Java中为何方法重载属静态多态？异名同类方法为何不算多态？

Great question—this is a super common point of confusion when getting to grips with polymorphism in Java. Let's break this down clearly, using your code as a reference.

First, let's recap what static/compile-time polymorphism actually means:

• It’s a form of polymorphism where the JVM knows exactly which method to call at compile time (before the program runs).
• Most importantly, it centers around using the same method name to represent the same general behavior, with different implementations based on input parameters.

Why polymorphicMethod qualifies as static polymorphism #

Your polymorphicMethod overloads check both boxes perfectly:

1. Shared method name, shared intent: All three versions of polymorphicMethod use the same name because they represent the same core action (like processing some input)—the only difference is what kind of input they accept. This is the heart of polymorphism: one interface, multiple implementations.
2. Compile-time binding: When you call polymorphicMethod in your code, the compiler looks at the type, number, and order of arguments you pass, then immediately picks the matching overload. This decision is locked in before the program runs, which is why it’s called "static" or "compile-time" polymorphism.

For example:

StaticPolymorphismSample obj = new StaticPolymorphismSample();
obj.polymorphicMethod(42);          // Compiler binds to the int-only version
obj.polymorphicMethod(42, 100);     // Binds to the two-int version
obj.polymorphicMethod("Hello");     // Binds to the String version

Notice how you use the same method name to trigger different behaviors—this is the polymorphic behavior in action.

Why nonPolymorphicMethod and nonPolymorphicMethod1 are not polymorphic #

These methods fail the core requirements of polymorphism, even though their parameter lists are similar:

1. Different method names = different behaviors: nonPolymorphicMethod and nonPolymorphicMethod1 are entirely separate methods. Their different names signal to the compiler (and to developers) that they represent distinct actions, not variations of the same action. Polymorphism relies on reusing a single name to abstract similar behaviors.
2. No compile-time association: In Java, a method's identity is defined by its full signature: method name + parameter list. Since these two methods have different names, they’re treated as completely independent—there’s no link between them that qualifies as "polymorphism". Calling one vs. the other requires explicitly using different names, which means there’s no "one interface, multiple implementations" benefit here.

To sum it up: The key difference isn’t just about parameter lists—it’s about whether the methods are grouped under the same name to represent a unified behavior. Overloading lets you abstract similar operations behind a single name, which is exactly why it’s considered a form of static polymorphism.异名方法 don’t offer that abstraction, so they’re just regular, unrelated methods.

内容的提问来源于stack exchange，提问作者Hayk Melkonyan