Arrays

Arrays

• Like classes, arrays are also sequences of memory boxes. However
  • Classes have named memory boxes (mapped variable names to memory).
  • Class boxes can store different types.
  • Arrays have numbered memory boxes (accessible by index). Arrays do not have methods
  • Array boxes must store the same variable type.
• Any array has a fixed length

Array Creation

• There are three ways to create an array:

x = new int[3];
int[] y = new int[]{1, 2, 3, 4, 5};
int[] z = {9, 10, 11, 12, 13}

• First notation creates an array of length 3 and each memory box is filled with default value 0.
• Second notation creates an array with the size needed to store the specified values.
• Third notation declares and creates z, but omits the use of new.

Array Access and Modification

• We can access array elements using index notation like in python.
  • However, Java does not support negative indexing.
• Java also has as a method System.arraycopy that copies one section of one array over to a same-length section in another array. Five parameters ar etaken
  • The source array
  • Starting index in the source array
  • The destination array
  • Starting index in the destination array
  • How many items to copy.

int[] x = {1,2,3,4,5};
int[] y = new int[5];
System.arraycopy(x, 2, y, 3, 2);
Arrays.toString(y);

[0, 0, 0, 3, 4]

• We may also use a loop to copy over array elements. However, if we run out of index out of bounds errors, Java only catches them at runtime, and not compilation.

2D Java Arrays

• 2D arrays in Java are just arrays of arrays.
• However, each element in the parent array doesn’t store the memory boxes of the array, rather, it stores an array reference to the memory location of the child arrays.