revision:
arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.
to declare an array, define the variable type with square brackets: String[] cars;
to insert values to it, we can use an array literal - place the values in a comma-separated list, inside curly braces: String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
to create an array of integers, you could write: int[] myNum = {10, 20, 30, 40};
an array element can be accessed by referring to the index number. Array indexes start with 0: [0] is the first element. [1] is the second element, etc.
example:
public class Main {
public static void main(String[] args) {
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
System.out.println(cars[0]); // Volvo
System.out.println(cars[2]); // Ford
}
}
To change the value of a specific element, refer to the index number.
example:
public class Main {
public static void main(String[] args) {
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
cars[0] = "Opel";
System.out.println(cars[0]); // Opel
}
}
To find out how many elements an array has, use the length property.
example:
public class Main {
public static void main(String[] args) {
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
System.out.println(cars.length); // 4
}
}
You can loop through the array elements with the for loop, and use the length property to specify how many times the loop should run.
example:
public class Main {
public static void main(String[] args) {
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
for (int i = 0; i < cars.length; i++) {
System.out.println(cars[i]); // Volvo BMW Ford Mazda
}
}
}
A "for-each" loop can be used exclusively to loop through elements in arrays.
syntax:
for (type variable : arrayname) {
...
}
example:
public class Main {
public static void main(String[] args) {
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
for (String i : cars) {
System.out.println(i); // Volvo BMW Ford Mazda
}
}
}
A multidimensional array is an array of arrays. To create a two-dimensional array, add each array within its own set of curly braces.
example:
public class Main {
public static void main(String[] args) {
int[][] myNumbers = { {1, 2, 3, 4}, {5, 6, 7} };
int x = myNumbers[1][2];
System.out.println(x); // 7
}
}
To access the elements of the myNumbers array, specify two indexes: one for the array, and one for the element inside that array. This example accesses the third element (2) in the second array (1) of myNumbers:
Also a for loop inside another for loop can be used to get the elements of a two-dimensional array (we still have to point to the two indexes).
example:
public class Main {
public static void main(String[] args) {
int[][] myNumbers = { {1, 2, 3, 4}, {5, 6, 7} };
for (int i = 0; i < myNumbers.length; ++i) {
for(int j = 0; j < myNumbers[i].length; ++j) {
System.out.println(myNumbers[i][j]); // 1 2 3 4 5 6 7
}
}
}
}