Fixed #9. Added support for isString function

src/main/java/strman/Strman.java

@@ -118,12 +118,6 @@ public abstract class Strman {
     }
 
 
-    public static void validate(String value, Predicate<String> predicate, final Supplier<String> supplier) {
-        if (predicate.test(value)) {
-            throw new IllegalArgumentException(supplier.get());
-        }
-    }
-
     /**
      * Verifies that the needle is contained in the value. The search is case insensitive
      *
@@ -547,7 +541,21 @@ public abstract class Strman {
         return append(Stream.generate(() -> pad).limit(length - value.length()).collect(joining()), value);
     }
 
-    public static String decode(final String value, int digits, int radix) {
+    /**
+     * Checks whether Object is String
+     *
+     * @param value The input String
+     * @return true if Object is a String false otherwise
+     */
+    public static boolean isString(Object value) {
+        if (Objects.isNull(value)) {
+            throw new IllegalArgumentException("value can't be null");
+        }
+        return value instanceof String;
+    }
+
+
+    public static String decode(final String value, final int digits, final int radix) {
         validate(value, NULL_STRING_PREDICATE, NULL_STRING_MSG_SUPPLIER);
         return Arrays
                 .stream(value.split("(?<=\\G.{" + digits + "})"))
@@ -555,11 +563,17 @@ public abstract class Strman {
                 .collect(joining());
     }
 
-    public static String encode(String value, int digits, int radix) {
+    public static String encode(final String value, final int digits, final int radix) {
         validate(value, NULL_STRING_PREDICATE, NULL_STRING_MSG_SUPPLIER);
         return value.chars().mapToObj(ch -> leftPad(Integer.toString(ch, radix), "0", digits)).collect(joining());
     }
 
+    private static void validate(String value, Predicate<String> predicate, final Supplier<String> supplier) {
+        if (predicate.test(value)) {
+            throw new IllegalArgumentException(supplier.get());
+        }
+    }
+
     private static long countSubstr(String value, String subStr, boolean allowOverlapping, long count) {
         int position = value.indexOf(subStr);
         if (position == -1) {

src/test/java/strman/StrmanTest.java

@@ -438,6 +438,19 @@ public class StrmanTest {
         assertThat(leftPad("001", "0", 5), equalTo("00001"));
         assertThat(leftPad("0001", "0", 5), equalTo("00001"));
         assertThat(leftPad("00001", "0", 5), equalTo("00001"));
+    }
 
+    @Test
+    public void isString_shouldBeFalseWhenValueIsNotString() throws Exception {
+        assertFalse(isString(1));
+        assertFalse(isString(false));
+        assertFalse(isString(1.2));
+        assertFalse(isString(new String[]{}));
+    }
+
+    @Test
+    public void isString_shouldBeTrueWhenValueIsString() throws Exception {
+        assertTrue(isString("string"));
+        assertTrue(isString(""));
     }
 }