ClassLoader::isParallelCapable is added in JDK 9 (JDK-8165793). Existing class loader subclass that already has the same method may be broken.

java.lang.VerifyError: class org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader overrides final method java.lang.ClassLoader.isParallelCapable()Z
at java.lang.ClassLoader.defineClass1(java.base@9-ea/Native Method)
at java.lang.ClassLoader.defineClass(java.base@9-ea/ClassLoader.java:941)
at org.netbeans.JarClassLoader.doLoadClass(JarClassLoader.java:311)
at org.netbeans.ProxyClassLoader.selfLoadClass(ProxyClassLoader.java:259)
at org.netbeans.ProxyClassLoader.loadClass(ProxyClassLoader.java:187)
at java.lang.ClassLoader.loadClass(java.base@9-ea/ClassLoader.java:419)
at org.eclipse.osgi.baseadaptor.BaseAdaptor.createSystemBundleData(BaseAdaptor.java:355)
at org.eclipse.osgi.framework.internal.core.InternalSystemBundle.<init>(InternalSystemBundle.java:106)
at org.eclipse.osgi.framework.internal.core.Framework.createSystemBundle(Framework.java:283)
at org.eclipse.osgi.framework.internal.core.Framework.<init>(Framework.java:226)
at org.eclipse.osgi.framework.internal.core.EquinoxLauncher.internalInit(EquinoxLauncher.java:67)
at org.eclipse.osgi.framework.internal.core.EquinoxLauncher.init(EquinoxLauncher.java:37)
at org.eclipse.osgi.launch.Equinox.init(Equinox.java:178)
at org.netbeans.modules.netbinox.Netbinox.init(Netbinox.java:84)
at org.netbeans.core.netigso.Netigso.prepare(Netigso.java:167)
at org.netbeans.NetigsoHandle.turnOn(NetigsoHandle.java:138)
at org.netbeans.ModuleManager.enable(ModuleManager.java:1356)
at org.netbeans.ModuleManager.enable(ModuleManager.java:1173)
at org.netbeans.core.startup.ModuleList.installNew(ModuleList.java:340)
at org.netbeans.core.startup.ModuleList.trigger(ModuleList.java:276)
at org.netbeans.core.startup.ModuleSystem.restore(ModuleSystem.java:301)
at org.netbeans.core.startup.Main.getModuleSystem(Main.java:181)
at org.netbeans.core.startup.Main.getModuleSystem(Main.java:150)
at org.netbeans.core.startup.Main.start(Main.java:307)
at org.netbeans.core.startup.TopThreadGroup.run(TopThreadGroup.java:123)
at java.lang.Thread.run(java.base@9-ea/Thread.java:844)