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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