Passing arrays as method parameters in Java

Question

The following code uses simple arrays of String in Java.

package javaarray;

final public class Main
{
    public void someMethod(String[] str)
    {
        System.out.println(str[0]+"\t"+str[1]);
    }
    public static void main(String[] args)
    {
        String[] str1 = new String[] {"day", "night"};
        String[] str2 = {"black", "white"};

        //Both of the above statements are valid.

        Main main=new Main();
        main.someMethod(str1);
        main.someMethod(str2);

        //We can invoke the method someMethod by supplying both of the above arrays alternatively.

        main.someMethod(new String[] { "day", "night" }); //This is also valid as obvious.
        main.someMethod({ "black", "white" }); //This is however wrong. The compiler complains "Illegal start of expression not a statement" Why?
    }
}

In the above code snippet, we can initialize arrays like this.

String[] str1 = new String[] {"day", "night"};
String[] str2 = {"black", "white"};

and we can directly pass it to a method without being assigned like this.

main.someMethod(new String[] { "day", "night" });

If it is so, then the following statement should also be valid.

main.someMethod({ "black", "white" });

but the compiler complains "Illegal start of expression not a statement" Why?

I guess you somehow need to pass the reference of the string array. By what you are doing, that does not happen. — noMAD
– noMAD, Commented Apr 12, 2012 at 3:47
It might be hard to parse properly in the form you want, for example if the compiler sees {1, 12, 57}, what should it be -- a byte[], short[], int[], or long[]? With the explicit type, the ambiguity is gone. — trutheality
– trutheality, Commented Apr 12, 2012 at 3:59

default locale · Accepted Answer · 2018-01-08 05:00:05Z

8

According to Java Language Specification (10.6. Array Initializers)

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:

So, there are only two ways you can use an array initializer ({"foo", "bar"}):

Variable declaration: String[] foo = {"foo", "bar"};
Array creation expression: new String[] {"foo", "bar"};

You can't use an array initializer as a method parameter.

15.10. Array Creation Expressions

ArrayCreationExpression:
    new PrimitiveType DimExprs Dimsopt
    new ClassOrInterfaceType DimExprs Dimsopt
    new PrimitiveType Dims ArrayInitializer 
    new ClassOrInterfaceType Dims ArrayInitializer

edited Jan 8, 2018 at 5:00

answered Apr 12, 2012 at 3:48

default locale

13.6k13 gold badges60 silver badges68 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

user unknown Over a year ago

You don't mean can't use it only ..., do you?

noMAD Over a year ago

In this sentence So, you can use it only as a part of array creation expression can I know you are referring to it as?

default locale Over a year ago

@noMAD, it is an array initializer. I'll try to improve my answer, though.

Lion Over a year ago

Please include the JLS link so that it may also be more helpful to future visitors.

Collectives™ on Stack Overflow

Passing arrays as method parameters in Java

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related