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Java Virtual Machine (JVM) is a Java virtual machine. The main reason why Java can be cross-platform is because of the Java Virtual Machine, all programs must first be compiled into a. Class file that can run on the JVM. So Java programs don’t need to run directly on the operating system. It is the virtual machine that interprets the program to the local system.
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The Java Runtime Environment (JRE) is a Java runtime environment for Users of Java programs. However, the JRE program is required to run during development. The class library lib is called when the JVM executes the. Class file. The JRE directory can be found in the JDK installation directory. There are two folders, bin and lib, which can be regarded as the JVM. The bin folder stores the libraries required by the JVM, and the JVM and lib together make the JRE. So after the Java program is compiled into a. Class file, you can send the. Class file to someone along with the JRE file, which has the java.exe running the. Class file. So as long as the COMPUTER has JRE installed, you can run Java programs.
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The Java Development Kit (JDK) is the Java development kit for developers. The SDK provides the Java development environment and running environment. The important files in the JDK directory are bin, include, lib, and jre. So the relationship is that the JDK contains the JRE, and the JRE contains the JVM. Bin is the main compiler (javac.exe), include includes header files used to interact with the JVM, lib class libraries, and jre Java running environment.
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The SOFTWARE Development Kit (SDK) is a Java software development package, which contains function libraries and compiler programs. It is mainly used by Java application developers.