Java streams enable an easy-to-use functional-like programming style that transparently supports parallel execution. This paper presents an approach that improves the performance of stream-based Java applications. The approach enables the effective usage of Java for HPC applications, due to data locality improvements (i.e., support for efficient data layouts), without losing the object-oriented view of data in the code. The approach extends the Java collections API to hide additional details concerning the data layout, enabling the transparent use of more memory-friendly data layouts. The enhanced Java Collection API enables an easy adaptation of existing Java codes making those Java codes suitable for HPC. Performance results show that improving the data locality can provide a two-fold performance gain in sequential stream applications, which translated into a similar gain over parallel stream implementations. Moreover, the performance is comparable to similar C implementations using OpenMP.