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How to draw a triangle in a 2D array (Java)

For a class project we need to be able to draw a triangle in a 2D array of chars. Algorithmically I can't work out how to do it.
My current code is this (but it does not work):
public void fill() {
for (int i = 0; i < h; i++) {
double x=h;
while(x<=0){
drawing.setPoint(i, x, myChar);
x=Math.ceil(x/2);
}
}
}
I want the output to look something like this:
....*....
...***...
..*****..
.*******.
*********
We can't use any pre-existing methods or classes that relate to drawing.
Thanks for your help

Based on your drawing, you need 9 columns for 5 rows. So,
int height = 5;
int width = 2*height - 1;
Even though I'm not sure what drawing.setPoint(i, x, myChar); does, I think this example will get you going. I will build a String based on chars.
char fill = '*';
char blank = '.';
I'll start the rows at 0 but the columns at 1 to make the math a little clearer.
For row = 0, ....*.... you need one star in column = 5.
For row = 1, ...***... you need three stars in column = 4,5,6.
For row = 3, .*******. you need seven stars in column = 2,3,4,5,6,7,8.
Notice that for row i you need a star in column j if the distance between the height = 5 and the column j is less than or equal to i. That is, when | height - column | <= row
for (int row = 0; row < height; row ++) {
StringBuilder line = new StringBuilder(width);
for (int column = 1; column <= width; column ++) {
char out = Math.abs(column - height) <= row ? fill : blank;
line.append(out);
}
System.out.println(line);
}
This yields
....*....
...***...
..*****..
.*******.
*********
I assume you can use Math.abs since your example has Math.ceil. If not, you can convert Math.abs to an if statement.

There are lots of ways to tackle this, and you've already seen one answer which draws the picture row-by-row.
I'm going to assume that you've already got routines to create char[][] and to print the characters in that array of arrays to the screen. It looks as if you already have a setPoint() method too, to poke a point into the structure.
As a beginner, I don't think it helps you to be given a solution. You need to be pointed in the right direction to solve it yourself.
Lots of experienced coders now use Test Driven Design, and you could learn from this: start with a simple case, create a test for that, make that test pass, repeat with more tests until there are no more tests to write.
Eventually you should learn a test framework like jUnit, but for now you can "test" by just running your program. So the first test is, does it work for height == 1?
You can pass this test (for now that means, run the program and see that the output looks right) with:
public void drawTriangle(int height) {
drawing.setPoint(0,5,'*')
}
Job done.
Now to make it work for height==2:
public void drawTriangle(int height) {
drawing.setPoint(0,5,'*');
if(height == 2) {
drawing.setPoint(1,4,'*');
drawing.setPoint(1,5,'*');
drawing.setPoint(1,6,'*');
}
}
This still works for height == 1, but also works for height == 2.
But you can immediately see an opportunity for a loop to replace those three commands for the second row. So:
public void drawTriangle(int height) {
drawing.setPoint(0,5,'*');
if(height == 2) {
for(int 4; i<7; i++) {
drawing.setPoint(1,i,'*');
}
}
}
... and you can pull that out into a method:
public void drawTriangle(int height) {
drawing.setPoint(0,5,'*');
if(height == 2) {
drawRow2();
}
}
private void drawRow2() {
for(int 4; i<7; i++) {
drawing.setPoint(1,i,'*');
}
}
This is called refactoring -- writing something that works, but isn't written the best way, testing it to ensure it works, then changing the way it's written one step at a time, so it still works, but in a tidier way.
Hopefully you can see where this is going. You can modify drawRow2() to be more general -- drawRow(int rowNumber), and gradually replace the literal numbers in there with variables derived from rowNumber. Then you can use drawRow(0) to draw the first row, and drawRow(1) to draw the second. Then you can draw a three row triangle by adding drawRow(2), and then you can improve that by using a loop instead.

