int[] ints;
double[] doubles;
boolean[] booleans;
String[] strings;

ints = new int[10];
doubles = new double[20];
booleans = new boolean[30];
strings = new String[40];

System.out.println(ints.length); // 10
System.out.println(doubles.length); // 20
System.out.println(booleans.length); // 30
System.out.println(strings.length); // 40

System.out.println(ints[0]); // 0
System.out.println(doubles[1]); // 0.0
System.out.println(booleans[2]); // false
System.out.println(strings[3]); // null

ints = new int[]{1, 2, 3};
doubles = new double[]{1};
booleans = new boolean[]{true, false};
strings = new String[]{"a", "b", "c"};

// i – index
for (int i = 0; i < ints.length; i++) {
    System.out.println(ints[i]);
}

// i – int
for (int i : ints) {
    System.out.println(i);
}

int[][] ints2d;
int[][][] ints3d;

ints2d = new int[10][20];
ints3d = new int[10][20][30];
System.out.println(ints2d[0]); // [I...
System.out.println(ints3d[0]); // [[I...

ints2d = new int[10][];
ints3d = new int[10][][];
System.out.println(ints2d[0]); // null
System.out.println(ints3d[0]); // null

for (int i = 0; i < ints2d.length; i++) {
    ints2d[i] = new int[i];
}

for (int[] row : ints2d) {
    System.out.println(row.length);
}

int[][] ints2d = new int[][]{{1, 2, 3}, {4, 5, 6}};
System.out.println(ints2d.length); // 2
System.out.println(ints2d[0].length); // 3
System.out.println(ints2d[1].length); // 3

int[][] ints2d = new int[][]{{1}, {2, 3}, null};
System.out.println(ints2d.length); // 3
System.out.println(ints2d[0].length); // 1
System.out.println(ints2d[1].length); // 2
System.out.println(ints2d[2]); // null

int[] as = new int[10];
int[] bs = as;
as[1] = 10;
System.out.println(as[1] + " " + bs[1]); // 10 10
System.out.println(as == bs); // true

bs = as;
as = new int[10];
as[1] = 20;
System.out.println(as[1] + " " + bs[1]); // 20 10
System.out.println(as == bs); // false

void fill(int[] ints, int value) {
    for (int i = 0; i < ints.length; i++) {
        ints[i] = value;
    }
}

fill(as, 100);
// 100 100 100
System.out.println(as[0] + " " + as[1] + " " + as[2]);

void referenceAsValue(int[] ints) {
    ints = new int[0];
}

bs = as;
referenceAsValue(as);
System.out.println(as == bs); // true

int[] create(int length, int value) {
    int[] ints = new int[length];
    fill(ints, value);
    return ints;
}

as = create(3, 123);
System.out.println(as[0] + " " + as[1] + " " + as[2]);
// 123 123 123

for (int i = 0; i < 10_000_000; i++) {
    as = new int[1000_000];
}
System.out.println("ok");

as = new int[]{0, 10, 20, 30, 40, 50};
bs = create(5, -1);
System.arraycopy(as, 2, bs, 1, 3);
// bs = {-1, 20, 30, 40, -1}

int[] as = new int[]{0, 10, 20, 30};
System.out.println(as);
    // [I@3834d63f
 
System.out.println(java.util.Arrays.toString(as));
    // [0, 10, 20, 30]
 
// import java.util.Arrays;
System.out.println(Arrays.toString(as));
    // [0, 10, 20, 30]

• lang – фундаментальные классы
  • String – строка
  • System – консольный ввод-вывод
  • ...
• util – вспомогательные классы
  • zip – поддержка Zip и GZip
  • Arrays – операции с массивами
  • Scanner – текстовый ввод
  • ...

• crypto – криптография
• ...

• Scanner(source) – получает данные из источника

• next() / nextInt() – следующий токен / число

// Стандартный ввод (stdin)
Scanner scanner = new Scanner(System.in);
System.out.print("Input two numbers: ");
int a = scanner.nextInt();
int b = scanner.nextInt();
System.out.println("Sum of numbers: " + (a + b));

• Шилдт Г. Java. Полное руководство (глава 3)
• Эккель Б. Философия Java (глава 16)

• Java Tutorial. Arrays
• The Java Language Specification. Arrays
• Baeldung Get Started with Java. Java Arrays