CODEWITHSUNDEEP
javaoverloadingoverriding
Sumit Surana
Sumit Surana

Reputation: 1584

The method is ambigous - Java

I was trying to some examples and was not able to understand the reason for following code error in the following example

public class Test {
public static void print(Integer object){
    System.out.println("object");
}
public static void print(String string){
    System.out.println("String");
}
public static void main(String... args){
    print(null);
}
}

I am getting error as: The method print(Integer) is ambiguous for the type Test

but when I am trying the same example by changing Integer to Object the code compiles fine and gives output as String

public class Test {
public static void print(Object object){
    System.out.println("object");
}
public static void print(String string){
    System.out.println("String");
}
public static void main(String... args){
    print(null);
}
}

Can anyone please help me in understanding why the method with Object in its signature is required when the output is from the method which is having String in it. And what is the reason for the ambiguous type error.

Upvotes: 2

Views: 1203

Answers (3)

Jeff-Inventor ChromeOS
Jeff-Inventor ChromeOS

Reputation: 295

A common practice to disambiguate methods such as this is adding type information into the method name. This has the advantage of making the code explicit and clear, rather than using function overloading to resolve which method is called.

public class Test {
public static void printInteger(Integer object){
    System.out.println("object");
}
public static void printString(String string){
    System.out.println("String");
}
public static void main(String... args){
    printInteger(null);
}
}

Upvotes: 2

Braj
Braj

Reputation: 46841

Integer and String are not in same hierarchies. It means you can't assign String into Integer and vice-verse.

but it's not case with Stringand Object because in java every class extends Object class by default.

The Java Language Specification (JLS) in section 15.12 Method Invocation Expressions explains in detail the process that the compiler follows to choose the right method to invoke.

There, you will notice that this is a compile-time task. The JLS says in subsection 15.12.2:

This step uses the name of the method and the types of the argument expressions to locate methods that are both accessible and applicable There may be more than one such method, in which case the most specific one is chosen.

Read more about Java overloading rules

See Method overloading and choosing the most specific type

Look at below sample code where Integer and Number are in same hierarchy that why it's valid. 

class Test {
    public  void print(Integer object) {
        System.out.println("object");
    }

    public  void print(Number string) {
        System.out.println("String");
    }
}
new Test().print(null);

enter image description here

Upvotes: 3

Zoltán
Zoltán

Reputation: 22156

Null doesn't have a type in Java. When you call print(null), the compiler doesn't know whether you want to call the print(String) function or the print (Integer) function.

The solution is to explicitly cast into the type you want called

print((Integer)null);

or

print((String)null);

Upvotes: 3

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