Java summary: Arrays



Declaring an array

  • Example: int[] a;
  • Is a reference, like an object

Array allocation

  • Allocating memory for an array
    • Example: a = new int[100]; (fixed size)
    • an array is an object
  • all elements are set to zero (numeric), null (object types) or false (boolean)
  • Anonymous array -- Example: int[] a = new int[] {1,2}; -> array of length 2
    • String[] words = new String[]{"bla", "blo", "bli"};

Accessing elements

with Subscripts
-- Example: a[i]
  • Subscript ranges always start at zero
  • Java always checks Subscript legality, between 0 and size. If not, Java throws ArrayIndexOutOfBoundsException

    • Array length

    -- Example: a.length
    • typical statement for looping over an array
    for (int i = 0;i < a.length;i++){
       a[i]=10;
    }

  • Two-dimensional arrays

    • int[][] a = new int[2][3];  // Two rows and three columns.
    • a[1][1] = 5;

  •  Vectors

  • For dynamically extendable arrays: use vectors of the java.util package.

  • vector<int> v = new vector<int>();
  • v.add(2);
  • for(int i = 0;i < v.size(); i++){
  •   System.out.println("Element " + i + "=" + v.get(i));
  • }
    		•