### Question:
StringUtils { public static boolean isNumeric(String str) { if (str == null) { return false; } int sz = str.length(); for (int i = 0; i < sz; i++) { if (!Character.isDigit(str.charAt(i))) { return false; } } return true; } private  StringUtils(); static int length(final CharSequence cs); static String repeat(final String str, final int repeat); static String repeat(final String str, final String separator, final int repeat); static String removeEnd(final String str, final String remove); static String repeat(final char ch, final int repeat); static String stripEnd(final String str, final String stripChars); static String replace(final String text, final String searchString, final String replacement); static String replace(final String text, final String searchString, final String replacement, int max); static boolean isBlank(String str); static boolean isEmpty(String str); static boolean isNoneEmpty(final String... ss); static boolean isAnyEmpty(final String... ss); static boolean isNotEmpty(String str); static boolean isEquals(String s1, String s2); static boolean isInteger(String str); static int parseInteger(String str); static boolean isJavaIdentifier(String s); static boolean isContains(String values, String value); static boolean isContains(String[] values, String value); static boolean isNumeric(String str); static String toString(Throwable e); static String toString(String msg, Throwable e); static String translate(String src, String from, String to); static String[] split(String str, char ch); static String join(String[] array); static String join(String[] array, char split); static String join(String[] array, String split); static String join(Collection<String> coll, String split); static String getQueryStringValue(String qs, String key); static Map<String, String> parseQueryString(String qs); static String getServiceKey(Map<String, String> ps); static String toQueryString(Map<String, String> ps); static String camelToSplitName(String camelName, String split); static String toArgumentString(Object[] args); static final String EMPTY; static final int INDEX_NOT_FOUND; static final String[] EMPTY_STRING_ARRAY; }### Answer:
@Test public void testIsNumeric() throws Exception { assertThat(StringUtils.isNumeric("123"), is(true)); assertThat(StringUtils.isNumeric("1a3"), is(false)); assertThat(StringUtils.isNumeric(null), is(false)); }