VulnTech Handy Tools: The Arrays Class | Learn Java

Printing a whole array

Printing an array directly gives a strange code. Arrays.toString prints it nicely:

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] nums = {5, 2, 9, 1};
        System.out.println(Arrays.toString(nums));
    }
}

Output

[5, 2, 9, 1]

Common Arrays tools

Tool	Does
`Arrays.toString(a)`	turns the array into readable text
`Arrays.sort(a)`	sorts the array from small to big (changes it)
`Arrays.fill(a, v)`	sets every element to `v`
`Arrays.copyOf(a, n)`	a new array with the first `n` elements
`Arrays.equals(a, b)`	true if both arrays hold the same values
`Arrays.binarySearch(a, v)`	index of `v` in a sorted array

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] nums = {5, 2, 9, 1};
        Arrays.sort(nums);
        System.out.println(Arrays.toString(nums));
        System.out.println(Arrays.binarySearch(nums, 5));

        String[] names = {"Ravi", "Asha", "Meera"};
        Arrays.sort(names);
        System.out.println(Arrays.toString(names));

        int[] zeros = new int[4];
        Arrays.fill(zeros, 7);
        System.out.println(Arrays.toString(zeros));
    }
}

Output

[1, 2, 5, 9]
2
[Asha, Meera, Ravi]
[7, 7, 7, 7]

Copying an array the right way

b = a does not copy an array – both names point to the same lockers:

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] a = {1, 2, 3};
        int[] same = a;
        int[] copy = Arrays.copyOf(a, a.length);
        a[0] = 99;
        System.out.println(Arrays.toString(same));
        System.out.println(Arrays.toString(copy));
    }
}

Output

[99, 2, 3]
[1, 2, 3]

Common mistake: Changing a also changed same, because they are the same array. Use Arrays.copyOf to get a real, separate copy.