What other Java tricks are there?

Java is a great language 🙂

Try-with-resources is not a trick, but rather a syntax simplification that keeps the code narrow.

Example

Autsch:
public ResultSet getPerson(int id) throws SQLException {
	try (PreparedStatement stmt = getConnection().prepareStatement("SELECT bla bla FROM persons WHERE id = " + id)) {
		return stmt.executeQuery();
	}
}


Besser:
public PersonData getPerson(int id) throws SQLException {
	try (PreparedStatement stmt = getConnection.prepareStatement("SELECT bla bla FROM persons WHERE id = ?")) {
		stmt.putInteger(1, id);
		try (ResultSet set = stmt.executeQuery()) {	
			if (set.next()) {
				return new PersonData(set.getString("name"), set.getInt("age"));
			}
			return null;
		}
	}
}


Das zweite mit normalem try, funktional identisch:
public PersonData getPerson(int id) throws SQLException {
	PreparedStatement stmt;
	try {
		stmt = getConnection.prepareStatement("SELECT bla bla FROM persons WHERE id = ?"
		stmt.putInteger(1, id);
		ResultSet set;
		try {	
			set = stmt.executeQuery();
			if (set.next()) {
				return new PersonData(set.getString("name"), set.getInt("age"));
			}
			return null;
		} finally {
			set.close();
		}
	} finally {
		stmt.close();
	}
}

(Was im Beispiel fehlt: getConnection() ist eine Methode, die prüft, ob die bestehende Verbindung noch gut ist und ggf. erneut öffnet, bevor sie zurückgegeben wird. Ein Pool mit einer Verbindung sozusagen. Diese ist bei Programmende natürlich zu closen. Ich bevorzuge Pooling gegenüber immer öffnen/schließen neuer Verbindungen für jeder Abfrage. Gibt Libraries, die genau diese Funktionalität bereithalten).

I always meet this Autsch method from colleagues, where the ResultSet is chopped somewhere outside. What is often forgotten (from ignorance): Also the ResultSet is to close. If you don’t do it, most drivers do it when closing the connection from which it comes. A closed ResultSet is returned.

Who programmed and used SQL objects beyond the query has nix of this simplification.

Memory leak. When testing with a manually managed connection, it works a few times but as soon as load gets on or you use a PoolLibrary, the most adventurous bugs are created with time. The try-with-resources are vllt here. “contra-productive” because the ResultSet is still needed.

In the second example with try-with-resources it can be seen immediately what is considered in the service life.

The third variant is functionally identical to the second, but in relation to a pretty chunk.

Oh, yes, your question:

Java features that I often and like to use:

• Collection.stream() – saves these clobular loops that fish anything out of an array, process and return to a new array
• () -> {} – abbreviation for Runnable and Callable
• Interfaces – Helpful in structuring and forming APIs where only certain methods should be externally visible
• Generics prevents a lot of casting (such as ArrayList does)
• ExecutorService – It’s hard to get to workerthreads.
• InputStream, OutputStream and ByteBuffer