One dimensional Array
int [] scores; // Ok, recommended int scores []; // Ok but not recommended
Creation and assignment:
int [] scores = new int[3]; // Ok, always specify the size scores[0] = 84; // Ok scores[1] = 19; // Ok scores[2] = 25; // Ok // This compile, however it will throw // a runtime exception: "java.lang.ArrayIndexOutOfBoundsException": scores[3] = 96;
Short-cut assignment:
int [] scores = new int[] {84, 19, 25, 96}; // Ok
// This won't compile: never specify
// the array's size in a short-cut assignment:
int [] scores = new int[4] {84, 19, 25, 96};
Short-cut assignment without 'new':
int [] scores = {84, 19, 25, 96}; // Ok
An array of String:
String [] names = {"Tato", "Tuti", "Toto"}; // OK
An array of "Car" objects:
Car [] cars = {new Car("Mercedes"), new Car("Ferrari"), new Car("Renault")}; // Ok
Polymorphism: in this example "Ferrari" extends "Car":
Car [] cars = {new Car("Mercedes"), new Ferrari(), new Car("Renault")}; // OK, as "Ferrari" IS-A "Car"
An array which contains a primitive type can not be casted to an array which contains a different primitive type.
int[] scores; int[] scoresInt = new int[4]; long[] scoresLong = new long[4]; // Ok, as the variables 'scores' and 'scoresInt' have the same reference type: scores = scoresInt; // This won't compile, message: "incompatible types": scores = scoresLong;
An array which contains an Object type can be casted to an array which contains a different Object type if the condition 'IS-A' is fulfilled.
// In this example, "Horse" extends "Animal". Animal[] animals = new Horse[4]; // Ok as "Horse" IS-AN "Animal" Car[] cars = new Car[4]; animals = cars; // This won't compile as "Car" IS-NOT an "Animal"It is possible to cast an array into 'Object':
// Ok, as an "Array" IS-AN "Object":
Object myObj = new int[4]; // This won't compile as this array contains an array of primitive integers: Object[] myObj = new int[4]; // Ok, as this array contains an array of primitive integers' arrays: Object[] myObj = new int[3][2]; Object myObj = new String[4]; // Ok // Ok, as this array contains an array of String objects: Object[] myObj = new String[4]; int [][] scores; // Ok, 2 dimensionnals array int scores [][]; // Ok, 2 dimensionnals array, but not recommended int [] scores []; // Ok, 2 dimensionnals array, but not recommended int [][] teamsScores = new int[4][2]; // Ok Object myObj = teamsScores; // Ok int[][] scores = (int[][])myObj; // Ok int[] scores2 = (int[])myObj; // This won't compile, the variable 'myObj' has a reference to a 2 dimensional integer array
Multi-dimensional Array
Declaration:
int [][] scores; // Ok, 2 dimensional array int scores [][]; // Ok, 2 dimensionnals array, but not recommended int [] scores []; // Ok, 2 dimensionnals array, but not recommended
Creation and assignment
int [][] myArray = new int[2][]; // Ok, you do not need to specify the size of the second index myArray[0] = new int[1]; // Ok myArray[0][0] = 54; // Ok myArray[1] = new int[2]; // Ok myArray[1][0] = 83; // Ok myArray[1][1] = 92; // Ok int [][] myArray = new int[2][2]; // Ok, if you specify the second index then you do not need to create new array object for each index myArray[0][0] = 54; // Ok myArray[1][0] = 83; // Ok myArray[1][1] = 92; // Ok
Shortcut assignment:
int [][] myArray = new int [][] {{54}, {83, 92}}; // Ok
Shortcut assignment without 'new':
int [][] myArray = {{54}, {83, 92}}; // Ok
