The answer is quite easy, if you find the Stream API of Java 8. These API supports functional-style operations on streams of elements, such as map-reduce transformations on collections.

So in Javascript the code would be like:

const transformedCtas = section.elements.cta.value.map(cta => ({
    ctaTitle: cta.elements.title.value,
    ctaUrl: cta.elements.external_url.value
}));

In Java 8, you would use:

List<CTA> transfomedCtas = section
    .getElements()
    .getCta() // This returns List/Enumerable/...
    .stream() // This is the key - transform data to sream and then use strem API for whatever you want
    .map(cta -> 
        new CTA(cta.getElements().getTitle(), cta.getElements().getExternalUrl()
    );