Java Standard Library
The library people reimplement by hand: what split really returns, StringBuilder, Optional, streams and collectors, comparators, java.time, the Objects helpers and text blocks. Ten built-ins that already do the job, and one behaviour in each that is not the one you assumed.
Who it is for
Reaches for a dependency before the built-in.
The behaviour people get wrong after they are already productive in the language.
You will get the most out of it if you have written Java recently enough to read it without effort, and have been surprised by it at least once. If you are picking the language up for the first time, start with Java Essentials and come back to this one.
How long it takes
90 graded questions at roughly 45 seconds each is about 68 minutes of answering in total.
At the default five questions a day, and because the session mixes in your other courses, expect around 18 days — call it 3 weeks — to see everything once, plus a few weeks of thinning reviews after that before it is all mastered.
A question is mastered on the third correct answer, once the gap between reviews has grown past a week — so a course cannot be finished in a weekend however long you sit with it.
Question mix
- 60 multiple choice
- 10 concept cards
- 10 predict the output
- 10 put it in order
- 10 matching questions
Syllabus
What you will be asked about
-
01
What split Really Returns
Predict how many pieces split gives you, and say when an empty field survives.
-
02
Cleaning and Comparing
Choose between trim and strip, and read what isBlank, repeat and compareTo return.
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03
Building Strings
Explain what + compiles into, and use StringBuilder where concatenation would cost you.
-
04
Optional, Properly
Use Optional as a return value, and name the three ways it gets abused.
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05
Stream Pipelines
Trace when a stream actually runs, and say what a terminal operation does to it.
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06
Collectors
Assemble stream results with groupingBy, joining and toMap, and avoid their sharp edges.
-
07
Comparators
Compose a sort key with comparing and thenComparing, and predict what reversed reverses.
-
08
Dates Without Surprises
Do arithmetic on LocalDate, and choose between Period and Duration.
-
09
Objects and Null
Use the Objects helpers to write null-safe code without a cascade of if statements.
-
10
Text Blocks and Formatting
Predict what a text block contains, and format numbers without a locale surprise.
8 more topics, and all 90 questions
Java Standard Library is a Pro course. One subscription opens it and every other course in the catalogue, including the ones still being written.
A question from this course
What split Really Returns
What does this print?
public class Main {
public static void main(String[] args) {
System.out.println("a,b,,".split(",").length);
}
}Show the answer
A 2
You may have expected 4 because there are four fields marked out by those commas. split with one argument uses limit 0, and limit 0 deletes every empty string at the end of the array, so both tail fields vanish. The array you get back is [a, b].
The rest of the track
Java at every depth
Java Essentials
The behaviour underneath the ceremony: what a variable really holds, why 1/2 is 0, and why two Strings that look identical are not always the same object. Ten spines on the code that compiles cleanly and still does something else.
Java Core
Where Java trips developers who use it every day: autoboxing that hides a NullPointerException, a ternary that quietly unboxes, and dispatch rules that pick a method before the program runs. Ten spines on the gap between what the code says and what the JVM does.
Java Data & Collections
The collections framework taken seriously: which container promises what, why remove(1) deletes a position, and how a mutated key disappears from its own HashMap. Ten spines on the containers you use every day and the contracts underneath them.
Java Errors & Edge Cases
Exceptions at the points where they stop behaving the way you assumed: a finally block that discards the exception unwinding through it, a map lookup that throws on the way into an int, a class that fails once and reports a missing definition forever after. Ten spines on the paths your happy-path code never takes.
Java Idioms & Pitfalls
The Java people write out of habit that is wrong or dated: raw types, boxed equality, catching Exception, building strings in a loop, arrays where a List belongs and getters that hand out the field. Ten habits, each one run to see what it actually does.
Java Advanced
The traps a confident Java reader still walks into: erasure, wildcard variance, dispatch decided before the program runs, and a constructor that sees a field before it is assigned. Ten spines of code that compiles cleanly and behaves otherwise.
Java Performance
What actually costs on the JVM, read off code rather than a stopwatch: the allocation that never happens, the concat loop that copies everything twice, the map that rehashes sixteen times on its way to a million entries. Ten spines on the difference between the operation you wrote and the work the VM does.
Java Testing
What a Java test actually asserts, and where that claim is weaker than it looks. Argument order and failure messages, the three kinds of equality, deltas, throwing, fixtures and static state, test doubles, and the difference between a failure and an error.
Java Interview Questions
The Java an interviewer actually probes, answered from the rules rather than from memory. The equals and hashCode contract, the string pool, references and boxing, collections, erasure, checked exceptions, dispatch, immutability, and the what-does-this-print questions behind them.
Start Java Standard Library
in tomorrow’s session.
Enrol and this course joins your daily five, mixed in with everything else you are studying — 90 questions spread over about 18 days rather than dropped on you at once.
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