Deep Java

Java Runtime Environment (JRE) Explained: What It Is, How It Works, and How to Install It

Java Fundamentals
目次

1. What Is Java Runtime (JRE)?

Java Runtime Environment (JRE) is an essential component required to run Java applications. However, many people may wonder, “I’ve heard the name, but what does it actually do?” or “What happens if I don’t install JRE?”

Java technology is used behind the scenes in personal computers, business systems, and even in some home appliances and smartphone applications. To run these Java-based applications correctly, JRE is absolutely necessary.

In this article, we will carefully explain Java Runtime (JRE) from the basics. It is designed to be useful for a wide range of readers—from beginners who wonder “What’s the difference between JRE and JDK?” or “Do I need JRE on my computer?”, to engineers who need practical knowledge for troubleshooting in real-world environments.

Let’s start by looking at an overview of JRE and its role.

2. Basics of Java Runtime Environment (JRE)

Java Runtime Environment (JRE) is a “runtime environment” required to execute applications written in Java on a computer or server. JRE translates Java program instructions into a form that the computer can understand and provides the foundation needed to run applications smoothly.

JRE consists of several key components.

  • JVM (Java Virtual Machine)
    JVM, also known as the Java Virtual Machine, is the mechanism that actually executes Java programs (bytecode). Thanks to JVM, Java applications can run consistently across different operating systems such as Windows, macOS, and Linux.
  • Libraries
    Java standard libraries (class libraries) provide commonly used functionality such as string manipulation, network communication, and date handling. These libraries are included in JRE and can be easily called from Java programs.
  • Class Loader and Supporting Tools
    The class loader loads the necessary components (class files) of a Java program as needed. This allows programs to run efficiently and securely.

JRE is a runtime-only environment and does not include development tools such as editors or compilers. In other words, JRE is a package designed for “running” Java applications, not for “creating” them.

In this way, JRE can be described as an indispensable foundation for running Java programs reliably across different environments. In the next section, we will explain the differences between JRE and the similarly named “JDK” and “JVM.”

3. Differences Between JRE, JDK, and JVM — and How to Choose

One of the most common sources of confusion in Java-related terminology is the difference between “JRE,” “JDK,” and “JVM.” Here, we will organize their roles and relationships and explain which one you should choose.

JRE (Java Runtime Environment)

JRE is an environment for “running” Java applications. As explained earlier, it includes JVM and standard libraries required to execute applications. It is the package needed by Java application users.

JDK (Java Development Kit)

JDK is an environment for “developing” Java applications. It includes JRE and additional tools such as the Java compiler (javac) and debuggers. Anyone who wants to create Java applications must install JDK.

JVM (Java Virtual Machine)

JVM is one of the core components of JRE. It converts Java bytecode into machine code for each operating system and executes it. Because different JVMs exist for different OSes, Java is known as a language that “runs the same way everywhere.”

Illustrative Relationship

  • JDK (Development Kit)
    • JRE (Runtime Environment)
      • JVM (Virtual Machine)

Which One Should You Choose? (Quick Guide by Use Case)

  • Just running Java applications → JRE is sufficient
  • Developing or building Java applications → JDK is required (includes JRE)

Recent Java Trends: End of Standalone JRE Distribution

In the past, JRE could be downloaded separately. However, in recent years, installing JDK automatically includes JRE, and standalone JRE distributions have been discontinued in many versions. As a result, the need to install only JRE has significantly decreased.

Additionally, the use of Java applets in web browsers has declined, further reducing situations where standalone JRE is required.

In summary, the correct choice depends on your purpose. Consider how you intend to use Java and select the appropriate environment accordingly.

4. Choosing and Checking the JRE Version

Java Runtime Environment (JRE) comes in various versions and builds. This section explains how to choose the appropriate version and how to check which JRE is installed on your system.

Differences Between 32-bit and 64-bit Versions

JRE is available in both 32-bit and 64-bit versions.
Most modern computers and operating systems support 64-bit architecture, so in general, it is recommended to choose the 64-bit version unless there is a specific reason not to.

However, some legacy applications or systems may only work correctly with the 32-bit version, so always check the requirements of the Java application you intend to use.

  • On Windows: You can check via “Control Panel” → “Java” → “Java” tab
  • On macOS: Only 64-bit versions are generally provided

Command to Check JRE Version (Windows / macOS / Linux)

Open a command prompt or terminal and enter the following command:

java -version

Example output:

java version "1.8.0_391"
Java(TM) SE Runtime Environment (build 1.8.0_391-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.391-b13, mixed mode)

From this output, you can identify the installed JRE version and whether it is 32-bit or 64-bit.

