AbstractEnumConverter.java

import java.util.concurrent.TimeUnit;

public class AbstractEnumConverter<T extends Enum<T>> {
  private final Class<T> enumClass;
  private final T[] values;

  protected AbstractEnumConverter(Class<T> enumClass) {
    assert enumClass.isEnum();
    this.enumClass = enumClass;
    this.values = enumClass.getEnumConstants();
  }
  
  public T fromInt(int idx) {
    return values[idx];
  }
}
class TimeUnitConverter extends AbstractEnumConverter<TimeUnit> {
  TimeUnitConverter() { super(TimeUnit.class);}
}