RFR: 6588: Move JMC core to JDK 8

[Marcus Hirt]

On Wed, 20 Jan 2021 14:18:14 GMT, Marcus Hirt <hirt at openjdk.org> wrote:

>> @thegreystone Hi Marcus! The changes I've seen so far are to make use of JDK 8 language features where the overall functionality/result is the same. Are there any parts of the code where functionality is changed that might need a closer look?
>
> @jiekang - this is mostly a first step to make IItemCollection and friends more streaming friendly for consumers of core. There is also an API name change getTimeRanges -> getAvailableTimeRanges (for API introduced in 8, so should be OK). I'm thinking we might be able to perhaps find a better name there. It's all of the available time ranges in the recording, not necessarily only for the filtered collection. getOriginalTimeRanges?

Recording is not good, since IItemCollections can be used outside of JFR in the future.

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PR: https://git.openjdk.java.net/jmc/pull/194