Which Version Should You Use? — Practical Guidelines

  • The latest stable version is generally recommended, but enterprise or mission-critical systems may require a specific version.
  • Older versions that are no longer supported (such as Java 6 or 7) pose serious security risks and should be avoided.
  • If multiple Java versions are required, careful configuration of environment variables and PATH settings is essential.

Choosing the correct JRE version directly affects application stability and security. If unsure, selecting the latest LTS (Long-Term Support) version in 64-bit is usually the safest choice.

5. Downloading and Installing JRE (With Illustrated Guidance)

Installing JRE (Java Runtime Environment) is not difficult, but procedures may vary depending on the operating system. This section explains major distribution sources and step-by-step installation methods for Windows, macOS, and Linux.

Main Distribution Sources and Their Differences

  • Oracle Official Website
    The most standard and reliable distribution source, widely used by both enterprises and individuals. Note that some versions require a commercial license for business use.
  • OpenJDK (Open-Source Version)
    A free and open-source Java runtime environment. Many Linux distributions use OpenJDK as the default. Compatibility and update frequency are generally sufficient.
  • Other Distributions (AdoptOpenJDK, Amazon Corretto, etc.)
    These are increasingly chosen depending on corporate policies or use cases. Most are based on OpenJDK but may include additional support or optimizations.

Installation Steps on Windows

  1. Access the Oracle official site or an OpenJDK distribution page
  2. Download the installer matching your OS and architecture (32-bit or 64-bit)
  3. Double-click the downloaded installer
  4. Follow the on-screen instructions and proceed with “Next” → “Install”
  5. After installation, open Command Prompt and run java -version to verify

Installation Steps on macOS

  1. Using Homebrew (a package manager for macOS) is recommended
  2. Enter the following command in Terminal:
brew install openjdk
  1. If instructions for symbolic links or PATH configuration appear, follow them
  2. Run java -version in Terminal to confirm installation

Installation Steps on Linux

  • Ubuntu:
sudo apt update
sudo apt install openjdk-17-jre
  • CentOS / RHEL:
sudo yum install java-17-openjdk

After installation, verify with java -version.

Important Notes During Installation

  • If multiple Java versions coexist, you must explicitly specify which version is used via PATH or environment variables.
  • If prompted to remove older JRE versions, uninstalling them is recommended for security reasons.

6. Updating and Uninstalling JRE: Procedures and Precautions

JRE (Java Runtime Environment) requires ongoing maintenance. Regular updates and removal of unnecessary versions are essential for security and stable operation.

How to Update JRE

  • Windows
    When JRE is installed, automatic updates are usually enabled by default. You will be notified when a new version is available. For manual updates, download the latest version from the Oracle or OpenJDK website and install it over the existing version.
  • macOS
    If installed via Homebrew, run the following commands:
brew update
brew upgrade openjdk
  • Linux
    Use the package manager for your distribution. Example:
sudo apt update
sudo apt upgrade openjdk-17-jre

How to Uninstall Older Versions

  • Windows
    Open “Control Panel” → “Uninstall a program,” select the unnecessary Java version, and uninstall it. Remove older unused versions whenever possible.
  • macOS
    Manual uninstallation requires deleting Java-related directories. The exact steps depend on how Java was installed, so consult official documentation.
  • Linux
    Use the package manager. Example for Ubuntu:
sudo apt remove openjdk-17-jre

Precautions When Updating or Removing JRE

  • Multiple Java versions can cause application conflicts. Regularly remove unused versions.
  • Leaving outdated JRE versions installed increases security risks due to known vulnerabilities.
  • In corporate environments, always confirm supported versions before updating or removing Java.

Regular JRE maintenance is a fundamental requirement for secure and stable Java application usage. The next section will introduce common problems and their solutions.

7. Common Problems and How to Fix Them

When using Java Runtime Environment (JRE), it is not uncommon to encounter unexpected issues or errors. This section introduces frequently occurring problems and their practical solutions.

“Java Not Found” or “Java Is Not Installed” Error

This error often occurs when Java is not installed correctly or when the installation path is not recognized by the system.

  • Solutions
  1. Check whether Java is installed by running the java -version command.
  2. If Java is not installed, reinstall JRE.
  3. If Java is installed, verify that the environment variable (PATH) is set correctly and adjust it if necessary.

Application Malfunctions Due to Version Mismatch

Some Java applications require a specific JRE version. If the installed version does not match the requirement, the application may fail to start or produce errors.

  • Solutions
  1. Check the application’s system requirements and install the required JRE version.
  2. If multiple JRE versions are installed, explicitly specify the preferred version using the PATH environment variable.
  3. If the error message specifies a required version, follow the instructions provided.

Errors Caused by Incorrect Environment Variable Settings

Especially on Windows and Linux, if the path to the Java executable (java.exe) is not properly set in the PATH environment variable, Java commands will not be recognized.

