PhoneNumber.java

package effectivejava.chapter3.item14;
import java.util.*;
import java.util.concurrent.ThreadLocalRandom;
import static java.util.Comparator.*;

// Making PhoneNumber comparable (Pages 69-70)
public final class PhoneNumber implements Cloneable, Comparable<PhoneNumber> {
    private final short areaCode, prefix, lineNum;

    public PhoneNumber(int areaCode, int prefix, int lineNum) {
        this.areaCode = rangeCheck(areaCode, 999, "area code");
        this.prefix   = rangeCheck(prefix,   999, "prefix");
        this.lineNum  = rangeCheck(lineNum, 9999, "line num");
    }

    private static short rangeCheck(int val, int max, String arg) {
        if (val < 0 || val > max)
            throw new IllegalArgumentException(arg + ": " + val);
        return (short) val;
    }

    @Override public boolean equals(Object o) {
        if (o == this)
            return true;
        if (!(o instanceof effectivejava.chapter3.item11.PhoneNumber))
            return false;
        PhoneNumber pn = (PhoneNumber)o;
        return pn.lineNum == lineNum && pn.prefix == prefix
                && pn.areaCode == areaCode;
    }

    @Override public int hashCode() {
        int result = Short.hashCode(areaCode);
        result = 31 * result + Short.hashCode(prefix);
        result = 31 * result + Short.hashCode(lineNum);
        return result;
    }

    /**
     * Returns the string representation of this phone number.
     * The string consists of twelve characters whose format is
     * "XXX-YYY-ZZZZ", where XXX is the area code, YYY is the
     * prefix, and ZZZZ is the line number. Each of the capital
     * letters represents a single decimal digit.
     *
     * If any of the three parts of this phone number is too small
     * to fill up its field, the field is padded with leading zeros.
     * For example, if the value of the line number is 123, the last
     * four characters of the string representation will be "0123".
     */
    @Override public String toString() {
        return String.format("%03d-%03d-%04d",
                areaCode, prefix, lineNum);
    }

//    // Multiple-field Comparable with primitive fields (page 69)
//    public int compareTo(PhoneNumber pn) {
//        int result = Short.compare(areaCode, pn.areaCode);
//        if (result == 0)  {
//            result = Short.compare(prefix, pn.prefix);
//            if (result == 0)
//                result = Short.compare(lineNum, pn.lineNum);
//        }
//        return result;
//    }

    // Comparable with comparator construction methods (page 70)
    private static final Comparator<PhoneNumber> COMPARATOR =
            comparingInt((PhoneNumber pn) -> pn.areaCode)
                    .thenComparingInt(pn -> pn.prefix)
                    .thenComparingInt(pn -> pn.lineNum);

    public int compareTo(PhoneNumber pn) {
        return COMPARATOR.compare(this, pn);
    }

    private static PhoneNumber randomPhoneNumber() {
        Random rnd = ThreadLocalRandom.current();
        return new PhoneNumber((short) rnd.nextInt(1000),
                               (short) rnd.nextInt(1000),
                               (short) rnd.nextInt(10000));
    }

    public static void main(String[] args) {
        NavigableSet<PhoneNumber> s = new TreeSet<PhoneNumber>();
        for (int i = 0; i < 10; i++)
            s.add(randomPhoneNumber());
        System.out.println(s);
    }
}