Practice: JDK, JRE, and JVM

What do the abbreviations JDK, JRE and JVM stand for?

Which of the three components contains javac, and what does javac do?

Which component do you need in order to compile Java source code?

What does the JRE contain?

Build a Java setup checker: a program that prints the Java version, the Java vendor, the JVM name, the folder where the Java runtime is installed (java.home), the operating system with its architecture, and the bytecode version the runtime understands (java.class.version). Then explain which component each printed fact describes, and why two learners running the same program can see different output.

Run the program below in the code editor. Which message does it print, why, and what would it print on a runtime-only installation? (The program asks Java for its compiler with ToolProvider.getSystemJavaCompiler(), which gives back null, meaning no compiler, on an installation that has none.)

import javax.tools.JavaCompiler;
import javax.tools.ToolProvider;

public class CompilerCheck {
    public static void main(String[] args) {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        if (compiler != null) {
            System.out.println("A Java compiler is available: this runtime is part of a JDK.");
        } else {
            System.out.println("No Java compiler here: this is a runtime-only (JRE) installation.");
        }
        System.out.println("Runtime folder: " + System.getProperty("java.home"));
    }
}