Added setter for Builder.option (apache#33)

* added separate setter for Builder.opt

* added setter for option name with validation

* fixed checkstyle error

Author: waso

src/main/java/org/apache/commons/cli/Option.java

@@ -51,7 +51,7 @@ public class Option implements Cloneable, Serializable {
     public static final class Builder {
 
         /** The name of the option */
-        private final String option;
+        private String option;
 
         /** description of the option */
         private String description;
@@ -87,6 +87,18 @@ private Builder(final String option) throws IllegalArgumentException {
             this.option = OptionValidator.validate(option);
         }
 
+        /**
+         * Sets the name of the Option.
+         *
+         * @param opt the name of the Option
+         * @return this builder, to allow method chaining
+         * @throws IllegalArgumentException if there are any non valid Option characters in {@code opt}
+         */
+        public Builder opt(String opt) throws IllegalArgumentException {
+            this.option = OptionValidator.validate(opt);
+            return this;
+        }
+
         /**
          * Sets the display name for the argument value.
          *

src/test/java/org/apache/commons/cli/OptionTest.java

@@ -109,6 +109,8 @@ public void testBuilderMethods() {
             String.class);
         checkOption(Option.builder("a").desc("desc").type(Integer.class).build(), "a", "desc", null, Option.UNINITIALIZED, null, false, false, defaultSeparator,
             Integer.class);
+        checkOption(Option.builder().opt("a").desc("desc").type(Integer.class).build(), "a", "desc", null, Option.UNINITIALIZED, null, false, false,
+                defaultSeparator, Integer.class);
     }
 
     @Test