回答 4 已采纳 ```
public class EqualTest {
public static void main(String[] args) {
Employee alice1 = new Employee("Alice Adams", 75000, 1989, 12, 15);
Employee alice2 = alice1;
Employee alice3 = new Employee("Alice Adams", 75000, 1989, 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 car1 = 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): "+car1.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("car1.hashCode(): "+car1.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 boolean equals(Object otherObject){
//这里获得一个对象参数，第一个if语句判断两个引用是否是同一个，如果是那么这两个对象肯定相等
if(this == otherObject)
return true;
//这里判断这个参数是否引用空值
if(otherObject == null)
return false;
//getClass()方法是得到对象的类，这里就是如果两个对象的类不一样，那么就不相等
if(getClass()!=otherObject.getClass())
return false;
//在以上判断完成，再将得到的参数对象强制转换为该对象，考虑到父类引用子类的对象的出现，然后再判断对象的属性是否相同
Employee other = (Employee)otherObject;
return Objects.equals(name, other.name)&&salary ==other.salary&&
Objects.equals(hireDay, other.hireDay);
}
//哈希散列，有自己的计算方法，根据字符串来得到一段数字
public int hashCode(){
return Objects.hash(name,salary,hireDay);
}
//toString()方法，可自动生成
@Override
public String toString() {
return getClass().getName()+ "[name=" + name + ", salary=" + salary + ", hireDay=" + 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+"]";
}
}
```
这个程序里面有一部分，是public boolean equals（object otherObject）方法，
在这个方法的return语句里面莫名其妙的出现了一个Object.equals(a,b),我不明白这个是从哪里来的，求大神解释一下。
