How to call a varargs method with an additional argument from a varargs method

问题

I have some varargs system function, where T is some actual type, like String:

sys(T... args)

I want to create own function, which delegates to the system function. My function is also a varargs function. I want to pass through all the arguments for my function through to the system function, plus an additional trailing argument. Something like this:

myfunc(T... args) {
    T myobj = new T();
    sys(args, myobj); // <- of course, here error.
}

How do I need to change the line with the error? Now I see only one way: create array with dimension [args] + 1 and copy all items to the new array. But maybe there exists a more simple way?

回答1:

Now I see only one way: create array with dimension [args] + 1 and copy all items to new array.

There is no simpler way. You need to create a new array and include myobj as last element of the array.

String[] args2 = Arrays.copyOf(args, args.length + 1);
args2[args2.length-1] = myobj;
sys(args2);

If you happen to depend on Apache Commons Lang you can do

sys(ArrayUtils.add(args, myobj));

or Guava

sys(ObjectArrays.concat(args, myobj));

回答2:

You may call sys() twice if the order doesn't care:

T myobj=new T();
sys(myobj);
sys(args);

If you can't use this, switch to collections (eg. LinkedList) for all of your functions.

回答3:

If you can use Guava, then you can do:

sys(ObjectArrays.concat(myobj, args))

回答4:

Java 8 solution:

sys(Stream.concat(Arrays.stream(args), Stream.of(myobj)).toArray(T[]::new));

来源：https://stackoverflow.com/questions/27293989/how-to-call-a-varargs-method-with-an-additional-argument-from-a-varargs-method