How can I parse/format dates with LocalDateTime? (Java 8)

Parsing date and time To create a LocalDateTime object from a string you can use the static LocalDateTime.parse() method. It takes a string and a DateTimeFormatter as parameter. The DateTimeFormatter is used to specify the date/time pattern. String str = “1986-04-08 12:30”; DateTimeFormatter formatter = DateTimeFormatter.ofPattern(“yyyy-MM-dd HH:mm”); LocalDateTime dateTime = LocalDateTime.parse(str, formatter); Formatting date and … Read more

How to validate a JTextField?

Any validation in Swing can be performed using an InputVerifier. 1. First create your own input verifier: public class MyInputVerifier extends InputVerifier { @Override public boolean verify(JComponent input) { String text = ((JTextField) input).getText(); try { BigDecimal value = new BigDecimal(text); return (value.scale() <= Math.abs(4)); } catch (NumberFormatException e) { return false; } } } … Read more

Sending and receiving UDP packets?

The receiver must set port of receiver to match port set in sender DatagramPacket. For debugging, try listening on port > 1024 (e.g. 5000 or 9000). Ports < 1024 are normally used by system services and need admin access to bind on such a port. If the receiver sends packet to the hard-coded port it’s … Read more

java.lang.ClassNotFoundException: org.postgresql.Driver, Android

You need to add the PostgreSQL JDBC Driver in your project as mentioned in Gradle: implementation ‘org.postgresql:postgresql:42.2.10’ Maven: <dependency> <groupId>org.postgresql</groupId> <artifactId>postgresql</artifactId> <version>42.2.10</version> </dependency> You can also download the JAR and import to your project manually. NOTE: Compile as used in this answer is deprecated. Replace with implementation as per 3.

PrintWriter and PrintStream never throw IOExceptions

I think that since System.out and System.err are instances of PrintStream, some more relaxed error handling was provided. This was probably, as other posters have mentioned, to smooth the way for those transitioning from C/C++ circa 1995. When the Reader/Writer API was added, PrintWriter was created to parallel the existing PrintStream. One application where this … Read more