## Examples
### /com/in28minutes/java/arrays/ArrayExamples.java
```
package com.in28minutes.java.arrays;
import java.util.Arrays;
public class ArrayExamples {
public static void main(String[] args) {
// Declare an Array. All below ways are legal.
int marks[]; // Not Readable
int[] runs; // Not Readable
int[] temperatures;// Recommended
// Declaration of an Array should not include size.
// int values[5];//Compilation Error!
// Declaring 2D ArrayExamples
int[][] matrix1; // Recommended
int[] matrix2[]; // Legal but not readable. Avoid.
// Creating an array
marks = new int[5]; // 5 is size of array
// Size of an array is mandatory to create an array
// marks = new int[];//COMPILER ERROR
// Once An Array is created, its size cannot be changed.
// Declaring and creating an array in same line
int marks2[] = new int[5];
// new Arrays are alway initialized with default values
System.out.println(marks2[0]);// 0
// Default Values
// byte,short,int,long-0
// float,double-0.0
// boolean false
// object-null
// Assigning values to array
marks[0] = 25;
marks[1] = 30;
marks[2] = 50;
marks[3] = 10;
marks[4] = 5;
// ArrayOnHeap.xls
// Note : Index of an array runs from 0 to length - 1
// Declare, Create and Initialize Array on same line
int marks3[] = { 25, 30, 50, 10, 5 };
// Leaving additional comma is not a problem
int marks4[] = { 25, 30, 50, 10, 5, };
// Default Values in Array
// numbers - 0 floating point - 0.0 Objects - null
// Length of an array : Property length
int length = marks.length;
// Printing a value from array
System.out.println(marks[2]);
// Looping around an array - Enhanced for loop
for (int mark : marks) {
System.out.println(mark);
}
// Fill array with same default value
Arrays.fill(marks, 100); // All array values will be 100
// Access 10th element when array has only length 5
// Runtime Exception : ArrayIndexOutOfBoundsException
// System.out.println(marks[10]);
// String Array: similar to int array.
String[] daysOfWeek = { "Sunday", "Monday", "Tuesday", "Wednesday",
"Thursday", "Friday", "Saturday" };
// Array can contain only values of same type.
// COMPILE ERROR!!
// int marks4[] = {10,15.0}; //10 is int 15.0 is float
// Cross assigment of primitive arrays is ILLEGAL
int[] ints = new int[5];
short[] shorts = new short[5];
// ints = shorts;//COMPILER ERROR
// ints = (int[])shorts;//COMPILER ERROR
// 2D Arrays
int[][] matrix = { { 1, 2, 3 }, { 4, 5, 6 } };
int[][] matrixA = new int[5][6];
// First dimension is necessary to create a 2D Array
// Best way to visualize a 2D array is as an array of arrays
// ArrayOnHeap.xls
matrixA = new int[3][];// FINE
// matrixA = new int[][5];//COMPILER ERROR
// matrixA = new int[][];//COMPILER ERROR
// We can create a ragged 2D Array
matrixA[0] = new int[3];
matrixA[0] = new int[4];
matrixA[0] = new int[5];
// Above matrix has 2 rows 3 columns.
// Accessing an element from 2D array:
System.out.println(matrix[0][0]); // 1
System.out.println(matrix[1][2]); // 6
// Looping a 2D array:
for (int[] array : matrix) {
for (int number : array) {
System.out.println(number);
}
}
// Printing a 1D Array
int marks5[] = { 25, 30, 50, 10, 5 };
System.out.println(marks5); // [I@6db3f829
System.out.println(Arrays.toString(marks5));// [25, 30, 50, 10, 5]
// Printing a 2D Array
int[][] matrix3 = { { 1, 2, 3 }, { 4, 5, 6 } };
System.out.println(matrix3); // [[I@1d5a0305
System.out.println(Arrays.toString(matrix3));
// [[I@6db3f829, [I@42698403]
System.out.println(Arrays.deepToString(matrix3));
// [[1, 2, 3], [4, 5, 6]]
// matrix3[0] is a 1D Array
System.out.println(matrix3[0]);// [I@86c347
System.out.println(Arrays.toString(matrix3[0]));// [1, 2, 3]
// Comparing Arrays
int[] numbers1 = { 1, 2, 3 };
int[] numbers2 = { 4, 5, 6 };
System.out.println(Arrays.equals(numbers1, numbers2)); // false
int[] numbers3 = { 1, 2, 3 };
System.out.println(Arrays.equals(numbers1, numbers3)); // true
// Sorting An Array
int rollNos[] = { 12, 5, 7, 9 };
Arrays.sort(rollNos);
System.out.println(Arrays.toString(rollNos));// [5, 7, 9, 12]
// Array of Objects(ArrayOnHeap.xls)
Person[] persons = new Person[3];
// Creating an array of Persons creates
// 4 Reference Variables to Person
// It does not create the Person Objects
// ArrayOnHeap.xls
System.out.println(persons[0]);// null
// to assign objects we would need to create them
persons[0] = new Person();
persons[1] = new Person();
persons[2] = new Person();
// Other way
// How may objects are created?
Person[] personsAgain = { new Person(), new Person(), new Person() };
// How may objects are created?
Person[][] persons2D = { { new Person(), new Person(), new Person() },
{ new Person(), new Person() } };
}
}
class Person {
long ssn;
String name;
}
```