There are two uses for the term "double array". The first indicates that an array is made up of data elements of the scalar type double, a kind of floating point number. The second use describes an array that is two-dimensional (2D) or multidimensional. Multidimensional arrays have more than one index into the memory locations of the data, meaning each element within the double array is actually the start of another array. In object oriented languages, a double array also can indicate an array that contains elements of the class double, instead of the scalar type.
Not all computer programming languages have a data type known as a double. In general, however, it is a floating point representation of a number that takes up twice, or double, the amount of space that a single precision number occupies. These numbers can hold remarkably high values that are usually expressed with exponents. Most computer hardware uses 64 bits to represent a double, meaning a double array will occupy 8 bytes in memory for each element, although some hardware uses 128 bits or more for a double precision data type.
Many object oriented programming languages have wrapper classes for scalar data types, allowing them to be treated like any other class or object. A double array can contain these objects instead, in which case the array will function like an array of instanced classes. This can sometimes be useful for some network situations in which serialization is an issue or in multithreaded applications where synchronization is important.
When referring to a multidimensional array, a double array usually indicates an array that has two sets of indices. A one-dimensional array is simply a list of similar data types that are all aligned consecutively in computer memory, with the location of each separate data cell being numbered sequentially upwards starting at zero. The number that corresponds to the location of the data within the array is known as its index, and the data at the index are called the data element, or just element.
A double array is basically a single-dimensional array in which each index is actually the first index of another single-dimensional array. One way to visualize a double array is as a grid, or a piece of graph paper. The first index in the array would refer to which column in the grid is being referenced, while the second index would indicate what row within that column is being accessed.