The JRE software package includes the Java Virtual Machine (JVM), the Java Class Library, the Java command, and other infrastructure.

The Java Runtime Environment or JRE contains everything required to run Java applications on your system.

Examples of applications that use Java are numerous and widespread but include web browsers, office applications and even mainstream games like Minecraft are based on Java. Java is a programming language and software platform. Why would you need the JDK then? Because the application server will convert JSP into Java servlets and needs to use the JDK to compile the servlets. For example, if you are deploying a web application with JSP, you are technically just running Java programs inside the application server. Sometimes, even if you are not planning to do any Java development on a computer, you still need the JDK installed. The new license permits certain uses, such as personal use and development use, at no cost - but other uses authorized under prior Oracle JDK licenses may no longer be available. The new Oracle Technology Network License Agreement for Oracle Java SE is substantially different from prior Oracle JDK licenses. It is capable of creating and compiling programs. It has everything the JRE has, but also the compiler (javac) and tools (like javadoc and jdb).

The JDK is the Java Development Kit, the full-featured SDK for Java.

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