Writing Efficient Code

(in Java)

#### Looking things up

Don't ask arrays/lists to do "contains()"

Watch out for LinkedList.get(i).

Hashtables as functions

arrays as functions

boolean[] charIsSpecial = new boolean[255];
charIsSpecial['.'] = true;
charIsSpecial[';'] = true;

arrays allocate then ZERO all the memory; expensive.  Reuse arrays if you can.

#### Sorting

Insertion sort

Radix sort using hashtable

#### Java library stuff

Strings (+ operator)

make sure to close java sockets, files.

#### Input, Output

Used buffered IO

read all into memory if you can (unless really big)

#### Memory allocation

Arrays are initialized to 0

Don't forget to release memory (ptr=null)

#### Recursion

Useful but can be expensive as hell

#### Misc

Witchel asked about a loop that must only run for n seconds.  He was very
worried about a loop expr "while ((System.currentTimeInMillis()-start)>n*1000)"
or whatever.  I told him to use a boolean !done test and then launch a timeout
thread that sleeps n seconds and then sets done to true.