This chapter investigates the evolution in time of the number of lines of the Java source code of the Java Development Kit (JDK). We show that the rank-size distributions of the JDK source files developed characteristic evolutionary patterns during the last fifteen years, such as parabolic fractal distributions, and a sigmoid shape of the cumulated lines of code. In order to explain the emergence of these patterns, we propose here to consider the constructal tree-shaped invasion of a territory combined with the constructal rank-size distribution of a growing population as the mechanism potentially generating a wide variety of population distributions. In the case of the JDK, the functional scope addressed by the successive versions of the platform, assimilated to a functional space to invade, continuously increased in time. The development of the JDK‘s functional packages hierarchy is interpreted as the constructal tree-structure followed by the invasive flow. We propose in conclusion to consider the Constructal Law as the main driver behind software evolution.