}

  @GwtIncompatible // Predicates.instanceOf
  public void testIsInstanceOf_subclass() {
    Predicate<@Nullable Object> isNumber = Predicates.instanceOf(Number.class);

    assertTrue(isNumber.apply(1));
    assertTrue(isNumber.apply(2.0f));
    assertFalse(isNumber.apply(""));
    assertFalse(isNumber.apply(null));
  }

  @GwtIncompatible // Predicates.instanceOf
  public void testIsInstanceOf_interface() {

        assertFalse(StringUtil.isNumber(null));
        assertTrue(StringUtil.isNumber("0123456789"));
        assertFalse(StringUtil.isNumber("aaaBBBccc"));
        assertFalse(StringUtil.isNumber("０１２３４５６７８９"));
        assertFalse(StringUtil.isNumber(""));
        assertFalse(StringUtil.isNumber("01234abcdef"));
        assertFalse(StringUtil.isNumber("abcdef01234"));
    }

    /**
     *
     */

  }

  @GwtIncompatible // Predicates.instanceOf
  public void testIsInstanceOf_subclass() {
    Predicate<@Nullable Object> isNumber = Predicates.instanceOf(Number.class);

    assertTrue(isNumber.apply(1));
    assertTrue(isNumber.apply(2.0f));
    assertFalse(isNumber.apply(""));
    assertFalse(isNumber.apply(null));
  }

  @GwtIncompatible // Predicates.instanceOf
  public void testIsInstanceOf_interface() {

    }

    /**
     * 文字列が数値のみで構成されているかどうかを返します。
     *
     * @param s
     *            文字列
     * @return 数値のみで構成されている場合、<code>true</code>
     */
    public static boolean isNumber(final String s) {
        if (isEmpty(s)) {
            return false;
        }

        final int size = s.length();
        for (int i = 0; i < size; i++) {
            final char chr = s.charAt(i);