Question

Why does return type of method not included in signature?

An example

public void method1(String arg){...}

public String method1(String arg){...}

It will cause an error.

Answer 1

This is done because the compiler would not be able to figure out the overload in all contexts.

For example, if you call

String x = method1("aaa");

the compiler knows that you are looking for the second overload. However, if you call

method1("aaa");

like this, the compiler has no idea which one of the two methods you wanted to invoke, because it is OK to call a method returning String and discard the result. To avoid ambiguities like this, Java prohibits overloads that differ solely on the return type.