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javaarrays
DivideByHero
DivideByHero

Reputation: 20355

Any way to declare an array in-line?

Let's say I have a method m() that takes an array of strings as an argument. Is there a way I can just declare this array in-line when I make the call, i.e. instead of

String[] strs = {"blah", "hey", "yo"};
m(strs);

Can I just replace this with one line, and avoid declaring a named variable that I'm never going to use?

Upvotes: 735

Views: 473758

Answers (8)

Gibolt
Gibolt

Reputation: 47287

You can directly write the array in modern Java, without an initializer. Your example is now valid. It is generally best to name the parameter anyway.

String[] array = {"blah", "hey", "yo"};

or

int[] array = {1, 2, 3};

If you have to inline, you'll need to declare the type:

functionCall(new String[]{"blah", "hey", "yo"});

or use varargs (variable arguments)

void functionCall(String...stringArray) {
    // Becomes a String[] containing any number of items or empty
}

functionCall("blah", "hey", "yo");

Hopefully Java's developers will allow implicit initialization in the future

Update: Kotlin Answer

Kotlin has made working with arrays so much easier! For most types, just use arrayOf and it will implicitly determine type. Pass nothing to leave them empty.

arrayOf("1", "2", "3") // String
arrayOf(1, 2, 3)       // Int
arrayOf(1, 2, "foo")   // Any 
arrayOf<Int>(1, 2, 3)  // Set explict type
arrayOf<String>()      // Empty String array

Primitives have utility functions. Pass nothing to leave them empty.

intArrayOf(1, 2, 3)
charArrayOf()
booleanArrayOf()
longArrayOf()
shortArrayOf()
byteArrayOf()

If you already have a Collection and wish to convert it to an array inline, simply use:

collection.toTypedArray()

If you need to coerce an array type, use:

array.toIntArray()
array.toLongArray()
array.toCharArray()
...

Upvotes: 38

Shravan Ramamurthy
Shravan Ramamurthy

Reputation: 4096

Other option is to use ArrayUtils.toArray in org.apache.commons.lang3

ArrayUtils.toArray("elem1","elem2")

Upvotes: 8

Mahpooya
Mahpooya

Reputation: 559

You can create a method somewhere

public static <T> T[] toArray(T... ts) {
    return ts;
}

then use it

m(toArray("blah", "hey", "yo"));

for better look.

Upvotes: 13

Jonathan Weatherhead
Jonathan Weatherhead

Reputation: 1580

As Draemon says, the closest that Java comes to inline arrays is new String[]{"blah", "hey", "yo"} however there is a neat trick that allows you to do something like

array("blah", "hey", "yo") with the type automatically inferred.

I have been working on a useful API for augmenting the Java language to allow for inline arrays and collection types. For more details google project Espresso4J or check it out here

Upvotes: 0

Michael Myers
Michael Myers

Reputation: 192025

Draemon is correct. You can also declare m as taking varargs:

void m(String... strs) {
    // strs is seen as a normal String[] inside the method
}

m("blah", "hey", "yo"); // no [] or {} needed; each string is a separate arg here

Upvotes: 132

Antonio Carlos
Antonio Carlos

Reputation: 780

Another way to do that, if you want the result as a List inline, you can do it like this:

Arrays.asList(new String[] { "String1", "string2" });

Upvotes: 31

Bill K
Bill K

Reputation: 62789

I'd like to add that the array initialization syntax is very succinct and flexible. I use it a LOT to extract data from my code and place it somewhere more usable.

As an example, I've often created menus like this:

Menu menu=initMenus(menuHandler, new String[]{"File", "+Save", "+Load", "Edit", "+Copy", ...});

This would allow me to write come code to set up a menu system. The "+" is enough to tell it to place that item under the previous item.

I could bind it to the menuHandler class either by a method naming convention by naming my methods something like "menuFile, menuFileSave, menuFileLoad, ..." and binding them reflectively (there are other alternatives).

This syntax allows AMAZINGLY brief menu definition and an extremely reusable "initMenus" method. (Yet I don't bother reusing it because it's always fun to write and only takes a few minutes+a few lines of code).

any time you see a pattern in your code, see if you can replace it with something like this, and always remember how succinct the array initialization syntax is!.

Upvotes: 4

Draemon
Draemon

Reputation: 34721

m(new String[]{"blah", "hey", "yo"});

Upvotes: 1115

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