package cn.xf.cp.ch02.item9;

import java.util.HashMap;

import java.util.Map;

public class 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

    //至于为什么使用31，这个是推荐值，研究表明这个数字用起来性能比较好

    public int hashCode()

    {

        int result = 17;

        result = 31 * result + areaCode;

        result = 31 * result + prefix;

        result = 31 * result + lineNumber;

        return result;

    }

    */

    //如果一个对象不是经常变动，而且开销比较大的话，就要考虑吧散列码缓存在对象内部

    //用volatile修饰的变量，线程在每次使用变量的时候，都会读取变量修改后的最的值。

    private volatile int hashcode;

    @Override

    public int hashCode()

    {

        int result = hashcode;

        if (result == 0)

        {

            result = 17;

            result = 31 * result + areaCode;

            result = 31 * result + prefix;

            result = 31 * result + lineNumber;

            hashcode = result;

        }

        return result;

    }

    public static void main(String[] args)

    {

        Map<PhoneNumber, String> m = new HashMap<PhoneNumber, String>();

        m.put(new PhoneNumber(707, 867, 5309), "Jenny");

        //这里不会返回jenny哦，会返回null，这个是因为put对象吧他们放到不同的散列桶中

        System.out.println(m.get(new PhoneNumber(707, 867, 5309)));

    }

}