ArraysDemoTest.java

package cse2010.arrays;

import org.junit.jupiter.api.Test;

import java.util.Arrays;
import java.util.Comparator;
import java.util.stream.Collectors;

import static org.junit.jupiter.api.Assertions.*;

public class ArrayDemo2Test {

    int as[] = { 1, 3, 5, 7, 9 };
    int bs[] = { 1, 3, 5, 7, 9 };

    @Test
    void streamTest() {
        int total = Arrays.stream(as).sum();

        assertEquals(25, total);
    }

    @Test
    void arrayEquals_WrongWay() {

        assertFalse(as.equals(bs));
    }

    @Test
    void arrayEquals_RightWay() {

        assertTrue(Arrays.equals(as, bs));
        assertArrayEquals(as, bs);
    }

    @Test
    void array_filling() {
        int[] expected = { 777, 777, 777, 777, 777 };

        Arrays.fill(as, 777);

        assertTrue(Arrays.equals(as, expected));
    }

    @Test
    void array_filling2() {

        Arrays.fill(as, 1, 3, 0);

        System.out.println(as.toString()); // maybe not what you want
        System.out.println(Arrays.toString(as));
    }

    @Test
    void arrays_toString() {
        for (int i = 0; i < as.length; i++)
            System.out.println(as[i]);
        // is equivalent to: (for-each loop)
        for (int a : as) System.out.println(a);

        System.out.println(Arrays.toString(as));
    }

    @Test
    void array_System_arraycopy() {
        int[] as = { 2, 4, 6, 8, 10 };

        System.out.println(Arrays.toString(as));
        System.out.println(Arrays.toString(bs));
        System.arraycopy(as, 1, bs, 1, 3);
        System.out.println(Arrays.toString(bs));
    }

    @Test
    void array_copyOf() {

        int[] ys = Arrays.copyOf(as, 10);

        System.out.println(Arrays.toString(ys));
        System.out.println(Arrays.toString(as));
    }

    @Test
    void array_copyOfRange() {

        int ys[] = Arrays.copyOfRange(as, 1, 4);

        System.out.println(Arrays.toString(ys));
        System.out.println(Arrays.toString(as));
    }

    @Test
    void arrays_setAll() {
        int[] ints = new int[10];

        Arrays.setAll(ints, i -> i * i);

        System.out.println(Arrays.toString(ints));
    }

    @Test
    void array_deepToString() {

        int[][] two = { { 1, 2, 3 }, { 4, 5, 6 } };

        System.out.println(Arrays.toString(two)); // oops!
        System.out.println(Arrays.deepToString(two));
    }

    @Test
    void array_sort() {
        int xs[] = { 9, 7, 5, 3, 1 };

        Arrays.sort(xs);    // quick sort

        System.out.println(Arrays.toString(xs));
    }

    private void reset(Integer[] xs) {
        Arrays.setAll(xs, i -> i);
    }

    @Test
    void array_sortWithComparator() {
        Integer[] xs = new Integer[10];

        reset(xs);
        System.out.println(Arrays.toString(xs));

        Arrays.sort(xs);
        System.out.println(Arrays.toString(xs));

        reset(xs);
        Arrays.sort(xs, (o1, o2) -> o1 - o2); // ascending order
        System.out.println(Arrays.toString(xs));

        reset(xs);
        Arrays.sort(xs, (o1, o2) -> o2 - o1); // descending order
        System.out.println(Arrays.toString(xs));

        reset(xs);
        Arrays.sort(xs, Comparator.naturalOrder());
        System.out.println(Arrays.toString(xs));

        reset(xs);
        Arrays.sort(xs, Comparator.reverseOrder());
        System.out.println(Arrays.toString(xs));

        reset(xs);
        Integer[] integers = Arrays.stream(xs).toArray(Integer[]::new);
        System.out.println(Arrays.toString(integers));
    }

    @Test
    void miscellaneous1() {

        int[][] as = new int[2][3];
        for (int i = 0; i < as.length; i++) {
            final int k = i;
            Arrays.setAll(as[i], j -> k + j);
        }
        System.out.println(Arrays.deepToString(as));

        int[][] bs = new int[2][];
        Arrays.setAll(bs, i -> new int[3]);
        System.out.println(Arrays.deepToString(bs));
    }

    @Test
    void miscellaneous2() {
        int[][] arrays = { { 1, 2, 3 }, { 4, 5, 6 } };

        Arrays.stream(arrays)
              .forEach(e -> System.out.println(Arrays.toString(e)));

        System.out.println("---------------------------");

        String values = Arrays.stream(arrays)
                              .map(Arrays::toString)
                              .collect(Collectors.joining("\n"));

        System.out.println(values);
    }
}