Java Android trying to place a 10*10 grid over a bitmap to see how much of a colour is in each grid section

to describe my issue I must first discuss what I am trying to do, http://i.imgur.com/rcHwze5.png here is an image of a letter with a 10*10 grid over it. For every box in the grid if 1/3 of the pixels are colored a 1 is added to the ArrayList, otherwise a 0 is added. Here is my 3 methods that I have created to do this: https://gist.github.com/VincentMc/7ddf3c282e80bbff7835 BoundBM is a bitmap object with the letter drawn onto it.
Here is an image of my desired output http://i.imgur.com/B0QnUW8.png
Here is an image of my actual output http://i.imgur.com/WgRVXLv.png
It seems once a 1 is added on a row it is constantly added until it reaches the next row, but I can't seem to see why??
Any help would be greatly appreciated I have been at this quite a while, Thanks!

do it in two step:
1: sort each string:
public String sortString(String s1){
char[] chars = s1.toCharArray();
Arrays.sort(chars);
String sorted = new String(chars);
return sorted;
}
2: put each of your string in an array and use:
Arrays.sort(stringArray);

Out of the Code-Segmet you offered, i cant see an obvious mistake. But your design is inviting mistakes. To avoid these you may try:
Don't use count as a classwide variable, thou its not relevant for the hole class but only for the method. So make it an return statement, that you dont loose control over it, that it may be set anywhere or is only changed locally in a method.
totalp should not be calculated in every countPixel() method call, because it is a fixed value for your BoundBM. Initialize it in your constructor maybe, or with loading the bitmap.
At last, you know how large your output array is supposed to be, it doesnt make much sense for me, to keep it a list and to add it. Create an 2D array, and write it directly.
Hope it will help
reineke
EDIT: found the mistake!
in code line 27 you set x to 0 and not to the initial value of the input x, so you continue at the wrong position!!
Here is what i would do:
final int GRID=10;
totalp = boundBM.getWidth()/GRID * boundBM.getHeight()/GRID;
//this method now does not need to read boundBM, so it is more opject-oriented
public int countPixels(int x, int y, int h, int w){
count = 0;
for (i=x; i<x+w; i++){
for(k =y; k<y+h; k++){
if(c != boundBM.getPixel(i, k)) count++;
}
}
//funny thing
return (count>totalp/3) ? 1 : 0;
}
public void createNeuralInput(){
int h = boundBM.getHeight()/GRID;
int w = boundBM.getWidth()/GRID;
int[][] array= new int[GRID][GRID];
for(int i = 0; i < GRID; i++) {
for(int j = 0; j < GRID ; j++) {
n1.add(countPixels(i*h, j*w, h, w));
//i would prefer:
//array[i][j]=countPixels(i*h, j*w);
}
}
}

How to draw a simple graph?

So here's the thing, I'm supposed to read a document and import some data.
A line in the document looks like this "A 0 2 5 20 23 25." (.txt).
I can write a method that finds this line and the values but my problem is to draw the actual graph whith the values. X of the graph will be fixed for 10 between each value and the values in the file corresponds to Y. I want to come up with a method that takes the first Y(0), and Draws a straight line to the next Y(2) and from 2-5 etc.
I fail to do this, my method only Draws a line from 0-2 and 5-20 and 23-25.
Book hasn't talked about array's yet so I should do this without arrays, I try to do it as I read the file but..
Here is a bit of my code anyway, any tips?? Much appreciated
public static void drawGraph(String letter, Scanner input, Graphics g){
while (input.hasNextLine()){
int x = 1;
String text = input.nextLine();
Scanner data = new Scanner(text);
String foundLetter = data.next();
if(foundLetter.equalsIgnoreCase(letter)){
while(data.hasNextInt()){
int count = data.nextInt();
//This is where I get Stuck
g.drawLine((x-1)*10, y1, 10*x);
x++;
}
}
}
}
I have made an template drawingpanel for the plot divided into sections of 10's
Thanks,

You have to memorize the last y value, then draw a line from (x-1, last y) to (x, y).
int lastY = data.nextInt();
while (data.hasNextInt()) {
int nextY = data.nextInt();
g.drawLine((x-1)*10, lastY, 10*x, nextY);
x++;
lastY = nextY;
}

Mapping unique points to unique integer index

I am not familiar with coordinate systems or much of the math dealing with these things at all. What I am trying to do is take a Point (x,y), and find its position in a 1 dimensional array such that it follows this:
(0,2)->0 (1,2)->1 (2,2)->2
(0,1)->4 (1,1)->5 (2,1)->6
(0,0)->8 (1,0)->9 (2,0)->10
where the arrows are showing what value the coordinates should map to. Notice that an index is skipped after each row. I'm think it'll end up being a fairly trivial solution, but I can't find any questions similar to this and I haven't had any luck coming up with ideas myself. I do know the width and height of the 2 dimensional array. Thank you for any help!
My question is perhaps ambiguous or using the wrong terminology, my apologies.
I know that the coordinate (0,0) will be the bottom left position. I also know that the top left coordinate should be placed at index 0. Each new row skips an index by 1. The size of the coordinate system varies, but I know the number of rows and number of columns.

