overview summary data structure is the organization of data in computer' memory or in disk file the correct choice of data structure allows major improvements in program efficiency examples of data structures are arraysstacksand linked lists an algorithm is procedure for carrying out particular task in javaan algorithm is usually implemented by class method many of the data structures and algorithms described in this book are most often used to build databases some data structures are used as programmer' toolsthey help execute an algorithm other data structures model real-world situationssuch as telephone lines running between cities database is unit of data storage composed of many similar records record often represents real-world objectsuch as an employee or car part record is divided into fields each field stores one characteristic of the object described by the record key is field in record that' used to carry out some operation on the data for examplepersonnel records might be sorted by lastname field database can be searched for all records whose key field has certain value this value is called search key questions these questions are intended as self-test for readers answers to the questions may be found in appendix in many data structures you can single recorditand it rearranging the contents of data structure into certain order is called