How to Resolve Method Overloading Ambiguity with Null Arguments in Java?

Method Overloading with Null Argument: Resolving Ambiguity

In Java, method overloading allows multiple methods with the same name but different parameter types. However, passing a null argument to overloaded methods can lead to compiler errors. Let's explore the issue and its solution.

Consider the following code snippet:

public static void doSomething(Object obj) {
    System.out.println("Object called");
}

public static void doSomething(char[] obj) {
    System.out.println("Array called");
}

public static void doSomething(Integer obj) {
    System.out.println("Integer called");
}

Invoking doSomething(null) results in a compilation error due to method ambiguity. Java cannot determine which version of doSomething to call since Integer, char[], and Object can all accept null values.

The issue lies with the equally specific nature of the Integer and char[] methods. Both are more specific than the Object method because they define a narrower parameter type. Therefore, Java cannot prioritize one method over the other.

To resolve this ambiguity, you must explicitly specify the intended method by casting the argument to the desired type. For instance:

doSomething((Object) null); // Calls doSomething(Object obj)
doSomething((char[]) null); // Calls doSomething(char[] obj)

Alternatively, you can make the parameter type non-nullable in one of the overloaded methods. This would ensure that null cannot be passed as an argument to that version. For example:

public static void doSomething(Object obj) {
    System.out.println("Object called");
}

public static void doSomething(char[] obj) { // Parameter type not nullable
    System.out.println("Array called");
}

By casting the argument or making the parameter type non-nullable, you provide Java with additional information to disambiguate the method call.

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