在這個示例中示範的是 相等測試與繼承+Hashcode+toString
具體的代碼及運作結果如下:
Console如下:
alice1 == alice2: true
alice1 == alice3: false
alice1.equals(alice3): true
alice1.equals(bob): false
bob.toString(): Employee[name=Bob Brandson,salary=50000.0,hireDay=Sun Oct 01 00:00:00 CST 1989]
boss.toString(): Manager[name=carl Cracker,salary=80000.0,hireDay=Tue Dec 15 00:00:00 CST 1987][bonus=5000.0]
carl.toString(): Manager[name=Carl Cracker,salary=80000.0,hireDay=Tue Dec 15 00:00:00 CST 1987][bonus=0.0]
carl.equals(boss): false
alice1.hashCode(): 377780067
alice3.hashCode(): 377780067
bob.hashCode(): 955285015
carl.hashCode(): 386513600
boss.hashCode(): 510031328
如上所示:現在的問題是(見紅色字型),求大牛指導!
System.out.println("alice1.equals(alice3): " + alice1.equals(alice3)); //運作結果為:alice1.equals(alice3): true
System.out.println("carl.equals(boss): " + carl.equals(boss)); //但是這句的結果是:carl.equals(boss): false 這裡為什麼會使false? 求解答
import java.util.Date;
import java.util.GregorianCalendar;
public class EqualsTest {
/**
* @author cruise 2013-3-23 22:11
*
*
*/
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.toString(): " + carl);
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());
}
}
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 feilds 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;
}