Concatenate variable argument list

Question

I want to prepend a String to a variable list of String arguments.

public String myMethod(String... args) {
    return myOtherMethod("some string" + args);
}

Now, this of course will not work, because you cannot add these two types as such. How can I insert this string at the beginning of the list and then call myOtherMethod()?

EDIT: myOtherMethod() takes another String... as its argument. I am also limited to Java 7.

What is the type of myOtherMethod? Does it accept another String...? Just one String? — Louis Wasserman
– Louis Wasserman, Commented Jun 18, 2015 at 20:21
So you only need to create a new array with "some string" as the first element, right? — Luiggi Mendoza
– Luiggi Mendoza, Commented Jun 18, 2015 at 20:29
do you want to return the big concatenated string from myOtherMethod? — Blake Yarbrough
– Blake Yarbrough, Commented Jun 18, 2015 at 20:30

Louis Wasserman · Accepted Answer · 2015-06-18 20:30:06Z

3

There isn't a way around creating a new String[], like so:

public String myMethod(String... args) {
  String[] concatenatedArray = new String[args.length + 1];
  concatenatedArray[0] = "other string";
  for (int i = 0; i < args.length; i++) { // or System.arraycopy...
    concatenatedArray[i + 1] = args[i];
  }
  return myOtherMethod(concatenatedArray);
}

Or, if third-party libraries are allowed, using Guava you could just write

return myOtherMethod(ObjectArrays.concat("other string", args));

answered Jun 18, 2015 at 20:30

Louis Wasserman

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2 Comments

Luiggi Mendoza Over a year ago

You can also use System.arraycopy(args, 0, concatenatedArray, 1, concatenatedArray.length - 1); rather than use the for.

Louis Wasserman Over a year ago

Yep. (As I alluded to in the comment.)

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