Fix Javadoc warnings (Java 21)

Author: garydgregory

src/main/java/org/apache/commons/pool2/BaseKeyedPooledObjectFactory.java

@@ -34,6 +34,13 @@
  */
 public abstract class BaseKeyedPooledObjectFactory<K, V> extends BaseObject implements KeyedPooledObjectFactory<K, V> {
 
+    /**
+     * Constructs a new instance.
+     */
+    public BaseKeyedPooledObjectFactory() {
+        // empty
+    }
+
     /**
      * Reinitializes an instance to be returned by the pool.
      * <p>

src/main/java/org/apache/commons/pool2/BaseObject.java

@@ -23,6 +23,13 @@
  */
 public abstract class BaseObject {
 
+    /**
+     * Constructs a new instance.
+     */
+    public BaseObject() {
+        // empty
+    }
+
     @Override
     public String toString() {
         final StringBuilder builder = new StringBuilder();

src/main/java/org/apache/commons/pool2/BaseObjectPool.java

@@ -31,6 +31,13 @@ public abstract class BaseObjectPool<T> extends BaseObject implements ObjectPool
 
     private volatile boolean closed;
 
+    /**
+     * Constructs a new instance.
+     */
+    public BaseObjectPool() {
+        // empty
+    }
+
     /**
      * Not supported in this base implementation. Subclasses should override
      * this behavior.

src/main/java/org/apache/commons/pool2/BasePooledObjectFactory.java

@@ -32,6 +32,13 @@
  */
 public abstract class BasePooledObjectFactory<T> extends BaseObject implements PooledObjectFactory<T> {
 
+    /**
+     * Constructs a new instance.
+     */
+    public BasePooledObjectFactory() {
+        // empty
+    }
+
     /**
      *  No-op.
      *

src/main/java/org/apache/commons/pool2/impl/BaseObjectPoolConfig.java

@@ -291,6 +291,13 @@ public abstract class BaseObjectPoolConfig<T> extends BaseObject implements Clon
 
     private String jmxNameBase = DEFAULT_JMX_NAME_BASE;
 
+    /**
+     * Constructs a new instance.
+     */
+    public BaseObjectPoolConfig() {
+        // empty
+    }
+
     /**
      * Gets the value for the {@code blockWhenExhausted} configuration attribute for pools created with this configuration instance.
      *

src/main/java/org/apache/commons/pool2/impl/DefaultEvictionPolicy.java

@@ -42,6 +42,13 @@
  */
 public class DefaultEvictionPolicy<T> implements EvictionPolicy<T> {
 
+    /**
+     * Constructs a new instance.
+     */
+    public DefaultEvictionPolicy() {
+        // empty
+    }
+
     @Override
     public boolean evict(final EvictionConfig config, final PooledObject<T> underTest, final int idleCount) {
         // @formatter:off

src/main/java/org/apache/commons/pool2/impl/GenericObjectPool.java

@@ -363,10 +363,6 @@ public T borrowObject(final Duration borrowMaxWaitDuration) throws Exception {
         return p.getObject();
     }
 
-    private Duration durationSince(final Instant startInstant) {
-        return Duration.between(startInstant, Instant.now());
-    }
-
     /**
      * Borrows an object from the pool using the specific waiting time which only
      * applies if {@link #getBlockWhenExhausted()} is true.
@@ -604,6 +600,10 @@ private void destroy(final PooledObject<T> toDestroy, final DestroyMode destroyM
         }
     }
 
+    private Duration durationSince(final Instant startInstant) {
+        return Duration.between(startInstant, Instant.now());
+    }
+
     /**
      * Tries to ensure that {@code idleCount} idle instances exist in the pool.
      * <p>

src/main/java/org/apache/commons/pool2/impl/GenericObjectPoolConfig.java

@@ -57,6 +57,13 @@ public class GenericObjectPoolConfig<T> extends BaseObjectPoolConfig<T> {
 
     private int minIdle = DEFAULT_MIN_IDLE;
 
+    /**
+     * Constructs a new instance.
+     */
+    public GenericObjectPoolConfig() {
+        // empty
+    }
+
     @SuppressWarnings("unchecked")
     @Override
     public GenericObjectPoolConfig<T> clone() {