web development helpdesk

Sometimes an api will return you an Enumeration but what you want is a List. The Collections class has a utility method that creates a List containing the elements from the Enumeration.

Enumeration en = someMethodThatReturnsEnumeration();
List list = Collections.list(en);

written by objects \\ tags: collections, Enumeration, list

Java provides a convenient Collections.sort() method to sort a List of Object’s. The Objects in the list are required to implement the Comparable interface and the compareTo() method is used to compare Objects.

When an alternate sort order is needed you can do that using a Comparator which is passed to the sort() call.

The following example shows how you could sort a list of strings where the string contained a number (that should be sorted numerically) and a string (to be sorted alphabetically).

List<String> list = Arrays.asList(
   new String[] { "34 abc", "123 dfd", "34 xyz", "12 xxx" });

Collections.sort(list, new Comparator<String>() {

	@Override
	public int compare(String s1, String s2) {
		
		// separate the number and string
		
		String[] tokens1 = s1.split(" ");
		String[] tokens2 = s2.split(" ");
		
		// compare the number from each item
		
		int compare = Integer.parseInt(tokens1[0]) - Integer.parseInt(tokens2[0]);
		
		// If number same compare the string
		
		return compare==0 ? tokens1[1].compareTo(tokens2[1]) : compare;
	}
});

written by objects \\ tags: comparable, comparator, list, sort

The DBUtil library from Apache provides a set of class for doing a variety of standard database tasks.

eg. To make a query becomes as simple as the following, providing the result set as a List of arrays where each list elements contains a row.

QueryRunner runner = new QueryRunner();
ArrayListHandler handler = new ArrayListHandler();
List<Object[]> result = runner.query(connection,
    "SELECT * FROM MyTable WHERE name=?", handler, "Joe Smith");
DbUtils.close(conn); 

written by objects \\ tags: apache, jdbc DBUtil, list, query, ResultSet