How I learn Java

Some people call C# a slightly better Java. I am well experienced in C# but Java is a new language to me. I started using Java since August last year, 2023. It's an interesting journey for me to learn Java. In my mental model, the code I want to write exists. It's not C# or Java, yet it's closer to C# as C# is like my native programming language. I think in terms of JavaScript more often these days though. When I work on my projects, I translate the code in my mind into Java. This post is about the translation. It happens instantly sometimes as it's obvious. Sometimes, I have to google or ask LLM to help.

Add null value to a list

Tue. 23/4/2024

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given(resource.predict(argThat(argumentMatcher())))
    .willReturn(Arrays.asList(null, new BigDecimal("0.7"), null, new BigDecimal("0.5")));

• A typical way of creating a list with a given value is List.of(new BigDecimal("0.7"))
• List.of() doesn't allow null as argument
• Use Arrays.asList() if you want to insert a null value

Filter out null values from a list

Tue. 23/4/2024

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private <T> Optional<T> getPrediction(List<T> predictions) {
	if (predictions == null) {
		return Optional.empty();
	}

	return predictions.stream()
		.filter(Objects::nonNull)
		.findFirst();
}

• To use lambda function, you call stream() on the collection. Stream in Java is a sequence of elements supporting sequential and parallel aggregate operations. C# doesn't require stream(). All collections support aggregate operations by default.
• Objects::nonNull is a method reference and used as a predicate in the filter operation