class A { }
class B extends A { }
Object o1 = new A();
Object o2 = new B();
o1 instanceof A => true
o1 instanceof B => false
o2 instanceof A => true // <================ HERE
o2 instanceof B => true
o1.getClass().equals(A.class) => true
o1.getClass().equals(B.class) => false
o2.getClass().equals(A.class) => false // <===============HERE
o2.getClass().equals(B.class) => true
getClass() will be useful when you want to make sure your instance is NOT a subclass of the class you are comparing with.
一個非常完美的equals方法的寫法：
// 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 name.equals(other.name) && salary == other.salary && hireDay.equals(other.hireDay);
}
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