PhoneNumber.java

// Making PhoneNumber comparable - Pages 65-66
package org.effectivejava.examples.chapter03.item12;

import java.util.NavigableSet;
import java.util.Random;
import java.util.TreeSet;

public final class PhoneNumber implements Cloneable, Comparable<PhoneNumber> {
	private final short areaCode;
	private final short prefix;
	private final short lineNumber;

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

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

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

	@Override
	public int hashCode() {
		int result = 17;
		result = 31 * result + areaCode;
		result = 31 * result + prefix;
		result = 31 * result + lineNumber;
		return result;
	}

	/**
	 * Returns the string representation of this phone number. The string
	 * consists of fourteen 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".
	 * 
	 * Note that there is a single space separating the closing parenthesis
	 * after the area code from the first digit of the prefix.
	 */
	@Override
	public String toString() {
		return String.format("(%03d) %03d-%04d", areaCode, prefix, lineNumber);
	}

	@Override
	public PhoneNumber clone() {
		try {
			return (PhoneNumber) super.clone();
		} catch (CloneNotSupportedException e) {
			throw new AssertionError(); // Can't happen
		}
	}

	// Works fine, but can be made faster
	// public int compareTo(PhoneNumber pn) {
	// // Compare area codes
	// if (areaCode < pn.areaCode)
	// return -1;
	// if (areaCode > pn.areaCode)
	// return 1;
	//
	// // Area codes are equal, compare prefixes
	// if (prefix < pn.prefix)
	// return -1;
	// if (prefix > pn.prefix)
	// return 1;
	//
	// // Area codes and prefixes are equal, compare line numbers
	// if (lineNumber < pn.lineNumber)
	// return -1;
	// if (lineNumber > pn.lineNumber)
	// return 1;
	//
	// return 0; // All fields are equal
	// }

	public int compareTo(PhoneNumber pn) {
		// Compare area codes
		int areaCodeDiff = areaCode - pn.areaCode;
		if (areaCodeDiff != 0)
			return areaCodeDiff;

		// Area codes are equal, compare prefixes
		int prefixDiff = prefix - pn.prefix;
		if (prefixDiff != 0)
			return prefixDiff;

		// Area codes and prefixes are equal, compare line numbers
		return lineNumber - pn.lineNumber;
	}

	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);
	}

	private static final Random rnd = new Random();

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