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Arrays

By · Reviewed & last updated · Part of Java Tutorial

Java arrays are fixed-length, zero-indexed, and covariant. The modern way to work with them: java.util.Arrays for sort/fill/binarySearch, streams for transforms, List.of() when you don’t need mutability.

Arrays the way you actually use them

EXAMPLE
import java.util.Arrays;
import java.util.stream.IntStream;

public class ArrayDemo {
    public static void main(String[] args) {
        // 1) Declaration
        int[]     a = new int[5];                   // {0,0,0,0,0}
        int[]     b = { 1, 2, 3, 4, 5 };
        String[]  c = new String[]{ "a", "b" };
        int[][]   m = { { 1, 2 }, { 3, 4 } };       // 2-D — array of arrays

        // 2) Length
        System.out.println(b.length);

        // 3) Iterate
        for (int x : b) System.out.println(x);
        for (int i = 0; i < b.length; i++) System.out.println(i + "=" + b[i]);

        // 4) Arrays utility methods
        Arrays.sort(b);                              // in-place
        int idx = Arrays.binarySearch(b, 3);
        Arrays.fill(a, 1);                           // {1,1,1,1,1}
        int[] copy   = Arrays.copyOf(b, 10);          // size 10, padded with 0
        int[] slice  = Arrays.copyOfRange(b, 1, 4);   // [b[1], b[2], b[3]]
        System.out.println(Arrays.toString(b));
        System.out.println(Arrays.deepToString(m));

        // 5) Streams — sums, max, filters
        int total = Arrays.stream(b).sum();
        int max   = Arrays.stream(b).max().orElseThrow();
        int[] evens = Arrays.stream(b).filter(x -> x % 2 == 0).toArray();

        // 6) Build with IntStream
        int[] zero99 = IntStream.range(0, 100).toArray();
        int[] squares = IntStream.rangeClosed(1, 10).map(x -> x * x).toArray();

        // 7) Compare — use Arrays.equals, NOT ==
        int[] x = { 1, 2, 3 };
        int[] y = { 1, 2, 3 };
        System.out.println(x == y);                  // false — different objects
        System.out.println(Arrays.equals(x, y));     // true
        System.out.println(Arrays.deepEquals(m, m)); // true

        // 8) Convert to / from List
        var list = Arrays.asList("a", "b", "c");
        String[] back = list.toArray(new String[0]);

        // 9) Prefer List.of for immutable + clearer APIs
        var ro = List.of(1, 2, 3);                   // immutable
    }
}

Why it matters

List<T> beats T[] in modern Java. Arrays survive for performance hot paths, JNI, and varargs — everywhere else, List and Stream are clearer.

Tip: Tweak the snippet with Try it Yourself », then sit the quiz at the bottom of the page.

Example

Example
int[] nums = {1, 2, 3, 4};
for (int n : nums) System.out.println(n);
System.out.println(nums.length);
Try it Yourself »

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