PhoneNumber.java

package effectivejava.chapter3.item13;

import java.util.HashMap;
import java.util.Map;

// Adding a clone method to PhoneNumber (page 59)
public final class PhoneNumber implements Cloneable {
    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 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);
    }

    // Clone method for class with no references to mutable state (Page 59)
    @Override public PhoneNumber clone() {
        try {
            return (PhoneNumber) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new AssertionError();  // Can't happen
        }
    }

    public static void main(String[] args) {
        PhoneNumber pn = new PhoneNumber(707, 867, 5309);
        Map<PhoneNumber, String> m = new HashMap<>();
        m.put(pn, "Jenny");
        System.out.println(m.get(pn.clone()));
    }
}