方法可以访问调用这个方法的对象的私有数据。一个方法可以访问所属类的所有对象的私有数据。

class Employee{
    ...
    @Override
    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 fields have identical values
        return Objects.equals(name, other.name)
                && salary == other.salary
                && Objects.equals(hireDay, other.hireDay);
    }
}

public class Manager extends Employee {
    ...
}

典型的调用方式是：

Employee harry = new Employee("Harry Hacker", 50000, 1989, 10, 1);
Manager boss = new Manager("Carl Cracker", 75000, 1987, 12, 15);

if(harry.equals(boss))...

这个 equals 方法访问 harry 的私有字段，这点并不会让人奇怪，不过，它还访问了 boss 的私有字段。这是合法的，其原因是 boss 是 Employee 类型对象，而 Employee 类的方法可以访问任何 Employee 类型对象的私有字段。