Java抽象类方法重写疑问：子类方法为何未按预期重写？

Hey there! I totally get the confusion—when you're just starting out with Java, abstract class inheritance and method overriding can throw you for a loop when things don't line up with what you expect. Let's walk through some of the most common reasons why your subclass method might not be acting as an override:

• Mismatched method signatures
  This is the #1 culprit. For a method to be an override, every part of the signature has to match exactly: parameter types, number of parameters, and even their order. Even tiny differences (like using Integer instead of int, or swapping two parameter types) mean it's a new overloaded method, not an override. Also, remember that return types need to be covariant—you can't return a String in the subclass if the abstract method returns an Object, but you can return a String if the abstract method returns a CharSequence.

• Static methods don't support overriding
  While abstract classes can have static methods, abstract methods themselves can't be static. If you're dealing with a static method in the abstract class, any "matching" static method in the subclass is just hiding the parent method, not overriding it. When you call a static method, Java uses the type of the reference (or the class name if you call it directly) to decide which method to run—no polymorphism here.

• Invalid access modifiers
  A subclass's overridden method can't have a stricter access modifier than the parent method. For example, if the abstract method is protected abstract void calculate(), your subclass can't make it private void calculate()—the compiler will flag this as an error. Double-check that your subclass method's access level is the same or more permissive (e.g., public instead of protected).

• Polymorphism isn't being triggered
  If you're calling the method from within a parent class constructor, or using a parent class reference but calling a static method, you won't get the subclass's overridden behavior. Also, if you're directly calling the method on the subclass class name (instead of an instance), you're bypassing polymorphism entirely.

If you can share the exact sample code you're looking at, I can break down exactly why the output is what it is. But start by checking these common pitfalls—chances are one of them is the issue!

内容的提问来源于stack exchange，提问作者Leff