Empty an array in Java / processing

Question

除了遍历数组中的每个元素并将每个元素设置为null之外，Java /处理中是否有一个本机函数来简单地清空一个数组（或者将其销毁，以便能够将其重新声明为一个新数组）？

Answer 1

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.

Answer 2

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.

Answer 3

array = new String[array.length];

Answer 4

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);
}

Answer 5

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

ie

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];

Answer 6

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);
  }
}

Answer 7

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.

Answer 8

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 = [];