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The base Java programming environment has been around since the late 1990s. It is composed of the Java language and the supporting runtime, the Java Virtual Machine (JVM). The third leg—the Java ecosystem beyond the standard library that ships with Java—is provided by third parties, such as open-source projects and Java technology vendors. At the time that Java was initially developed, this split was considered novel, but trends in software development in the intervening years have made it more commonplace. Notably, Microsoft’s .NET environment, announced a few years after Java, adopted a very similar approach to platform architecture. One important difference between Microsoft’s .NET platform and Java is that Java was always conceived as a relatively open ecosystem of multiple vendors, albeit led by a steward who owns the technology. Throughout Java’s history, these vendors have both cooperated and competed on aspects of Java technology. One of the main reasons for Java’s success is that this ecosystem is a standardized environment. This means there are specifications for the technologies that comprise the environment. These standards give the developer and consumer confidence that the technology will be compatible with other components, even if they come from a different technology vendor. The current steward of Java is Oracle Corporation (which acquired Sun Microsystems, the originator of Java). Other corporations, such as IBM, Red Hat, Amazon, Microsoft, SAP, Azul Systems, and Bellsoft, are also involved in producing implementations of standardized Java technologies. Java originally comprised several different, but related, environments and specifications, such as Java Mobile Edition (Java ME),1 Java Standard Edition (Java SE), and Java Enterprise Edition (Java EE).2 In this book, we’ll only cover Java SE, version 25, with some historical notes related to when certain features were introduced into the platform. Generally speaking, if someone says “Java” without any further clarification, they mean Java SE. We will have more to say about standardization later, so let’s move on to discuss the Java language and JVM as separate but related concepts.