6361826: (reflect) provide method for mapping strings to class object for primitive types

Reviewed-by: rriggs, mchung

src/java.base/share/classes/java/lang/Class.java

@@ -438,6 +438,9 @@ public final class Class<T> implements java.io.Serializable,
      * If {@code name} denotes a primitive type or void, for example {@code I},
      * an attempt will be made to locate a user-defined class in the unnamed package
      * whose name is {@code I} instead.
+     * To obtain a {@code Class} object for a named primitive type
+     * such as {@code int} or {@code long} use {@link
+     * #forPrimitiveName(String)}.
      *
      * <p> To obtain the {@code Class} object associated with an array class,
      * the name consists of one or more {@code '['} representing the depth
@@ -628,6 +631,41 @@ public final class Class<T> implements java.io.Serializable,
         }
     }
 
+    /**
+     * {@return the {@code Class} object associated with the
+     * {@linkplain #isPrimitive() primitive type} of the given name}
+     * If the argument is not the name of a primitive type, {@code
+     * null} is returned.
+     *
+     * @param primitiveName the name of the primitive type to find
+     *
+     * @throws NullPointerException if the argument is {@code null}
+     *
+     * @jls 4.2 Primitive Types and Values
+     * @jls 15.8.2 Class Literals
+     * @since 22
+     */
+    public static Class<?> forPrimitiveName(String primitiveName) {
+        return switch(primitiveName) {
+        // Integral types
+        case "int"     -> int.class;
+        case "long"    -> long.class;
+        case "short"   -> short.class;
+        case "char"    -> char.class;
+        case "byte"    -> byte.class;
+
+        // Floating-point types
+        case "float"   -> float.class;
+        case "double"  -> double.class;
+
+        // Other types
+        case "boolean" -> boolean.class;
+        case "void"    -> void.class;
+
+        default        -> null;
+        };
+    }
+
     /**
      * Creates a new instance of the class represented by this {@code Class}
      * object.  The class is instantiated as if by a {@code new}