java - Why varargs should be the last in method signature?

Question

If I try to write a method like below

public void someStuff(Object ... args, String a )

I get this error

The variable argument type Object of the method someStuff must be the last parameter.

I don't fully understand the requirement of variable argument type to be the last. Any inputs will be helpful.

Answer 1

The variable argument has to be the last so the compiler can work out which argument is which.

For example, say you pass

"test", "test", "test", "test"

into your function

public void someStuff(Object ... args, String a)

Java cannot work out if you want the args variable to contain 3 or 4 strings. It may be obvious to you at the time of writing but it's ambiguous.

However, when it's the other way around

public void someStuff(String a, Object ... args)

The Java compiler sees the first string, stick it into "a" and then knows that the remaining strings can be safely put into args and there is no ambiguity over the variables.