有关equals()方法的疑问

[sunyuqian]

大家好，这是一道java2核心技术的例题，有一些地方不明白，用/*...*/标出，请高手解答

import java.util.*;

public class EqualsTest
{
	public static void main(String[] args)
	{
		Employee alice1 = new Employee("Alice Adams",75000,1987,12,15);
		Employee alice2 = alice1;
		Employee alice3 = new Employee("Alice Adams",75000,1987,12,15);
		Employee bob = new Employee("Bob Brandson",50000,1989,10,1);
		System.out.println("alice1 == alice2: "+(alice1 == alice2));
		System.out.println("alice1 == alice3: "+(alice1 == alice3));
		System.out.println("alice1.equals(alice3): "+alice1.equals(alice3));
		System.out.println("alice1.equals(bob) "+alice1.equals(bob));
		System.out.println("bob.toString(): "+bob);
		Manager carl = new Manager("Carl Craker",80000,1987,12,15);
		Manager boss = new Manager("Carl Craker",80000,1987,12,15);
		boss.setBonus(5000);
		System.out.println("boss.toString(): "+boss);

		System.out.println("carl.equals(boss): "+carl.equals(boss));/*为什么这显示的是false,而不是true。上面alice1.equals(alice3)显示的就是 true*/

		System.out.println("alice1.hashCode(): "+alice1.hashCode());
		System.out.println("alice3.hashCode(): "+alice3.hashCode());
		System.out.println("bob.hashCode(): "+bob.hashCode());
		System.out.println("carl.hashCode(): "+carl.hashCode());
	}
}

class Employee
{
	public Employee(String n,double s,int year,int month,int day)
	{
		name=n;
		salary=s;
		GregorianCalendar Calendar = new GregorianCalendar(year,month-1,day);
		hireDay = Calendar.getTime();
	}

	public String getName()
	{
		return name;
	}

	public double getSalary()
	{
		return salary;
	}

	public Date getHireDay()
	{
		return hireDay;
	}

	public void raiseSalary(double byPercent)
	{
		double raise = salary * byPercent/100;
		salary+=raise;
	}

	public boolean equals(Object otherObject)
	{
		if(this == otherObject)
			return true;
		if(otherObject == null)
			return false;
		if(getClass()!=otherObject.getClass())
			return false;
		Employee other = (Employee)otherObject;
			return name.equals(other.name)&&salary == other.salary&&hireDay.equals(other.hireDay);
	}

	public int hashCode()
	{
		return 7*name.hashCode()+11*new Double(salary).hashCode()+13*hireDay.hashCode();
/*加这些数字有什么作用，7，11，13，是固定的吗*/
	}

	public String toString()
	{
		return getClass().getName()+"[name="+name+",salary="+salary+",hireDay="+hireDay+"]";
	}

	private String name;
	private double salary;
	private Date hireDay;
}

class Manager extends Employee
{
	public Manager(String n,double s,int year,int month,int day)
	{
		super(n,s,year,month,day);
		bonus=0;
	}
	
	public double getSalary()
	{
		double baseSalary = super.getSalary();
		return baseSalary+bonus;
	}
	
	public void setBonus(double b)
	{
		bonus = b;
	}

	public boolean equals(Object otherObject)
	{
		if(!super.equals(otherObject))
			return false;
		Manager other = (Manager)otherObject;
			return bonus == other.bonus;
	}

	public int hashCode()
	{
		return super.hashCode()+17*new Double(bonus).hashCode();
	}

	public String toString()
	{
		return super.toString()+"[bonus="+bonus+"]";
	}

	private double bonus;
}

[Acylas]

那些数字不是固定，只是编程的人定义一个规则生成的hashcode保证不会和其他不同employee重复即可，比如也可以用employee对应员工的身份证号码作为hashcode

[捏造的信仰]

汗死，你自己不是写了一句：boss.setBonus(5000);吗？两个对象的 bonus 不相等了，判断结果当然是 false 了

[sunyuqian]

谢谢了