Equals 和 hashcode 经典代码

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 Cracker", 80000, 1987, 12,
15);

Manager boss = new Manager("Carl Cracker", 80000, 1987, 12,
15);

boss.setBonus(5000);

System.out.println("boss.toString(): " + boss);

System.out.println("carl.equals(boss): " +
carl.equals(boss));

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)
{
// a
quick test to see if the objects are identical
if
(this == otherObject) return true;

//
must return false if the explicit parameter is null
if
(otherObject == null) return false;

// if
the classes don't match, they can't be equal
if
(getClass() != otherObject.getClass()) return false;

//
now we know otherObject is a non-null Employee

Employee other = (Employee) otherObject;

//
test whether the fields have identical values

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();
}

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;
//
super.equals checked that this and other belong to the same
class

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;
}