# collections

Companion code for the ankurm.com post *"How to Sort a HashMap by Value (and Key) in Java."*
Module `collections` in `java-core-examples`.

All explanation lives in the post; this module holds the runnable evidence and the captured output.

## Versions

| Component | Version |
|---|---|
| JDK | 25.0.4.1+1 (Temurin, LTS) |
| JMH | 1.37 |
| JUnit Jupiter | 5.11.0 |
| Hardware | 2 vCPU x86-64 VM, shared with other jobs (timings are indicative, not a leaderboard) |

## Quickstart

```bash
export JDK25_HOME=/path/to/jdk-25
./scripts/run-all.sh        # rebuilds and regenerates everything in output/
```

## What is in here

| File | Shows | Output |
|---|---|---|
| `SortByValueDemo` | stream into `LinkedHashMap`, descending, by key, list of entries, the `toMap()` default-HashMap trap, tie-break | `01` |
| `TieBugDemo` | a `TreeMap` with a value-only comparator silently drops equal values; the tie-break fix | `02` |
| `TopNDemo` | top-N by sort+limit and by a size-N `PriorityQueue` | `03` |
| `SequencedDemo` | JDK 21+ `reversed()`, `firstEntry()`, `putLast()`, live-view behaviour | `04` |
| `src/broken/*.java` | `HashMap` has no `firstEntry()`; `Collections.sort(map)` does not compile; javac's real message is captured | `05`-`06` |
| `SortingBenchmark` | JMH: sort-all vs heap top-10 at 1,000 and 100,000 entries; full sort into `LinkedHashMap` | `07` |
| `SortingTest` | 6 assertions behind the claims above | `08` |

The JMH run is 2 forks, 3 warmup and 5 measurement iterations of 2 s per fork. The sandbox it ran on
was shared with other jobs, so re-running moves the numbers by tens of percent but not the ordering.