Arrays.fill

Learn to fill arrays with Arrays.fill.

Filling arrays: Arrays.fill

To fill every slot of an array with the same value you use Arrays.fill. This is very practical for setting initial values.

int[] board = new int[5];
Arrays.fill(board, 0);
// board: {0, 0, 0, 0, 0}

The first parameter is the array, the second is the value. The method changes the array in place; it does not return a new array. It is ideal for resetting game boards, counters or flag arrays.

Filling a portion of the array

Arrays.fill is overloaded: you can pass start and end indices to fill only part of the array. The end index is exclusive.

int[] row = new int[5];
Arrays.fill(row, 1, 4, 9);
// row: {0, 9, 9, 9, 0}

Indices 1, 2, 3 become 9; indices 0 and 4 stay untouched. This is handy for tasks like marking the middle of a row.

Exercise Reset the score board

Create an int[] array of 5 elements, set every slot to -1 with Arrays.fill, then print the array using Arrays.toString.

Show example solution

int[] board = new int[5];
Arrays.fill(board, -1);
System.out.println(Arrays.toString(board));

Test yourself

Match scenario to method

Sort the array

Arrays.sort
Convert the array to text

Arrays.toString
Same value to all slots

Arrays.fill
Take a new copy

Arrays.copyOf
What does Arrays.fill return?
- It returns the first element
- It returns a new filled array
- It returns the number of filled slots
- void; it modifies the array in place
Show answer

void; it modifies the array in place — fill is a void method; it fills the array in place.

Fill in the blank: set all slots to 1

int[] flags = new int[4];
Arrays.____(flags, 1);

Show answer

int[] flags = new int[4];
Arrays.fill(flags, 1);

Next lesson: Summary - Array methods

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