The dataset accompanying the paper "Demystifying and Assessing Code Understandability in Java Decompilation" is structured to facilitate a comprehensive analysis of code understandability in Java decompilation. The data is organized into two main directories: data/original and data/testset, representing the original dataset and the test set, respectively. Each directory encompasses three components. First, the code directory contains experimental data, including source code and corresponding decompiled code produced by three decompilers: CFR, Fernflower, and Jadx.