unitsofmeasurement#124: fix handling of powered units (creation and s…

…imple formatting)

src/main/java/tech/units/indriya/AbstractUnit.java

@@ -553,7 +553,7 @@ else if (n == 0)
 	 * @return the result of raising this unit to the exponent.
 	 */
 	@Override
-	public final Unit<?> pow(int n) {
+	public Unit<?> pow(int n) {
 		if (n > 0)
 			return this.multiply(this.pow(n - 1));
 		else if (n == 0)

src/main/java/tech/units/indriya/format/SimpleUnitFormat.java

@@ -719,6 +719,16 @@ public Appendable format(Unit<?> unit, Appendable appendable) throws IOException
 
       // Product unit.
       ProductUnit<?> productUnit = (ProductUnit<?>) unit;
+
+      // Special case: self-powered product unit
+      if (productUnit.getUnitCount() == 1 && productUnit.getUnit(0) instanceof ProductUnit) {
+          final ProductUnit<?> powerUnit = (ProductUnit<?>) productUnit.getUnit(0);
+          // is the sub-unit known under a given label?
+          if (nameFor(powerUnit) == null)
+              // apply the power to the sub-units and format those instead
+              return format(ProductUnit.ofPow(powerUnit, productUnit.getUnitPow(0)), appendable);
+      }
+
       int invNbr = 0;
 
       // Write positive exponents first.

src/main/java/tech/units/indriya/unit/ProductUnit.java

@@ -211,6 +211,11 @@ public static Unit<?> ofPow(Unit<?> unit, int n) {
     return getInstance(unitElems, new Element[0]);
   }
 
+  @Override
+  public Unit<?> pow(int n) {
+      return new ProductUnit<>(new Element[] { new Element(this, n, 1) });
+  }
+
   /**
    * Returns the number of unit elements in this product.
    *