一文读懂《Effective Java》第19条：接口只用于定义类型

public interface PhysicalConstantsInterface {
  static final double AVOGADROS_NUMBER = 6.02214199e23;

  static final double BOLTZMANN_CONSTANT = 1.3806503e-23;

  static final double ELECTRON_MASS = 9.10938188e-31;
}

/**
 * Constants written into the Object Serialization Stream.
 *
 * @author  unascribed
 * @since JDK 1.1
 */
public interface ObjectStreamConstants {

    /**
     * Magic number that is written to the stream header.
     */
    final static short STREAM_MAGIC = (short)0xaced;

    /**
     * Version number that is written to the stream header.
     */
    final static short STREAM_VERSION = 5;

    /* Each item in the stream is preceded by a tag
     */

    /**
     * First tag value.
     */
    final static byte TC_BASE = 0x70;
}

public final class Integer extends Number implements Comparable<Integer> {
    /**
     * A constant holding the minimum value an {@code int} can
     * have, -2<sup>31</sup>.
     */
    @Native public static final int   MIN_VALUE = 0x80000000;

    /**
     * A constant holding the maximum value an {@code int} can
     * have, 2<sup>31</sup>-1.
     */
    @Native public static final int   MAX_VALUE = 0x7fffffff;
}

public class PhysicalConstants {
  static final double AVOGADROS_NUMBER = 6.02214199e23;

  static final double BOLTZMANN_CONSTANT = 1.3806503e-23;

  static final double ELECTRON_MASS = 9.10938188e-31;
}

import static effectivejava.no19.PhysicalConstants.AVOGADROS_NUMBER;
public class Test {
  double atoms(double mols){
    return AVOGADROS_NUMBER * mols;
  }
}