package com.nishith.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 always 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;

}