Java array initialization within argument list

Question

How come the first call to someMethod doesn't compile without being explicit that it's String[]?

It's fine to use an array initializer to create a String[] array but you can't use it to pass an argument. Are the curly braces used in some other fashion for passing arguments that derails how I'd expect this to behave?

public void someMethod(String[] arr){
    //do some magic
}

public void makeSomeMagic(){

    String[] arr = {"cat", "fish", "cow"};

    //Does not compile!
    someMethod({"cat", "fish", "cow"});

    //This compiles!
    someMethod(new String[]{"cat", "fish", "cow"});

    //This compiles!
    someMethod(arr);
}

The compiler error is the following:

The method someMethod(String[]) in the type Moo is not applicable for the arguments (String, String, String)

Its only allowed at declaration time. It's a syntax thing

Matt Phillips
– Matt Phillips

2010-12-14 20:31:51 +00:00
Commented Dec 14, 2010 at 20:31 — Matt Phillips
– Matt Phillips, Commented Dec 14, 2010 at 20:31

aioobe · Accepted Answer · 2010-12-14 20:42:24Z

14

You can only use the { "hello", "world" } initialization notation when declaring an array variable or in an array creation expression such as new String[] { ... }.

See Section 10.6 Array Initializers in the Java Language Specification:

An array initializer may be specified in a declaration, or as part of an array creation expression (§15.10), creating an array and providing some initial values

edited Dec 14, 2010 at 20:42

answered Dec 14, 2010 at 20:30

aioobe

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Comments

MiKo · Accepted Answer · 2010-12-14 20:40:15Z

5

If you don't want to use explicit String[], use:

public void someMethod(String... arr){
    //do some magic
}
…
someMethod("cm", "applicant", "lead");

The three periods after the final parameter's type indicate that the final argument may be passed as an array or as a sequence of arguments.

2 Comments

aioobe Over a year ago

That will only work if he changes the signature to String... args.

Nick Swarr Over a year ago

Perfect, this gives me exactly what I was looking for. Thanks!

Goran Jovic · Accepted Answer · 2010-12-14 20:35:26Z

1

Or you can use varargs:

public void someMethod(String... arr){
    //do some magic
}

public void makeSomeMagic(){
    someMethod("cat", "fish", "cow");
}

It's basically a fancy syntax for an array parameter (vararg must be the last parameter in method signature).

answered Dec 14, 2010 at 20:35

Goran Jovic

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Comments

Ralph · Accepted Answer · 2010-12-14 20:35:57Z

0

You can use the curly braces to initialize an array. In every else case it is used to define blocks of statments.

answered Dec 14, 2010 at 20:35

Ralph

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