Let's that I have a number N. N will be the size of the array.
int numArray [] = new numArray[N];
However, the contents of the array will hold every other number from 1 to positive N. This means that the entire size N array will not be full after that for loop. So after the for loop, I want to trim (or resize) the array so that there will no longer be any empty slots in the array.
Example :
Let's say N = 5; That means, after the for loop, every other number from 1 to 5 will be in the array like so:
int arr[] = new int[N];
int arr[0]=1;
int arr[1]=3;
int arr[2]= null;
int arr[3]= null;
int arr[4]= null;
Now, I want to trim (or resize) after the for loop so that the indexes that hold null will be gone and then the array should be:
int arr[0]=1;
int arr[1]=3;
The size of the array is now 2.
You can't trim an array. The fastest approach is just to copy it into a smaller one, using System.arraycopy, which is almost always much faster than a for loop :
int somesize = 5;
int[] numArray = new int[somesize];
//code to populate every other int into the array.
int[] smallerArray = new int[somesize/2];
//copy array into smaller version
System.arraycopy(numArray, 0, smallerArray, 0, somesize / 2);
You can't change the size of an array in Java after it has been created. What you can do however, is to create a new array of the size that you need.
Another important point is that you are creating an array of a primitive : int
. Primitives are not objects and you cannot assign the value null
to a primitive. You need to create an array of java.lang.Integer
if you want to be able to set entries in it to null
.
Integer[] numArray = new Integer[N];
Thanks to a Java feature called auto-boxing , almost all code that works with primitive int
values, also works with Integer
values.
Steps:
Integer[]
instead of int[]
null
entries in original array)null
value from it to the new array.Code:
Integer[] oldArray = ...;
// Step 2
int count = 0;
for (Integer i : oldArray) {
if (i != null) {
count++;
}
}
// Step 3
Integer[] newArray = new Integer[count];
// Step 4
int index = 0;
for (Integer i : oldArray) {
if (i != null) {
newArray[index++] = i;
}
}
I think there is a bit shorter way to do the trimming itself. Whats left is to find the proper index.
You can do:
int someIndex = Arrays.asList(arr).indexOf(null);
arr = Arrays.copyOfRange(arr,0,someIndex);
You surely better of with some more appropriate data structure, for example a list or a set depending on what's your intention with it later. That way you don't even need to create an N sized structure just so you'd have to reduce it anyway. Rather you create an empty list and add the elements that you actually need
import java.util.Arrays;
public static void main( String[] args )
{
int[] nums2 = {9,4,1,8,4};
nums2 =Arrays.copyOf(nums2,3);
for (int i : nums2) {
System.out.print(i+" ");
}
}
//Output
9 4 1
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