CODEWITHSUNDEEP
javareflection
Jeremy Bi
Jeremy Bi

Reputation: 21

reflection api give overloading on function's return type

I am using reflection APIs to do some queries on Java methods. Below is the code snippet to find out the return type of calling, say new java.lang.StringBuilder().append('a'):

Class<?> c = Class.forName("java.lang.StringBuilder");
Method[] mList = c.getMethods();

for (int i = 0; i < mList.length; i++) {
    if (mList[i].getName() == "append" 
          && mList[i].getParameterTypes().length == 1 
          && mList[i].getParameterTypes()[0].getCanonicalName() == "char") {
        System.out.println(mList[i]);
    }
}

Oddly, the output gives

public java.lang.AbstractStringBuilder java.lang.StringBuilder.append(char)

public java.lang.Appendable java.lang.StringBuilder.append(char) throws java.io.IOException

public java.lang.StringBuilder java.lang.StringBuilder.append(char)

while the Java API Specification only gives StringBuilder as the return type. Does that mean the method append actually overloads on return type?

Upvotes: 2

Views: 63

Answers (2)

Konstantin Yovkov
Konstantin Yovkov

Reputation: 62864

When you invoke c.getMethods() the resulting array will contain all the methods, that are defined in the StringBuilder class and it superclass(es)/superinterface(s).

That's why you get three instead of one.

Does that mean the method append actually overloads on return type?

No. Overloading is a term that is strongly related to the method signature definition. The method signature includes:

  • the method name
  • the method parameters

Overloading specifies two or more methods with the name, but different method signature. The return-type is not part of the method signature.

In your example, the three method definitions are not overloaded, but overridden versions of one and the same method abstraction.

Upvotes: 1

TheLostMind
TheLostMind

Reputation: 36304

From javadocs we have :

Returns an array containing Method objects reflecting all the public member methods of the class or interface represented by this Class object, including those declared by the class or interface and those inherited from superclasses and superinterfaces. Array classes return all the (public) member methods inherited from the Object class. The elements in the array returned are not sorted and are not in any particular order. This method returns an array of length 0 if this Class object represents a class or interface that has no public member methods, or if this Class object represents a primitive type or void.

 StringBuilder extends AbstractStringBuilder 

 AbstractStringBuilder implements Appendable

That's why you get 3 methods.

Upvotes: 1

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