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Spring / Spring gRPC Interview Questions

What is the difference between proto2 and proto3 syntax?

proto2 distinguishes required, optional, and repeated fields explicitly, and lets you customize default values per field.

proto3 simplified this: it dropped the required qualifier entirely (all singular fields behave as implicitly optional, taking a language-specific default such as 0, empty string, or empty list when unset), removed custom default values, and added first-class support for maps, the Any type, and native JSON mapping. Later proto3 revisions reintroduced an explicit optional keyword for scalar fields when a service genuinely needs to distinguish 'unset' from 'set to the default value.' Most current gRPC/Spring projects default to proto3 for its simpler, more forward-compatible model.

Which field qualifier did proto3 remove compared to proto2?
What was added back into later proto3 revisions to support explicit field-presence tracking?

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