Java学习－－Object类中的几个方法

Object是Java所有对象的基类，其中有几个方法，子类可以重写。

package equals;

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));
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());

}
}

package equals;

import java.time.LocalDate;
import java.util.Objects;

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

package equals;

public class Manager extends Employee{
private double bonus;

public Manager(String name, double salary, int year, int month, int day) {
super(name, salary, year, month, day);
// TODO Auto-generated constructor stub
bonus = 0;
}
public double getSalary() {
double baseSalary = super.getSalary();
return baseSalary + bonus;
}
public void setBonus(double bonus) {
this.bonus = bonus;
}
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 + "]";
}
}

输出：

alice1 == alice2: true

alice1 == alice3: false

al
4000
ice1.equals(alice3): true

alice1.equals(bob): false

boss.toString(): equals.Manager[name=Carl cracker,salary=80000.0,hireDay=1987-12-15][bonus=5000.0]

carl.equals(boss): false

alice1.hashCode(): -808853550

alice3.hashCode(): -808853550

bob.hashCode(): -624019882

carl.hashCode(): 1949236909