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Dennis LIVE Senior Java Software Engineer · 11 yrs industry responds ≤ 4 h Free first conversation →
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// equals + hashCode go together @Override public boolean equals(Object o) { if (this == o) return true; if (!(o instanceof User u)) return false; return id.equals(u.id); }
We start where you stand, not where the syllabus begins. Pick your profile to see the typical topic map. In the first chat we adapt it to you.
An anonymised forum post from a tutoring hour, and how Dennis answered it. So you can see how deep and concrete an explanation gets.
public boolean equals(Object o) {
Buch other = (Buch) o;
return this.titel.equals(other.titel);
} In the test someone calls new Buch("Effi").equals(null). Should return false, but crashes. I heard something about a „contract" in the lecture, but I do not get what is wrong here.
Three bugs at once, classic equals trap. Let us walk through them:
The equals contract says: x.equals(null) must return false, never throw. First line in the method body: if (o == null) return false;
If someone calls buch.equals("Effi"), the cast (Buch) o blows up as a ClassCastException. Check with getClass() or instanceof first.
Even if o is a Buch: if your own titel is null, NPE in this.titel.equals(...). Fix: Objects.equals(this.titel, other.titel).
@Override
public boolean equals(Object o) {
if (o == null || getClass() != o.getClass()) return false;
Buch other = (Buch) o;
return Objects.equals(this.titel, other.titel);
} Rule of thumb: equals always follows the same shape. 1) null? 2) same class? 3) compare fields with Objects.equals(). And ALWAYS override hashCode() when you override equals(), otherwise you break HashMap and HashSet.
From first Hello World to Spring Boot REST APIs. We focus on what is actually tested or used in your context, not on every paragraph of the syllabus.
Variables, control flow, methods, arrays, collections, exceptions. The foundation Programming I builds on.
Classes, objects, inheritance, polymorphism, interfaces. The block most exams hinge on.
Lists, maps, sets, trees, sorting, searching. Big-O made practical, not just academic.
Generics, the Stream API, lambdas, JUnit. The level expected in industry and in advanced exams.
Spring Boot, REST APIs, JDBC, JPA. From a Hello World controller to a small production backend.
Past papers, IHK project work, oral exams. We work on the artefacts you will be graded on.
I built Study IT because I have seen first-hand how computer-science teaching at university falls apart.
Our tutors are working developers, not student side-jobbers.
Reach me directly: marcel.schmidtpeter@study-it.education
Dennis ist unser Java-Spezialist: Senior Java Software Engineer mit 11 Jahren Industrieerfahrung. Java, Spring, C# und Python aus echten Projekten, nicht aus Tutorials.
„Programmieren versteht man, wenn man weiß, warum eine Lösung funktioniert. Mein Ziel: dass du Code nicht abschreibst, sondern selbst hinkriegst."
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First chat plus first paid hour: where do you stand, where are the gaps, what is the actual goal?
OOP, methods, control flow, arrays. We patch the basics so the rest can stack on top.
Streams, generics, Spring, JDBC: whatever your exam or project asks. On your real code.
Past papers, mock interview, IHK project rehearsal. Tested under time, with honest feedback.
Three related programmes that share the same 1:1 senior-dev approach.
15 minutes to talk, then you decide. NPE, equals, streams: whatever is blocking you, we walk through it live.