equals方法

[longer5153458]

package next11;

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



public class EmployeeTest {
	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);
		
		
		
	}
}

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 Date getHireDay() {
		return hireDay;
	}
	public String getName() {
		return name;
	}
	public double getSalary() {
		return salary;
	}
	public void raiseSlary(double byPercent){
		double raiseSalary = salary*byPercent/100;
		salary +=raiseSalary;
	}
	
	public boolean equals (Object otherObject){
		if(this == otherObject) return true;//这一句要怎么理解？本类对象与otherObject引用的对象一致？alice1.equals(alice3)套上的话又该怎么具体分析呢？
											//Object otherObject = alice3？如果是这样，所指的对象应该不同呀。有点卡住了，呵呵
		if(otherObject==null) return false;
		if(this.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();
	}
	
	public String toString(){
		return getClass().getName()
				+"[name="+name
				+",salary="+salary
				+",hireDay="+hireDay
				+"]";
	}
	
}

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 super.getSalary()+baseSalary;
	}
	
	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
				+"]";
	}
	
	
	
	
}

[oh_Maxy]

equals有如下特性： 1. 自等（就是自己equals自己，结果为true，你的疑问解决了吧：this表示本对象） 2. 对称（a equals b，那么b equals a） 3. 传递（a equals b, b equals c, 那么a equals c） 4. 根据惯例，还有个非空（不能与null相等）

[longer5153458]

引用

那句相当于本类引用对象和参数引用对象哈希码相同，也就是地址相同，指向同一个对象实例 重写的equals方法是先比较引用对象alice1与alice3的哈希码，如果相同返回true，如果不同再继续比较他们的对象实例，实例相同也返回true

"=="不是要求所引用的对象必须是同一个才是true么？ if(this == otherObject) return true;我是这么理解的：Object otherObject = alice3;（otherObject引用alice3的对象）然后alice1=otherObject（很明不是同一对象）所以应该返回false。但这是错的，我就是不知道我错在哪里？

[Logical_butterfly]

那句相当于本类引用对象和参数引用对象哈希码相同，也就是地址相同，指向同一个对象实例 重写的equals方法是先比较引用对象alice1与alice3的哈希码，如果相同返回true，如果不同再继续比较他们的对象实例，实例相同也返回true