[tautschnig]

Building the models with JDK 25 (the default JDK on Ubuntu 26.04, and
thus on GitHub's ubuntu-latest runners) fails with three errors:

• Object.java: "flexible constructors is not supported in -source 8".
  java.lang.Object has no superclass, so javac 25 treats every
  statement in its constructor as part of a constructor prologue
  (JEP 513). Initialise cproverMonitorCount in its declaration instead.
• Class.java: ClassLoader.checkClassLoaderPermission no longer exists.
  As the call was already passing null for the caller class, it did
  not check anything; comment it out like the original call.
• URLEncoder.java: package sun.security.action does not exist. Read the
  file.encoding property with System.getProperty: doPrivileged has no
  effect without a security manager.

With these changes the models build with JDK 11, 17 and 25. With
JDK 17, the bytecode of Class differs only in the removed call and
constant-pool indices, and that of Object only in the constructor no
longer storing 0 to cproverMonitorCount, which is the default value of
the field.

CBMC's CodeQL workflow builds JBMC, including these models, on ubuntu-latest, which is moving to Ubuntu 26.04 and thus JDK 25; it currently fails because of the first two of these errors (the version of the models that CBMC uses predates URLEncoder.java).

[Copilot]

🟢 Approval recommended

No active review issues are recorded for the JDK 25 compatibility changes.

No open issues 🎉

What changed in this PR

Updates the Java models for JDK 25 compilation, addressing compatibility issues that affect JBMC builds in CBMC’s CodeQL workflow.

Changes:

• Moves cproverMonitorCount initialization from the Object constructor to its field declaration.
• Comments out the call to the removed ClassLoader.checkClassLoaderPermission method.
• Replaces the internal privileged property lookup with System.getProperty("file.encoding").

File	Description
src/​main/​java/​java/​net/​URLEncoder.java	Removes internal security imports and reads the encoding property directly.
src/​main/​java/​java/​lang/​Object.java	Moves field initialization to avoid JDK 25 constructor compilation restrictions.
src/​main/​java/​java/​lang/​Class.java	Disables a permission-check call unavailable in JDK 25.

_{Review effort: Balanced}