomInt(width);
fish [i][1] = Utility.randomInt(height);
}
return fish;
}
}
I keep getting back
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
at Main.placeFishInTank(Main.java:41)
at Main.main(Main.java:10)
Explanation / Answer
String fishBody = "><))'"; you don't need to escape ' char. Though it should not have any effect.
Second issue in your code is in for loop for putting fish body in tank
for (int i = y - 1; i >= 0 && j >= 0; i--) {
positionInTank[x][i] = fishBodyArray[j];
j--;
}
Here you need to make sure that j is also greater than 0 because y can be very far
say y = 31, now figh will be rendered from 26-31 but with the loop you have you will keep on going beyond hat until i is not -1 but there is no char in figh to access for i = 25 as fish[-1] do not exist.
Hope it helped.
Here is full code (Please note you haven't shared Utility class which you are using for getting random int and I hope that class is returning you values which are making sure fish are not overlapping each other)
import java.util.Random;
public class Main {
public static void main(String[] args) {
char [][] tilde = new char [8][32];
fillTank(tilde, '~');
int fish [][] = generateRandomPositions(4, 8, 32);
for (int i = 0; i < fish.length; ++i) {
placeFishInTank(tilde, fish[i][0], fish[i][1]);
}
renderTank(tilde);
}
/**
* Copies the water character into every position in the tank array. The two-dimensional tank
* array can have dimensions of any size(s).
*
* @param tank will contain all water characters after this method is called.
* @param water is the character copied into the tank.
*/
public static void fillTank(char[][] tank, char water)
{
for (int row = 0; row < tank.length; ++row) {
for (int column = 0; column < tank[row].length; ++column) {
tank [row][column] = '~';
}
}
}
public static void placeFishInTank(char [][] positionInTank, int x, int y) { //HERE IS WHERE I AM GETTING MESSED UP
positionInTank[x][y] = '>';
String fishBody = "><))'";
char[] fishBodyArray = fishBody.toCharArray();
int j = 4;
for (int i = y - 1; i >= 0 && j >= 0; i--) {
positionInTank[x][i] = fishBodyArray[j];
j--;
}
}
// for (int i = 0; i < positionInTank.length - 1; i++) {
// positionInTank[i] = positionInTank[i - 1];
// positionInTank[i] = '(';
// for (int j = 0; i < positionInTank[x].length-1; j++)
// if (positionInTank[][] >= 0) {
// String.charAt(i, j);
// }
// }
//if (positionInTank[row].length - 1 != 0) {
//add on next character '''
// }
//if (!positionInTank[row] - 2 != 0) {
//add on next character ')'
// }
//if (!positionInTank[row] - 3 != 0) {
//add on next character ')'
// }
//if (!positionInTank[row] - 4 != 0) {
//add on next character '<'
// }
//if (!positionInTank[row] - 5 != 0) {
//add on next character '>'
// }
/**
* Prints the contents of the tank into the console in row major order, so that the
* smallest row indexes are on top and the smallest column indexes are on the left. For
* example:
* tank[0][0] tank[0][1] tank[0][2] ...
* tank[1][0] tank[1][1] tank[1][2] ...
* ...
* Each row is on its own line, and this method should work for two-dimensional tanks with
* dimensions of any size.
*
* @param tank contains the characters that will be printed to the console.
*/
public static void renderTank(char[][] tank)
{
for (int row = 0; row < tank.length; ++row) {
for (int column = 0; column < tank[row].length; ++column) {
System.out.print(tank[row][column]);
}
System.out.println();
}
}
public static int[][] generateRandomPositions(int number, int width, int height) //width and height different
{
int [][] fish = new int [number][2];
for (int i = 0; i < number; ++i) {
fish [i][0] = Utility.randomInt(width);
fish [i][1] = Utility.randomInt(height);
}
return fish;
}
}
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