CODEWITHSUNDEEP
javaarraysprocessing
ina
ina

Reputation: 19534

Empty an array in Java / processing

Other than looping through each element in an array and setting each one to null, is there a native function in Java / processing to simply empty an array (or destroy it, to be able to redeclare it as a new array)?

Upvotes: 63

Views: 394940

Answers (8)

Cesar Duran
Cesar Duran

Reputation: 377

I was able to do that with the following 2 lines, I had an array called selected_items used to get all selected items on a dataTable 

selected_items = null;
selected_items = [];

Upvotes: -1

Suraj Mahli
Suraj Mahli

Reputation: 39

If Array xco is not final then a simple reassignment would work:

i.e.

xco = new Float[xco .length];

This assumes you need the Array xco to remain the same size. If that's not necessary then create an empty array:

xco= new Float[0];

Upvotes: 4

Shiqing Fan
Shiqing Fan

Reputation: 708

Take double array as an example, if the initial input values array is not empty, the following code snippet is superior to traditional direct for-loop in time complexity:

public static void resetValues(double[] values) {
  int len = values.length;
  if (len > 0) {
    values[0] = 0.0;
  }
  for (int i = 1; i < len; i += i) {
    System.arraycopy(values, 0, values, i, ((len - i) < i) ? (len - i) : i);
  }
}

Upvotes: 5

R.Moeller
R.Moeller

Reputation: 3446

Faster clearing than Arrays.fill is with this (From Fast Serialization Lib). I just use arrayCopy (is native) to clear the array:

static Object[] EmptyObjArray = new Object[10000];

public static void clear(Object[] arr) {
    final int arrlen = arr.length;
    clear(arr, arrlen);
}

public static void clear(Object[] arr, int arrlen) {
    int count = 0;
    final int length = EmptyObjArray.length;
    while( arrlen - count > length) {
        System.arraycopy(EmptyObjArray,0,arr,count, length);
        count += length;
    }
    System.arraycopy(EmptyObjArray,0,arr,count, arrlen -count);
}

Upvotes: 3

AlexR
AlexR

Reputation: 115338

I just want to add something to Mark's comment. If you want to reuse array without additional allocation, just use it again and override existing values with new ones. It will work if you fill the array sequentially. In this case just remember the last initialized element and use array until this index. It is does not matter that there is some garbage in the end of the array.

Upvotes: 2

jjnguy
jjnguy

Reputation: 138884

You can simply assign null to the reference. (This will work for any type of array, not just ints)

int[] arr = new int[]{1, 2, 3, 4};
arr = null;

This will 'clear out' the array. You can also assign a new array to that reference if you like:

int[] arr = new int[]{1, 2, 3, 4};
arr = new int[]{6, 7, 8, 9};

If you are worried about memory leaks, don't be. The garbage collector will clean up any references left by the array.

Another example:

float[] arr = ;// some array that you want to clear
arr = new float[arr.length];

This will create a new float[] initialized to the default value for float.

Upvotes: 43

Mark Peters
Mark Peters

Reputation: 81074

There's

Arrays.fill(myArray, null);

Not that it does anything different than you'd do on your own (it just loops through every element and sets it to null). It's not native in that it's pure Java code that performs this, but it is a library function if maybe that's what you meant.

This of course doesn't allow you to resize the array (to zero), if that's what you meant by "empty". Array sizes are fixed, so if you want the "new" array to have different dimensions you're best to just reassign the reference to a new array as the other answers demonstrate. Better yet, use a List type like an ArrayList which can have variable size.

Upvotes: 87

Adam
Adam

Reputation: 44939

array = new String[array.length];

Upvotes: 8

Related Questions