java类中的equals、hashCode和toString方法

程序实现了Employee类和Manager类的equals、hashCode和toString方法。

程序如下：

public class EqualsTest
{
	public static void main(String[] args)
	{
		Employee alice1 = new Employee("Alice Adamas", 75000, 1987, 12, 15);
		Employee alice2 = alice1;
		Employee alice3 = new Employee("Alice Adamas", 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());
		System.out.println("boss.hashCode(): " + boss.hashCode());
	}
}

import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Objects;

public class Employee
{
	private String name;
	private double salary;
	private Date hireDay;
	
	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 int hashCode()
	{
		return Objects.hash(name, salary, hireDay);
	}
	
	public String toString()
	{
		return getClass().getName() + "[name=" + name + ",salary=" + salary + ",hireDay=" + hireDay + "]";
	}
	
	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 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 Objects.equals(name, other.name) && salary == other.salary && Objects.equals(hireDay, other.hireDay);
	}
}

public class Manager extends Employee
{
	private double bonus;
	
	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 + "]";
	}
}

编译并运行程序，结果见图1。

                                                                                            图1