Null Check Analysis

Null dereferencing is one of the most frequent bugs in Java systems causing programs to crash due to the uncaught NullPointerException. Developers often fix this bug by introducing a guard (i.e., null check) on the potentially-null objects before using them. In this paper we investigate the null checks in 717 open-source Java systems to understand when and why developers introduce null checks. We find that 35 of the if-statements are null checks. A deeper investigation shows that 71 of the checked-for-null objects are returned from method calls. This indicates that null checks have a serious impact on performance and that developers introduce null checks when they use methods that return null.

Quo vadis Aethina tumida? Biology and control of small hive beetles

Small hive beetles (SHBs) are generalists native to sub-Saharan Africa and reproduce in association with honeybees, bumblebees, stingless bees, fruits and meat. The SHB has recently become an invasive species, and introductions have been recorded from America, Australia, Europe and Asia since 1996. hile SHBs are usually considered a minor pest in Africa, they can cause significant damage to social bee colonies in their new ranges. Potential reasons for differential impact include differences in bee behaviour, climate and release from natural enemies. Here, we provide an overview on biology, distribution, pest status, diagnosis, control and prevention to foster adequate mitigation and stimulate future research. SHBs have become a global threat to both apiculture and wild bee populations, but our knowledge of this pest is still limited, reating demand for more research in all areas of its biology.

Beautiful butterflies of the tropics, how to collect them,

Each plate accompanied by guard sheet with descriptive letterpress.

Fielding Yost with former players Donald Green, Maurice Crumpacker and Denny Clark at Portland, OR alumni event April 1923

[Alumnus caption: "A Reunion of the Old Guard The Coach with Three Old Pupils, Donald W. Green, '11; M.E. Crumpacker, '09 W. D. Clark, '07]

Le travail en Amérique avant et après Colomb,

Plates accompanied by guard sheets with descriptive letterpress.

Proceedings of the public meeting to review the status of the inexhaustible energy resources study.

Public meeting held at National Guard Heritage Gallery Auditorium, in Washington, D.C., May 18, 1977.

Investigation of extreme weather oil pollution response capabilities /

Prepared by Seaward International, Inc., under contract no. DOT-CG-80372-A.

Educational alternatives for boating safety programs /

Final report; May 1978.

Turkey,

Frontispiece accompanied by guard sheet with descriptive letterpress.

American waterfowl; their present situation and the outlook for their future,

Each plate accompanied by guard sheet with descriptive letterpress.

A survey,

Each plate accompanied by guard sheet with descriptive letterpress.

Epochs of Chinese & Japanese art : an outline history of East Asiatic design /

Preface includes biography of the author.

Splash and spray suppression: technological developments in the design and testing of spray reduction devices for heavy trucks. Report to Congress.

Mode of access: Internet.

Statistical evaluation of the effectiveness of Federal Motor Vehicle Safety Standard 214: Side Door Strength. Final report.

National Highway Traffic Safety Administration, Washington, D.C.

USCG group control and communications system study /

Final report; January 1979.