Arrays
Create, loop over, sort and copy arrays.
An array stores a fixed number of values of the same type. Its length is set when it is created and cannot change afterwards.
public class Main {
public static void main(String[] args) {
int[] marks = {78, 92, 65, 88};
System.out.println(marks[0]);
System.out.println(marks.length);
marks[2] = 70;
int total = 0;
for (int m : marks) {
total += m;
}
System.out.println("Average: " + (double) total / marks.length);
}
}Output
78 4 Average: 82.0
Creating an empty array
new int[5] creates an array of five zeros. Arrays of objects, such as String, start filled with null.
public class Main {
public static void main(String[] args) {
int[] squares = new int[5];
for (int i = 0; i < squares.length; i++) {
squares[i] = (i + 1) * (i + 1);
}
String[] names = new String[2];
System.out.println(squares[4]);
System.out.println(names[0]);
}
}Output
25 null
The Arrays helper class
java.util.Arrays has ready-made methods for printing, sorting, searching and copying.
import java.util.Arrays;
public class Main {
public static void main(String[] args) {
int[] nums = {42, 7, 19, 88, 3};
System.out.println(Arrays.toString(nums));
Arrays.sort(nums);
System.out.println(Arrays.toString(nums));
System.out.println(Arrays.binarySearch(nums, 42));
int[] firstThree = Arrays.copyOf(nums, 3);
System.out.println(Arrays.toString(firstThree));
}
}Output
[42, 7, 19, 88, 3] [3, 7, 19, 42, 88] 3 [3, 7, 19]
Two-dimensional arrays
public class Main {
public static void main(String[] args) {
int[][] table = new int[3][3];
for (int r = 0; r < 3; r++) {
for (int c = 0; c < 3; c++) {
table[r][c] = (r + 1) * (c + 1);
}
}
for (int[] row : table) {
for (int value : row) {
System.out.printf("%3d", value);
}
System.out.println();
}
}
}Output
1 2 3 2 4 6 3 6 9
Accessing an index outside the array, such as marks[4] above, throws an ArrayIndexOutOfBoundsException.