add missing javadoc to class and main constructor

oshdb-util/src/main/java/org/heigit/bigspatialdata/oshdb/util/celliterator/LazyEvaluatedObject.java

@@ -2,18 +2,38 @@
 
 import java.util.function.Supplier;
 
+/**
+ * A lazily evaluated object.
+ * 
+ * <p>Useful as a wrapper to hold values which are potentially expensive to
+ * calculate, but might sometimes not be requested.</p>
+ *
+ * @param <T> the (arbitrary) type of data to hold
+ */
 public class LazyEvaluatedObject<T> implements Supplier<T> {
   private T value = null;
   private boolean evaluated = false;
   private Supplier<T> evaluator;
 
+  /**
+   * Constructs a {@link LazyEvaluatedObject} using a {@code evaluator} (supplier function) which
+   * returns a value of generic type {@code T}, when requested from this object.
+   *
+   * @param evaluator a {@link Supplier} function which returns the value of interest when executed
+   */
   public LazyEvaluatedObject(Supplier<T> evaluator) {
     this.evaluator = evaluator;
   }
 
   /**
-   * Generic constructor for a {@link LazyEvaluatedObject} using a {@code value} of generic type
-   * {@code T}.
+   * Constructs a {@link LazyEvaluatedObject} using an already known {@code value} of generic
+   * type {@code T}.
+   *
+   * <p>This simply wraps the value with a supplier method, but can be useful in situations where
+   * sometimes an expensive to calculate value is already know, but one wants to use the lazy
+   * evaluated interface for the remaining cases.</p>
+   *
+   * @param value the value to store
    */
   public LazyEvaluatedObject(T value) {
     this.value = value;