Can Java Methods with Variable Arguments Accept an Array as Multiple Arguments?
Can Arguments Be Passed as an Array to a Method with Variable Arguments in Java?
Consider the following desired function:
class A { private String extraVar; public String myFormat(String format, Object ... args) { return String.format(format, extraVar, args); } }
In this scenario, args is interpreted as Object[] within the myFormat method, resulting in a single argument being provided to String.format. However, the aim is to have each Object in args passed as a distinct argument.
Is It Possible?
Yes, it is possible since T... is merely syntactic sugar for T[].
Java Language Specification (JLS) 8.4.1 defines:
The last formal parameter in a list is special; it may be a variable arity parameter, indicated by an elipsis following the type.
If the last formal parameter is a variable arity parameter of type T, it is considered to define a formal parameter of type T[].
Example Illustrating Variable Arity Parameter:
public static String ezFormat(Object... args) { String format = new String(new char[args.length]) .replace("<pre class="brush:php;toolbar:false">static void count(Object... objs) { System.out.println(objs.length); } count(null, null, null); // prints "3" count(null, null); // prints "2" count(null); // throws NullPointerException!!!", "[ %s ]"); return String.format(format, args); } public static void main(String... args) { System.out.println(ezFormat("A", "B", "C")); // prints "[ A ][ B ][ C ]" }
In the main method, args is a String[], which is passed to ezFormat. The method treats it as Object[] because of covariance.
Varargs Gotchas:
Passing null
int[] myNumbers = { 1, 2, 3 }; System.out.println(ezFormat(myNumbers)); // prints "[ [I@13c5982 ]"
To work around this, call with Object[] { null } or (Object) null.
Adding Extra Arguments to an Array
To pass an array of primitive types, wrap it in a reference array:
Integer[] myNumbers = { 1, 2, 3 }; System.out.println(ezFormat(myNumbers)); // prints "[ 1 ][ 2 ][ 3 ]"
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