NPEFix: Automatic Runtime Repair of Null Pointer Exceptions in Java

Null pointer exceptions, also known as null dereferences are the number one exceptions in the field. In this paper, we propose 9 alternative execution semantics when a null pointer exception is about to happen. We implement those alternative execution strategies using code transformation in a tool called NPEfix. We evaluate our prototype implementation on 11 field null dereference bugs and 519 seeded failures and show that NPEfix is able to repair at runtime 10/11 and 318/519 failures

Fighting Risky Population Synchronization: Desynchronization and Stabilization in Spatially Structured Ecological Systems

Population synchronization exists ubiquitously in ecological systems, of which the underlying causes and the roles in species extinction remain a perplexing puzzle. It is generally believed that the coherence of population dynamics is detrimental and regarded as a major cause of global extinction. A central but unsolved question in ecology of great importance for conservation and biological control is how to destroy the pernicious coherent structures. Here, a top-down approach is adopted to tackle the challenge. A feedback strategy accordingly is applied to stabilize the metacommunity, i.e., to reduce excessive metapopulation fluctuations by means of introducing or removing a planned number of individuals. As a result, the feedback desynchronizes correlated population oscillations, giving rise to either complex asynchronous traveling waves or "amplitude death"; cessation of all individual population cycles. Together with the construction of corridors, my method may provide an efficient way to protect those species threatened as a result of, e.g. habitat fragmentation. I anticipate my essay provides a general mechanism against widespread harmful synchronization in physical and biological systems, for example, for developing a "brain anti-pacemaker" for neurological diseases such as Parkinson's disease and epilepsy closely linked to pathologically synchronized neuronal discharges

Homologous self-organising scale-invariant properties characterise long range species spread and cancer invasion

The invariance of some system properties over a range of temporal and/or spatial scales is an attribute of many processes in nature1, often characterised by power law functions and fractal geometry2. In particular, there is growing consensus in that fat-tailed functions like the power law adequately describe long-distance dispersal (LDD) spread of organisms 3,4. Here we show that the spatial spread of individuals governed by a power law dispersal function is represented by a clear and unique signature, characterised by two properties: A fractal geometry of the boundaries of patches generated by dispersal with a fractal dimension D displaying universal features, and a disrupted patch size distribution characterised by two different power laws. Analysing patterns obtained by simulations and real patterns from species dispersal and cell spread in cancer invasion we show that both pattern properties are a direct result of LDD and localised dispersal and recruitment, reflecting population self-organisation