First step, flip the values upside down, keep points in tact:
(0,2)->8 (1,2)->9 (2,2)->10
(0,1)->4 (1,1)->5 (2,1)->6
(0,0)->0 (1,0)->1 (2,0)->2
You'll notice that y affects the output by a factor of 4 and x by a factor of 1.
Thus we get a very simple 4y + x.
Now to get back to the original, you'll notice the transformation is (x,y) <- (x,2-y) (that is, if we transform each point above with this transformation, we get the original required mapping).
So, substituting it into the equation, we get (2-y)*4 + x.
Now this is specific to 3x3, but I'm sure you'll be able to generalize it by replacing 2 and 4 by variables.

If you want to reduce the dimension and avoid overlapping you need a space-filling-curve, for example a morton curve. Your example looks like a peano curve because it's a 3x3 matrix. These curves is difficult to calculate but have some nice things. But if you just look for self-avoiding curves you can create your own? Read here: http://www.fractalcurves.com/Root4Square.html.

I was beaten to the formula, here is the bruteforce using a Map.
public class MapPointToIndex {
private Map<Point, Integer> map;
private int index, rowcount;
public MapPointToIndex(int rows, int columns) {
map = new HashMap<Point, Integer>();
for (int i = rows - 1; i >= 0; i--) {
index += rowcount;
for (int j = 0; j < columns; j++) {
Point p = new Point(j, i);
map.put(p, index);
index++;
}
rowcount = 1;
}
}
public int getIndex(Point point){
return map.get(point);
}
public static void main(String[] args) {
MapPointToIndex one = new MapPointToIndex(3, 3);
System.out.println(one.map);
}
}
Out:
{java.awt.Point[x=0,y=0]=8, java.awt.Point[x=2,y=2]=2, java.awt.Point[x=1,y=2]=1, java.awt.Point[x=2,y=1]=6, java.awt.Point[x=1,y=1]=5, java.awt.Point[x=2,y=0]=10, java.awt.Point[x=0,y=2]=0, java.awt.Point[x=1,y=0]=9, java.awt.Point[x=0,y=1]=4}

Printing a square of stars in Java

Hi I have been given a task for my course and it is to create an algorithm to make a 5 by 5 square like below:
*****
*****
*****
*****
*****
I've spent hours attempting to do it and read tutorials and books. It's so frustrating as I know it must be so easy if you know what you are doing. Can anyone give me any guidance as to where to start?

You probably know and understand how to create a "Hello World" style program in Java.
Now think - how would you go about having that same program print 5 times "Hello World"?
After that, think about how you would make it write N times "Hello World".
After that, think about how you would output a series of N stars.
Good luck!

Seems like you should have a variable x equal to the dimension (5). A for loop i that loops from 1-x. In it a for loop j that loops from 1-x. The j loops outputs *, or appends * to a string. After the j loop, the i loop does a new line.
This solution will allow for a square grid of any size.
int size = input;
for (i=0; i<size; i++){
for (j=0; j<size; j++){
// output a single "*" here
}
// output a new line here
}

If I got you right, then it's about a NxN square with a given N. Your question is just about N := 5, but your comments let me assume that you've to program a more general solution.
Split the work that have to be done into more basic and smaller problems:
create a String that contains * N times.
call System.out.println() with the generated String N times

This will work for you as well, but the professor will frown that you found the answer online and did not think of it yourself.
System.out.println("*****\n*****\n*****\n*****\n*****");

Here's how I did it:
class Main {
public static void main(String[] args) {
int size = 25;
int pos = 0;
for(int i = 0; i<size; i++){
if(pos % 5 == 0){
System.out.println();
}
System.out.print("*");
pos++;
}
}
}

If I understood correctly, what you need is a console output with 5 lines of stars.
You can outpt text to console with System.out.print() or System.out.println() with the second option making a line break.
As you have to repeat the output, it is advisable to do enclose the output statement in a loop. Better in a nested loop to separate the x and the y axis.
In order to make the output modifiable - for the case you will need to output a 6x6 or 12x15 square tomorrow without any code modification, I would make the limits of the loop parametrized.
All in all, something like this :
public void printStartSquare(int width, int height){
for(int i = 0; i < height;i++){
for(int j = 0; j < width;j++){
System.out.print("*");
}
System.out.println("");
}
}