java工具类

public class TestMap {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Map<String, String> map = new HashMap<String, String>();
        map.put("1", "11");
        map.put("2", "22");
        map.put("2", "13");
        map.put("4", "44");
        // one
        Set<String> key = map.keySet();
        for (Iterator<String> it = key.iterator(); it.hasNext();) {
            String s = (String) it.next();
            System.out.println("key:" + s + " value:" + map.get(s));
        }
        //two
        for (Entry<String, String> entry : map.entrySet()) {
            System.out.println("Key = " + entry.getKey() + ", Value = "
                    + entry.getValue());
        }
        //three
        // 遍历map中的键
        for (String myKey : map.keySet()) {
            System.out.println("Key = " + myKey);
        }
        // 遍历map中的值
        for (String value : map.values()) {
            System.out.println("Value = " + value);
        }
    }
}

public static <T> boolean listNotNull(List<T> t) {
        return t != null && t.size() > 0;
    }