Use Initialize-on-demand holder idiom for StateObjectFactory

As a result of 14f66ae, it might happen
that the MinimalState is shut down, even though it was never started. In
such a case, the class is implicitly loaded while stopping the plug-in.

When loading this class, the "stateObjectFactory" is initialized using
the PlatformAdmin provided by the PDE Build bundle. If this bundle is
stopped before the PDE Core bundle, an exception is thrown because the
PlatformAdmin is no longer available.

To resolve this, the StateObjectFactory is loaded only when required for
the first time.

Closes #1714

Author: ptziegler

ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/MinimalState.java

@@ -66,6 +66,10 @@
 
 public class MinimalState {
 
+	protected static class SingletonHolder {
+		protected static final StateObjectFactory STATE_OBJECT_FACTORY = BundleHelper.getPlatformAdmin().getFactory();
+	}
+
 	private static final IPreferenceChangeListener PREF_CHANGE_LISTENER = e -> {
 		if (e.getKey().equals("org.eclipse.jdt.launching.PREF_DEFAULT_ENVIRONMENTS_XML")) { //$NON-NLS-1$
 			Object oldValue = e.getOldValue() == null ? "" : e.getOldValue(); //$NON-NLS-1$
@@ -111,16 +115,10 @@ public void defaultVMInstallChanged(IVMInstall previous, IVMInstall current) {
 
 	private boolean fNoProfile;
 
-	protected static StateObjectFactory stateObjectFactory;
-
 	protected String fSystemBundle = IPDEBuildConstants.BUNDLE_OSGI;
 
-	static {
-		stateObjectFactory = BundleHelper.getPlatformAdmin().getFactory();
-	}
-
 	protected MinimalState(MinimalState state) {
-		this.fState = stateObjectFactory.createState(state.fState);
+		this.fState = SingletonHolder.STATE_OBJECT_FACTORY.createState(state.fState);
 		this.fState.setPlatformProperties(state.fState.getPlatformProperties());
 		this.fState.setResolver(BundleHelper.getPlatformAdmin().createResolver());
 		this.fId = state.fId;
@@ -213,8 +211,8 @@ public BundleDescription addBundle(Map<String, String> manifest, File bundleLoca
 		try {
 			// OSGi requires a dictionary over any map
 			Dictionary<String, String> dictionaryManifest = FrameworkUtil.asDictionary(manifest);
-			BundleDescription descriptor = stateObjectFactory.createBundleDescription(fState, dictionaryManifest,
-					bundleLocation.getAbsolutePath(), bundleId == -1 ? getNextId() : bundleId);
+			BundleDescription descriptor = SingletonHolder.STATE_OBJECT_FACTORY.createBundleDescription(fState,
+					dictionaryManifest, bundleLocation.getAbsolutePath(), bundleId == -1 ? getNextId() : bundleId);
 			// new bundle
 			if (bundleId == -1 || !fState.updateBundle(descriptor)) {
 				fState.addBundle(descriptor);

ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/PDEState.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2005, 2016 IBM Corporation and others.
+ * Copyright (c) 2005, 2025 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -77,7 +77,7 @@ public PDEState(URI[] target, boolean addResolver, boolean removeDuplicates, IPr
 	}
 
 	private void createNewTargetState(boolean resolve, URI[] uris, IProgressMonitor monitor) {
-		fState = stateObjectFactory.createState(resolve);
+		fState = SingletonHolder.STATE_OBJECT_FACTORY.createState(resolve);
 		if (resolve) {
 			final String systemBSN = getSystemBundle();
 			Comparator<BaseDescription> policy = systemBundlesFirst(systemBSN)