How can I create a Java method that accepts a variable number of arguments?

Question

For example, Java's own String.format() supports a variable number of arguments.

String.format("Hello %s! ABC %d!", "World", 123); //=> Hello World! ABC 123! 

How can I make my own function that accepts a variable number of arguments?

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Follow-up question:

I'm really trying to make a convenience shortcut for this:

System.out.println( String.format("...", a, b, c) ); 

So that I can call it as something less verbose like this:

print("...", a, b, c); 

How can I achieve this?

Answer 1

You could write a convenience method:

public PrintStream print(String format, Object... arguments) {     return System.out.format(format, arguments); } 

But as you can see, you've simply just renamed format (or printf).

Here's how you could use it:

private void printScores(Player... players) {     for (int i = 0; i < players.length; ++i) {         Player player = players[i];         String name   = player.getName();         int    score  = player.getScore();         // Print name and score followed by a newline         System.out.format("%s: %d%n", name, score);     } }  // Print a single player, 3 players, and all players printScores(player1); System.out.println(); printScores(player2, player3, player4); System.out.println(); printScores(playersArray);  // Output Abe: 11  Bob: 22 Cal: 33 Dan: 44  Abe: 11 Bob: 22 Cal: 33 Dan: 44 

Note there's also the similar System.out.printf method that behaves the same way, but if you peek at the implementation, printf just calls format, so you might as well use format directly.

• Varargs
• PrintStream#format(String format, Object... args)
• PrintStream#printf(String format, Object... args)

Answer 2

This is known as varargs see the link here for more details

In past java releases, a method that took an arbitrary number of values required you to create an array and put the values into the array prior to invoking the method. For example, here is how one used the MessageFormat class to format a message:

Object[] arguments = {     new Integer(7),     new Date(),     "a disturbance in the Force" };     String result = MessageFormat.format(         "At {1,time} on {1,date}, there was {2} on planet "          + "{0,number,integer}.", arguments); 

It is still true that multiple arguments must be passed in an array, but the varargs feature automates and hides the process. Furthermore, it is upward compatible with preexisting APIs. So, for example, the MessageFormat.format method now has this declaration:

public static String format(String pattern,                             Object... arguments);