So I'm trying to get a binary search method working, while displaying an on screen GUI that sorts through the array that is printed in the world;
And getting it to change the background colour of the boxes behind it to show it doing a bubble sort.
Here is the code that deals with the colour changing:
Now this all works up to the point where I want to run my binary search method:
All of this code is within my world class, there is a tiny bit of information in another class "Number" Do you want to see that code also?
So when I right click in the world and call on the binarySearch method, it does nothing and then a terminal window will pop up (well really it's already up) and say:
I'm fairly new to Java and Greenfoot and I was hoping someone might be able to help with this problem and explain what it means.
Thanks
public void printArrayinWorld()
{
for (int count=0; count<array.length; count++) {
int htextoffset = -3;
int vtextoffset = 7;
int width = 40;
int height = 40;
GreenfootImage img = new GreenfootImage(width,height);
img.setColor(new Color(0,0,192,192));
img.fillRect(15,15,width,height);
img.setColor(Color.WHITE);
Font font=new Font("Arial",Font.BOLD,12);
img.setFont(font);
String number = Integer.toString(array[count]); //convert value of the array to a string
img.drawString(number,width/2+htextoffset,height-vtextoffset); //draw an image from the converted string
Actor arrayItem = new Number(count, array[count]);
arrayItem.setImage(img);
addObject(arrayItem,1,count*1+1);
}
}public void bubbleSort()
{
System.out.println("Before sorting, the array is organised as: "+array[0]+", "+ array[1]+", " +array[2]+", " +array[3]+", " +array[4]+", "+array[5]+", "+array[6]+", "+array[7]+", "+array[8]);
System.out.println();
// boolean swapped = true;
// int index = 0;
// int temp = 0;
while (swapped)
{
swapped = false;
index = 0;
Greenfoot.start();
while ( index < array.length - 1)
{
if (array[index] > array[index +1])
{
//Greenfoot.setSpeed(60);
changeNumberBGcolour(index, 153, 255, 0);
changeNumberBGcolour(index + 1, 235, 251, 121);
Greenfoot.delay(30);
temp = array[index + 1];
array[index + 1] = array[index];
array [index] = temp;
swapped = true;
removeArrayfromWorld();
printArrayinWorld();
Greenfoot.delay(30);
}
index = index +1;
}
}
printArray();
System.out.println("After sorting, the array is organised as: "+array[0]+", "+ array[1]+", " +array[2]+", " +array[3]+", " +array[4]+", "+array[5]+", "+array[6]+", "+array[7]+", "+array[8]);
Greenfoot.stop();
}public void changeNumberBGcolour(int index, int r, int g, int b)
{
Number arrayitem = (Number) getNumberFromArray(index);
GreenfootImage img = new GreenfootImage(40,40);
img = arrayitem.getImage();
int htextoffset = 0;
int vtextoffset = 7;
int width = 40;
int height = 40;
img.setColor(new Color(r,g,b));
//img.setColor(new Color(153,255,0));
// 153,255,0 = brightgreen
// 235,251,121 = limegreen
img.fillRect(15,15,width,height);
img.setColor(Color.WHITE);
Font font=new Font("Arial",Font.BOLD,12);
img.setFont(font);
String value = Integer.toString(arrayitem.value); //convert value of the array to a string
img.drawString(value,width/2+htextoffset,height-vtextoffset); //draw an image from the converted string
}public void binarySearch(int item)
{
int low = 0;
int high = array.length;
boolean found = false;
// int middle = 0;
// int value = 0;
// int index = 0;
//Greenfoot.start();
while ( high >= low & found == false)
{
middle = (high - low)/2;
//changeNumberBGcolour(index, 153, 255, 0);
//changeNumberBGcolour(index + 1, 235, 251, 121);
Greenfoot.delay(30);
if ( value < array[middle])
{
high = middle - 1;
//changeNumberBGcolour(index, 153, 255, 0);
}
else if (value == array[middle])
{
found = true;
}
else
{
low = middle + 1;
changeNumberBGcolour(index + 1, 235, 251, 121);
}
if ( found )
{
System.out.println("Found number " +item +" in the array.");
}
else
{
System.out.println("Could not find number " +item+" in the array.");
}
}
//Greenfoot.stop();
}java.lang.NullPointerException at bubble.changeNumberBGcolour(bubble.java:164) at bubble.binarySearch(bubble.java:258)
