src/java.base/share/classes/java/util/Scanner.java

rev 53930 : 8148917: enhanced-for statement should allow streams
Reviewed-by: XXX

@@ -305,11 +305,11 @@
  * </dl>
  * <p>Whitespace is not significant in the above regular expressions.
  *
  * @since   1.5
  */
-public final class Scanner implements Iterator<String>, Closeable {
+public final class Scanner implements Iterator<String>, Closeable, IterableOnce<String> {
 
     // Internal buffer used to hold input
     private CharBuffer buf;
 
     // Size of internal character buffer

@@ -370,10 +370,13 @@
     private PatternLRUCache patternCache = new PatternLRUCache(7);
 
     // A holder of the last IOException encountered
     private IOException lastException;
 
+    // Whether this Scanner, as IterableOnce, has been consumed
+    private boolean consumed = false;
+
     // Number of times this scanner's state has been modified.
     // Generally incremented on most public APIs and checked
     // within spliterator implementations.
     int modCount;
 

@@ -1478,10 +1481,28 @@
                 throwFor();
         }
     }
 
     /**
+     * Returns this Scanner instance. This method exists to implement the
+     * {@link IterableOnce} interface, allowing a Scanner instance to be
+     * used in an enhanced-for ("for each") statement. This method can be
+     * called no more than once on any Scanner instance. The second and
+     * subsequent calls result in an exception.
+     *
+     * @throws IllegalStateException if this method had been called previously
+     * @return this Scanner instance
+     */
+    public Scanner iterator() {
+        if (consumed) {
+            throw new IllegalStateException();
+        }
+        consumed = true;
+        return this;
+    }
+
+    /**
      * The remove operation is not supported by this implementation of
      * {@code Iterator}.
      *
      * @throws UnsupportedOperationException if this method is invoked.
      * @see java.util.Iterator