JRE

The JVM needs access to standard classes every program uses:
java.lang.Objectjava.lang.Systemjava.lang.String- etc.
Your program might use additional classes from the standard Java libraries.
java.util.Scanner
These standard library classes are defined in the Java Platform Standard Edition API Specification or Java SE.
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Java SE defines an extensive set of classes for everything from basic programming, to file I/O, graphical application development, database access, networking, and more.
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Anyone could write their own implementations of these classes; as long as they conform to the Java SE specification, any Java program would be able to use them.
We need a JVM and the Java SE Platform in order to run a program.
The combination of JVM, Java SE Platform, and various supporting files and utilities comprise the Java Runtime Environment (JRE).
- Anyone with a JRE installed can run a Java application.