Discussion: Compiling and running with newer versions of Java

[ggliv]

Dr. Cotterell started a discussion on running the project with later versions of Java here.

I tried to reproduce the compilation issues mentioned in that comment using Java 17 on my machine and was unable to get the same errors. Here's my Java version:

$ java -version
openjdk version "17.0.15" 2025-04-15
OpenJDK Runtime Environment (build 17.0.15+6)
OpenJDK 64-Bit Server VM (build 17.0.15+6, mixed mode, sharing)

Here's what I get trying to compile with the provided command:

$ /usr/lib/jvm/java-17-openjdk/bin/javac --release 8 -d .backend_classes -cp backend/cp:backend/cp/javax.json-1.0.jar backend/**/*.java
backend/cp/traceprinter/InMemory.java:39: error: cannot find symbol
    VirtualMachine vm;
    ^
  symbol:   class VirtualMachine
  location: class InMemory
backend/cp/traceprinter/InMemory.java:183: error: cannot find symbol
    VirtualMachine launchVM(String className) {
    ^
  symbol:   class VirtualMachine
  location: class InMemory
backend/cp/traceprinter/InMemory.java:267: error: cannot find symbol
    LaunchingConnector theCommandLineLaunchConnector() {
    ^
  symbol:   class LaunchingConnector
  location: class InMemory
backend/cp/traceprinter/InMemory.java:19: error: package com.sun.jdi does not exist
import com.sun.jdi.*;
^
backend/cp/traceprinter/InMemory.java:20: error: package com.sun.jdi.connect does not exist
import com.sun.jdi.connect.*;
^
backend/cp/traceprinter/JDI2JSON.java:56: error: cannot find symbol
    private VirtualMachine vm;
            ^
  symbol:   class VirtualMachine
  location: class JDI2JSON
[...]

These all seemed to come from the tools.jar library not being available. When I passed that in from a Java 8 install I also have, compilation worked fine.

$ /usr/lib/jvm/java-17-openjdk/bin/javac --release 8 -d .backend_classes -cp backend/cp:backend/cp/javax.json-1.0.jar:/usr/lib/jvm/java-8-openjdk/lib/tools.jar backend/**/*.java
Note: backend/cp/traceprinter/ramtools/RAMRun.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

I could then run this with Java 17 using /usr/lib/jvm/java-17-openjdk/bin/java -cp .backend_classes:backend/cp:backend/cp/javax.json-1.0.jar:/usr/lib/jvm/java-8-openjdk/lib/tools.jar traceprinter.InMemory. This worked fine.

It appears that the tools.jar library was removed in Java 9 and most of its functionality was incorporated into the java.compiler built-in package. That package isn't a drop-in replacement though. If we wanted to prioritize making Java 17 our target platform, we might be able to rewrite portions of traceprinter to use this new package.