illegal start of expression -- arrays

[Kai Middleton]

Why is the java language structured such that in regard to my second invocation of the foo method I get a compiler error:

public class IllegalStartOfExpression
{
public static void main(String [] args)
{
int[] x = {1, 2};
foo(x);
// the following line causes a compiler error of
// "illegal start of expression"
foo({1, 2});
}
public static void foo(int[] x)
{
System.out.println(x[0]);
}
}

[Anonymous]

The problem is that your foo method requires an int array and that is not what you are passing it. Arrays in java are objects, so you need to create one to send. It looks to me like neither invocation will work. All objects, except Strings, need to be explicitly created with the new keyword.
public class IllegalStartOfExpression{
public static void main(String [] args){
int[] x = new int[]{1, 2};
foo(x);
foo(new int[]{1, 2});
}
public static void foo(int[] x){
System.out.println(x[0]);
}
}

------------------
Brian Hoff
Sun Certified Programmer for the Java� 2 Platform

[Mike Curwen]

If I could add something: The confusing thing about anonymous arrays (which is what we're talking about), is that at first glance it appears that an initialization list is the anonymous array:

public class AnonArray {
public static void main(String args[]) {
int[] array1 = {1};
        // array1 is declared and initialized in one step
int[] array2 = new int[] {1,2};
        // array2 is declared and the anonymous array made 
        // on the right hand side is assigned to array2 
forSakeOfArgument(array1);
forSakeOfArgument(array2);
forSakeOfArgument(new int[] {1,2,3});
        // an anonymous array is passed to the function
//forSakeOfArgument({1,2,3,4});
        // there is NOT enough information here for the 
        // compiler to determine the {} contains integers
        // (uncomment the line, and you get compile error)
}
private static void forSakeOfArgument(int[] arg) {
System.out.println("passed array: " + arg.length);
}
}
//  OUTPUT   //
passed array: 1
passed array: 2
passed array: 3

The confusing part (for me) was that I have a book that says The construct (ie: the anonymous array) returns an array reference which can be assigned, and passed as a parameter. In particular, the following two examples are equivalent:
int[] intArray = {2,3,4,5};
int[] intArray = new int[] {2,3,4,5};

I thought that {2,3,4,5} was an anonymous array, but of course it's not, it's simply an initialization list, and not the anonymous array itself. So this list by itself cannot be passed to a method which expects an array.