This paper concerns itself with possibilities of declarative programming in the new version of Java 8 language, specifically using elements adopted from the domain of functional programming languages: function as a value and lazy streams of data. The goal of this paper is to demonstrate possibilities of declarative programming using these elements, analyze its implementation and design own extensions. The contribution lies particularly in showing possibilities of the new elements, implementation analysis and design of a new functionality. The output can be used by a Czech reader, who is at least slightly advanced in the field of information technologies. The paper is divided into a theoretical and practical parts. Theoretical part is covered by chapters 3-8. Theoretical part describes motivation for introduction of the new elements, describes functional programming and its basic principles, then it shows basic principles of the newly introducted elements and ends with the description of the java.util.stream package. Pactical part is covered by chapters 9 and 10. Practical part concerns with stream oper-ations and extension design of existing functionality.