  • Solutions
  1. Add the Java installation directory (e.g., C:\Program Files\Java\jdk-17\bin) to the PATH variable.
  2. Restart the command prompt or terminal and verify with java -version.

Other Common Issues and Fixes

  • Security warnings due to leftover old JRE versions
    → Uninstall unnecessary Java versions via Control Panel or package managers.
  • Changes not reflected after installation
    → Restart the OS or reopen the command prompt/terminal.
  • Conflicts between 32-bit and 64-bit versions
    → Install and enable only the version that matches your OS and application requirements.

If problems persist, consult official documentation, application FAQs, or community forums for additional support.

8. Java Runtime Alternatives and Latest Trends

In recent years, Java runtime environments have diversified and evolved significantly. Beyond Oracle’s offerings, many open-source and enterprise-focused distributions are now available. This section introduces alternatives to JRE and the latest industry trends.

Major Alternative Runtime Distributions

  • OpenJDK
    An open-source Java runtime with high compatibility with Oracle JRE. It is the default choice for many Linux distributions and is free with strong community support.
  • AdoptOpenJDK (now Adoptium)
    A trusted OpenJDK build widely used in enterprise environments. It is free and offers reliable long-term support.
  • Amazon Corretto
    An OpenJDK-based distribution provided by Amazon. It includes long-term support (LTS) and is recommended for AWS environments.
  • Others (Zulu, Red Hat OpenJDK, SAP SapMachine, etc.)
    These distributions offer different support models and optimizations depending on enterprise needs.

Recent Java Trends: End of Standalone JRE and Modularization

  • End of Standalone JRE Distribution
    Starting with Java 11, Oracle discontinued standalone JRE distributions. JRE is now included within JDK, shifting management toward a unified JDK-based approach.
  • Java Modularization (Project Jigsaw)
    Since Java 9, the module system allows developers to build runtime environments using only required components, resulting in lighter and more secure applications.
  • LTS (Long-Term Support) Versions as the Standard
    Java releases new versions every six months, but in production environments, LTS versions (e.g., Java 8, 11, 17, 21) are generally preferred for stability and extended support.

Future Outlook and Selection Guidelines

  • For individuals or small projects, free OpenJDK-based distributions are usually sufficient.
  • For enterprises or large-scale systems, compare commercial support options and support lifecycles.
  • Standalone JRE installation is increasingly unnecessary, with centralized JDK management becoming the norm.

Java runtime environments continue to evolve. Choosing the right runtime based on your purpose and environment is key to stable Java application operation.

9. Frequently Asked Questions (FAQ)

This section summarizes common questions about Java Runtime Environment (JRE) and Java-related environment setup.

Q1: Do I need JRE or JDK?

A: If you only need to run Java applications, JRE is sufficient. However, if you want to develop, compile, or build Java programs, you need JDK (Java Development Kit). Since JDK includes JRE, installing JDK is generally the safest choice.

Q2: Should I choose the 32-bit or 64-bit version?

A: If your OS is 64-bit, the 64-bit JRE is recommended. Use the 32-bit version only for legacy applications or 32-bit operating systems when required.

Q3: How can I check the installed Java runtime version?

A: Run java -version in a command prompt or terminal to display the installed JRE/JDK version and architecture.

Q4: Is it dangerous to keep old JRE versions installed?

A: Yes. Older versions often contain known vulnerabilities and pose security risks. Uninstall unused or outdated versions as soon as possible.

Q5: How do I install JRE on Linux?

A: Most Linux distributions allow easy installation via package managers such as apt or yum.
Example for Ubuntu: sudo apt install openjdk-17-jre

Q6: What should enterprises consider when managing JRE/JDK versions?

A: Business systems often require specific certified versions. Avoid upgrading or downgrading without approval, and coordinate with IT departments or vendors. Timely security patch management is also critical.

10. Summary and Reference Links

In this article, we covered Java Runtime Environment (JRE) from its basic concepts to installation, troubleshooting, recent trends, and frequently asked questions.

Key Takeaways

  • JRE (Java Runtime Environment) is required to run Java applications
    It provides a stable execution foundation across Windows, macOS, and Linux.
  • Understanding the differences between JRE, JDK, and JVM is essential
    The appropriate choice depends on whether you are running or developing Java applications. Today, JRE is typically included with JDK.
  • Follow OS-specific procedures for installation, updates, and removal
    Regular updates and cleanup of unused versions improve security and stability.
  • Handle common issues calmly and methodically
    Most errors are caused by version mismatches or environment variable misconfiguration.
  • Stay informed about Java runtime trends
    OpenJDK distributions, modularization, and LTS versions are now standard considerations.

Reference Links and Recommended Resources

Java environments continue to evolve, but understanding the fundamentals allows you to use and operate Java applications with confidence. When questions arise, use this article and the reference links to maintain a stable and secure Java environment.