Yes, that is how it works. The arguments are automatically put into an array. The argument "urls" behaves like a URL[]. Varargs are documented here. They were introduced in Java 1.5, so, are available in J2SE 1.5+, and all of Android since it supports Java 1.5+ language features. No version of JavaME/J2ME supports it.
In Effective Java, Chapter 7 (Methods), Item 40 (Design method signatures carefully), Bloch writes:
There are three techniques for shortening overly long parameter lists:
- break the method into multiple methods, each which require only a subset of the parameters
- create helper classes to hold group of parameters (typically static member classes)
- adapt the Builder pattern from object construction to method invocation.
For more details, I encourage you to buy the book, it's really worth it.
Using a map with magical String keys is a bad idea. You lose any compile time checking, and it's really unclear what the required parameters are. You'd need to write very complete documentation to make up for it. Will you remember in a few weeks what those Strings are without looking at the code? What if you made a typo? Use the wrong type? You won't find out until you run the code.
Instead use a model. Make a class which will be a container for all those parameters. That way you keep the type safety of Java. You can also pass that object around to other methods, put it in collections, etc.
Of course if the set of parameters isn't used elsewhere or passed around, a dedicated model may be overkill. There's a balance to be struck, so use common sense.
The solution depends on the answer to the question - are all the parameters going to be the same type and if so will each be treated the same?
If the parameters are not the same type or more importantly are not going to be treated the same then you should use method overloading:
public class MyClass
{
public void doSomething(int i)
{
...
}
public void doSomething(int i, String s)
{
...
}
public void doSomething(int i, String s, boolean b)
{
...
}
}
If however each parameter is the same type and will be treated in the same way then you can use the variable args feature in Java:
public MyClass
{
public void doSomething(int... integers)
{
for (int i : integers)
{
...
}
}
}
Obviously when using variable args you can access each arg by its index but I would advise against this as in most cases it hints at a problem in your design. Likewise, if you find yourself doing type checks as you iterate over the arguments then your design needs a review.
Suppose you have void method that prints many objects;
public static void print( Object... values){
for(Object c : values){
System.out.println(c);
}
}
Above example I used vararge as an argument that accepts values from 0 to N.
From comments: What if 2 strings and 5 integers ??
Answer:
print("string1","string2",1,2,3,4,5);
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)
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);