There are some places in JDK code base where we call Enum.class.getEnumConstants() to get all the values of the enum. This is excessive, less-readable and slower than just calling values() method as in getEnumConstants() we have a volatile access:

public T[] getEnumConstants() {
    T[] values = getEnumConstantsShared();
    return (values != null) ? values.clone() : null;
}

private transient volatile T[] enumConstants;

T[] getEnumConstantsShared() {
    T[] constants = enumConstants;
    if (constants == null) { }
    return constants;
}

Calling values() method is slightly faster:

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"})
public class EnumBenchmark {

  @Benchmark
  public Enum[] values() {
    return Enum.values();
  }

  @Benchmark
  public Enum[] getEnumConstants() {
    return Enum.class.getEnumConstants();
  }

  private enum Enum {
    A,
    B
  }
}

Benchmark Mode Cnt Score Error Units
EnumBenchmark.getEnumConstants avgt 15 6,265 ± 0,051 ns/op
EnumBenchmark.getEnumConstants:·gc.alloc.rate avgt 15 2434,075 ± 19,568 MB/sec
EnumBenchmark.getEnumConstants:·gc.alloc.rate.norm avgt 15 24,002 ± 0,001 B/op
EnumBenchmark.getEnumConstants:·gc.churn.G1_Eden_Space avgt 15 2433,709 ± 70,216 MB/sec
EnumBenchmark.getEnumConstants:·gc.churn.G1_Eden_Space.norm avgt 15 23,998 ± 0,659 B/op
EnumBenchmark.getEnumConstants:·gc.churn.G1_Survivor_Space avgt 15 0,009 ± 0,003 MB/sec
EnumBenchmark.getEnumConstants:·gc.churn.G1_Survivor_Space.norm avgt 15 ≈ 10⁻⁴ B/op
EnumBenchmark.getEnumConstants:·gc.count avgt 15 210,000 counts
EnumBenchmark.getEnumConstants:·gc.time avgt 15 119,000 ms

EnumBenchmark.values avgt 15 4,164 ± 0,134 ns/op
EnumBenchmark.values:·gc.alloc.rate avgt 15 3665,341 ± 120,721 MB/sec
EnumBenchmark.values:·gc.alloc.rate.norm avgt 15 24,002 ± 0,001 B/op
EnumBenchmark.values:·gc.churn.G1_Eden_Space avgt 15 3660,512 ± 137,250 MB/sec
EnumBenchmark.values:·gc.churn.G1_Eden_Space.norm avgt 15 23,972 ± 0,529 B/op
EnumBenchmark.values:·gc.churn.G1_Survivor_Space avgt 15 0,017 ± 0,003 MB/sec
EnumBenchmark.values:·gc.churn.G1_Survivor_Space.norm avgt 15 ≈ 10⁻⁴ B/op
EnumBenchmark.values:·gc.count avgt 15 262,000 counts
EnumBenchmark.values:·gc.time avgt 15 155,000 ms