Varargs
Java has a feature where we can define a method to take a variable number of arguments.
- We call this feature varargs and recognize it by the
...in a method's parameter list.
public static void varArgsMethod(String... stringArr){
// ...
}
We can pass this method zero or more String arguments, separated by commas.
varArgsMethod();
varArgsMethod("Mick", "Keith");
Java takes these zero or more String arguments and puts them into an array.
- We can access the
Strings by their array index.
public static void varArgsMethod(String... stringArr){
for (int i = 0; i < stringArr.length; i++) {
System.out.println(stringArr[i]);
}
}
Practice Exercise¶
A varargs array parameter is never null - just like main's args, you can safely access its length or iterate over its elements.
It is important to check the length of the array or use a foreach loop, because the array could be zero-length.
Varargs Is Always the Last Parameter¶
A varargs parameter must always be the last parameter in a method's parameter list.
Therefore, there cannot be more than one varargs parameter in a parameter list.
// YES
public void varArgsMethod(int x, int y, String...stringArgs) {
// ...
}
//NO - WILL NOT COMPILE, VARARGS MUST BE LAST
public void badVarArgsMethodFirst(String...stringArgs, int x) {
// ...
}
//NO - WILL NOT COMPILE, VARARGS MUST BE LAST, intArgs IS NOT LAST
public void badVarArgsMethod(int...intArgs, String... stringArgs) {
// ...
}
Practice Exercise¶
A main method defined with varargs is legal, and the java command will be able to run a program with this main signature.
public static void main(String... args){
// ...
}
Drill¶
AdvancedArrays/com.example.advancedarrays.drills.VarArgsBand
* Run the program, passing a band name and list of members. Is the output what you expected?
* Can you call the method with zero arguments? Why or why not?