Item 42 - Use varargs judiciously
From Effective Java 2/e by Joshua Bloch
Varargs stands for variable arity method
Simple use of varargs
static int sum(int... args) {
int sum = 0;
for (int arg : args)
sum += arg;
return sum;
}
Use varargs to pass one or more arguments
static int min(int firstArg, int... remainingArgs) {
int min = firstArg;
for (int arg : remainingArgs)
if (arg < min)
min = arg;
return min;
}
- Don’t retrofit every method that has a final array parameter; use varargs only when a call really operates on a variable-length sequence of values.
// Consider the case of Arrays.asList
// This method was never designed to gather multiple arguments into a list
// but it seemed like a good idea to retrofit it to do so when varargs were added to the platform
// As a result, it became possible to do things like this
List<String> homophones = Arrays.asList("to", "too", "two");
// Obsolete idiom to print an array!
// It prints [Ljava.lang.Integer;@3e25a5.
System.out.println(Arrays.asList(myArray));
// The right way to print an array
System.out.println(Arrays.toString(myArray));
// If you accidentally tried it on an array of primitives, the program wouldn’t compile
// Error: asList(Object[]) in Arrays can't be applied to (int[])
public static void main(String[] args) {
int[] digits = { 3, 1, 4, 1, 5, 9, 2, 6, 5, 4 };
System.out.println(Arrays.asList(digits));
}
- Exercise care when using the varargs facility in performance-critical situations. Every invocation of a varargs method causes an array allocation and initialization.
