Remove static singleton field from base classes and ensure singletons…

… follow the same pattern.

This avoid cycles in clinits that hard to optimize.

RELNOTES=n/a
PiperOrigin-RevId: 590989450

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/ImmutableCollection.java

@@ -22,7 +22,6 @@
 import java.io.Serializable;
 import java.util.AbstractCollection;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Iterator;
 import java.util.Spliterator;
 import java.util.function.Predicate;
@@ -38,9 +37,6 @@ public abstract class ImmutableCollection<E> extends AbstractCollection<E> imple
   static final int SPLITERATOR_CHARACTERISTICS =
       Spliterator.IMMUTABLE | Spliterator.NONNULL | Spliterator.ORDERED;
 
-  static final ImmutableCollection<Object> EMPTY_IMMUTABLE_COLLECTION =
-      new ForwardingImmutableCollection<Object>(Collections.emptyList());
-
   ImmutableCollection() {}
 
   public abstract UnmodifiableIterator<E> iterator();

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/ImmutableList.java

@@ -40,8 +40,6 @@
 @SuppressWarnings("serial") // we're overriding default serialization
 public abstract class ImmutableList<E> extends ImmutableCollection<E>
     implements List<E>, RandomAccess {
-  static final ImmutableList<Object> EMPTY =
-      new RegularImmutableList<Object>(Collections.emptyList());
 
   ImmutableList() {}
 
@@ -52,7 +50,7 @@ public abstract class ImmutableList<E> extends ImmutableCollection<E>
   // Casting to any type is safe because the list will never hold any elements.
   @SuppressWarnings("unchecked")
   public static <E> ImmutableList<E> of() {
-    return (ImmutableList<E>) EMPTY;
+    return (ImmutableList<E>) RegularImmutableList.EMPTY;
   }
 
   public static <E> ImmutableList<E> of(E element) {

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/ImmutableMap.java

@@ -50,7 +50,6 @@
  * @author Hayward Chan
  */
 public abstract class ImmutableMap<K, V> implements Map<K, V>, Serializable {
-  static final ImmutableMap<Object, Object> EMPTY = new RegularImmutableMap<Object, Object>();
 
   abstract static class IteratorBasedImmutableMap<K, V> extends ImmutableMap<K, V> {
     abstract UnmodifiableIterator<Entry<K, V>> entryIterator();
@@ -92,7 +91,7 @@ public UnmodifiableIterator<Entry<K, V>> iterator() {
   }
 
   public static <K, V> ImmutableMap<K, V> of() {
-    return (ImmutableMap<K, V>) EMPTY;
+    return (ImmutableMap<K, V>) RegularImmutableMap.EMPTY;
   }
 
   public static <K, V> ImmutableMap<K, V> of(K k1, V v1) {

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/RegularImmutableList.java

@@ -16,6 +16,7 @@
 
 package com.google.common.collect;
 
+import static java.util.Collections.emptyList;
 import static java.util.Collections.unmodifiableList;
 
 import java.util.List;
@@ -26,6 +27,9 @@
  * @author Hayward Chan
  */
 class RegularImmutableList<E> extends ForwardingImmutableList<E> {
+
+  static final ImmutableList<Object> EMPTY = new RegularImmutableList<Object>(emptyList());
+
   private final List<E> delegate;
   E forSerialization;
 

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/RegularImmutableMap.java

@@ -25,6 +25,8 @@
  */
 final class RegularImmutableMap<K, V> extends ForwardingImmutableMap<K, V> {
 
+  static final ImmutableMap<Object, Object> EMPTY = new RegularImmutableMap<Object, Object>();
+
   RegularImmutableMap(Map<? extends K, ? extends V> delegate) {
     super(delegate);
   }