Problems with arrays & for loops

[Karl Davies]

Hello! I'm incredibly new to Java and programming. The problem I'm having with this piece of code is the marked for loop (or at least I think it is), I want it to take all all elements below 10 and copy them into array10 but it just isn't doing that and I'm not sure where I've gone wrong. Help would be brilliant Thanks.

 import java.util.*;
public class Exercise1
{
	public static void main(String args[])
	
	{
		System.out.print("Histogram Display\n*****************\n");
		int NULL = -1;
		int y;
		int [] randArray = new int [80];
		int [] array10 = new int [80];
		java.util.Arrays.fill(array10, NULL);
		int [] array20 = new int [80];
		int [] array30 = new int [80];
		int [] array40 = new int [80];
		int [] array50 = new int [80];
		int [] array60 = new int [80];
		int [] array70 = new int [80];
		int [] array80 = new int [80];
		int [] array90 = new int [80];
		int [] array100 = new int [80];
		Random RandGen = new Random();
		
		for (int x = 0; x < randArray.length; x++) {
			randArray[x] = RandGen.nextInt(100);
		}
		Arrays.sort(randArray);
		for(int x = 0; x < randArray.length; x++) {       //MARKED
			if (x < 10) {
				System.arraycopy(randArray, x, array10, x, x);
			}
		}		

		for (int x = 0; x < array10.length; x++) {
			if (array10[x] == NULL) {
				System.out.println("null");
			} else {
				System.out.println("not null");
			}
		}
		System.out.print("\t");
		for (int x = 0; x < array10.length; x++) {
			if (x != -1) {
				System.out.print(array10[x] + "\t");
				System.out.print(randArray[x] + "\n\t");
			}
		}	
	}
}   

[Joanne Neal]

In your MARKED for loop, x is not the value of an array element - it's the index of an array element. The value is represented by randArray[x].

Also, you don't need to use system.arraycopy to copy a single array element. Just use

array10[x] = randArray[x];

And just for the record, your parameters to System.arraycopy are wrong. The last parameter is the number of values to copy, so the first time round the loop you copied none, the second time one, the third time two, etc

[Karl Davies]

Brilliant! It's in working order now, thank you Joanne!

[Wouter Oet]

Why not create a 2D array?

int[][] arrays = new int[10][];
for(int i=0; i<arrays.length; i++)
   arrays[i] = new int[10];    

[Campbell Ritchie]

And welcome to the Ranch