/My personal blog about software development 2026-01-17T12:04:52+01:00 Rafał Garbowski / Jekyll © 2026 Rafał Garbowski /assets/img/favicons/favicon.ico /assets/img/favicons/favicon-96x96.png 2025-11-29T00:00:00+01:00 2025-11-29T00:00:00+01:00 /posts/ocp-17-exam-chapter-15/ Rafał Garbowski

Java provides JDBC interfaces, while database libraries provides implementations - except implementation of DriverManager, which is used to create connection (Q.1) if autocommit is enabled (default), then commit happens after every statement (Q.6) if nothing to rollback (changes has been commited), then rollback doesn’t throw any Exception (Q.6) rollback will throw if you try to rollback ...

2025-10-25T00:00:00+02:00 2025-10-25T00:00:00+02:00 /posts/ocp-17-exam-chapter-14/ Rafał Garbowski

Streams byte streams are called *InputStream/*OutputStream, where character streams are *Reader/*Writer exceptions are PrintWriter and PrintStream exam my trick us by wrapping Writer/Reader into Input/OutputStream or wrapping InputStream into OutputStream be aware that not all readers support mark(int), so program might for some readers throw IOException ...

2025-09-06T00:00:00+02:00 2025-09-06T00:00:00+02:00 /posts/ocp-17-exam-chapter-13/ Rafał Garbowski

Executors be aware whether Executors.newSingleThreadExecutor is used, because running on single thread automatically synchronizes executions, so result will be always consistent (Q.22) awaitTermination(1, TimeUnit.SECONDS) returns false instead of throwing timeout when tasks execution didn’t finish (Q.12) be aware of methods of ScheduledExecutorService - only 1 accepts C...

2025-08-09T00:00:00+02:00 2025-08-09T00:00:00+02:00 /posts/ocp-17-exam-chapter-12/ Rafał Garbowski

Note: Java Platform Module System was introduced in JDK 9 in project Jigsaw. In Java 25 modules would be available through imports like regular classes. Running and packaging simple module Folder structure of app: - app - src/pkg - App.java // prints hello world - module-info.java // only module app { } Package names must be unique: e.g. I cannot add class in package “java.util...

2025-07-31T00:00:00+02:00 2025-07-31T00:00:00+02:00 /posts/EqualsIncompatibleType/ Rafał Garbowski

Let’s consider the following example: var list = List.of(1); var first1 = list.stream().findFirst(); var first2 = list.getFirst(); if (Objects.equals(first1, first2)) { // compiles, just warning in Intellij // unrechable } It’s hard to spot when using var instead of explicit type. In project, I’m working I found a piece of such bug in prod and test code. To force fixing such error, we coul...