Collections

ArrayList list = new ArrayList();
        list.add("h");
        list.add("e");
        list.add("l");
        list.add("l");
        list.add("o");

        for (int i = 1; i < 10; i++) {
            list.add(i);
        }

        Iterator it = list.iterator();

        while (it.hasNext()) {
            out.println(it.next() + "<br/>");
        }

        HashSet hs = new HashSet();
        hs.add("A");
        hs.add("B");
        hs.add("C");
        hs.add("C");
        hs.add("C");

        HashMap hm = new HashMap();
        hm.put("a", "A");
        hm.put("b", "B");

        Iterator its = hs.iterator();

        while (its.hasNext()) {
            out.println(its.next() + "<br/>");
        }

        Iterator itr = hm.entrySet().iterator();

        while (itr.hasNext()) {
            Map.Entry pair = (Map.Entry) itr.next();
            out.println(pair.getKey() + " => " + pair.getValue() + "<br/>");
        }

        String[] strarr = new String[10];

        for (int i = 0; i < 10; i++) {
            strarr[i] = "abc" + i;
        }

        for (String valu : strarr) {
            out.println(valu);
        }

 
Ref:

1. http://stackoverflow.com/questions/85190/how-does-the-java-for-each-loop-work
2. http://stackoverflow.com/questions/4131655/what-is-the-difference-between-lists-arraylists-maps-hashmaps-collections-et
3. https://www.quora.com/What-is-the-difference-between-a-Set-and-a-Map-in-Java
4. http://stackoverflow.com/questions/1066589/iterate-through-a-hashmap
5. http://stackoverflow.com/questions/1200621/how-to-declare-an-array-in-java
6. http://stackoverflow.com/questions/1665834/how-can-i-initialize-a-string-array-with-length-0-in-java