Running Java Programs Without a Full JDK: Understanding JRE and JVM

Introduction

When considering the execution of a Java program, it's a common question whether a full JDK (Java Development Kit) is necessary. The straightforward answer is that, in many cases, a Java Runtime Environment (JRE) is sufficient to run a Java program. This article will delve into the roles of JRE, JVM, and JDK, clarifying the scenario where a Java program can run without a full JDK.

Understanding JRE, JDK, and JVM

Java Runtime Environment (JRE) is a crucial component that includes the Java Virtual Machine (JVM) and a set of standard libraries necessary to run Java applications. Notably, the JRE does not include development tools, making it lighter and more suitable for run-time environments.

The Java Development Kit (JDK), on the other hand, is a comprehensive set of tools used by developers to create, compile, and run Java applications. It includes the JRE, but also adds development tools such as a compiler.

The Java Virtual Machine (JVM) serves as the engine that runs Java bytecode, translating it into machine code for the host system. This translation is essential for the cross-platform capability of Java.

Running Java Programs with JRE

For clients or customers, running a Java program typically requires only the JRE. The JRE provides the necessary libraries and components for the execution of Java applications. If a Java program is distributed as a standalone .jar (Java Archive) file, it can run on a system with only the JRE installed. This is because the JRE includes the JVM, which is responsible for interpreting and running the compiled Java bytecode.

However, for developers or programmers, the situation changes. Developers need a compiler to convert source code into bytecode. While the JRE includes a runtime compiler, the JDK includes this and more development tools. Therefore, developers need a full JDK to compile and run their Java programs.

Commercial Packaging Solutions

Certain commercial packaging solutions can package both the JRE and the application .jar file into a singleutable. For instance, InstallJ is one such tool that can bundle a JRE and a JAR into autable. However, these solutions come at a cost and may be expensive for small-scale projects.

For example, the author mentions considering InstallJ to run specific JARs on both Windows 10 and XP. The availability of other similar tools suggests that there is a market for such solutions, catering to developers who need to distribute their applications easily.

Best Practices for Distributing Java Applications

The current best practice for distributing Java applications is to include a compatible JRE with the application itself. This ensures that the application can run on any system where the JRE is present, regardless of the host system's configuration.

Tools like jlink and jpackage from the JDK can help create custom JRE images and native installers. These tools allow developers to package the necessary JRE alongside the application, ensuring that the program runs seamlessly across different operating systems without the need for additional installations.

In conclusion, while a full JDK is necessary for development purposes, a JRE is sufficient for running Java programs. Commercial solutions exist to simplify the distribution process, but for developers, integrating the necessary components with the application itself remains the most reliable method for cross-platform compatibility.