Arrays

From Suhrid.net Wiki
Revision as of 10:25, 28 June 2011 by Suhridk (talk | contribs)
Jump to navigationJump to search

Introduction

  • Arrays store multiple variables of the same type.
  • The array itself is always an object on the heap (even if it is storing primitive elements).
  • Arrays can be multi-dimensional.
  • Think of a multi-dimensional array as an array of arrays.

Declaring

  • int[] scores; (Preferred) or int scores[]; (Legal, but bad)
  • String[] names;
  • int[][] matrix;

Constructing

  • int[] scores = new int[10];
  • This will create a new array object on the heap. All the int values will be assigned their default values, Object references will be assigned null.
  • The array size must be present, when there is no initializer.
  • double[] rates = new double[]; //illegal
  • Thread[] pool = new Thread[10]; //No thread objects are created here, only the array object to hold ten thread references is created.
  • int[][] matrix = new int[5][];
  • Only the size of the array needs to be specified - in this case 5 says that matrix 2-D array can store 5 1-D array objects. So only the 5 is sufficient to be specified.
  • Of course we can also specify both dimensions like int[][] matrix = new int[3][2]; Which menas that matrix can store 3 1-D arrays each of length 2.

Initializing

  • Initializing means assigning values to the elements of the array.
  • Initializing can be done after the array is declared and constructed.
  • Initializing can also be combined along with the array declaration and construction.
String[] names; //Declare
names = new String[3]; //Construct
//Initialize
names[0] = "A";
names[1] = "B";
names[2] = "C";

//All in one
String[] names = new String[] {"A", "B", "C"};

//Multi-dimensional - initing a 3x3 int array
int[][] matrix = { {1,2,3}, {4,5,6}, {7,8,9} };
Illegal Legal
int[5] scores; //No size in LHS.
int[] scores = new int[]; //No size specified;