Question

I’m trying to build a litle gam for android GSMs. I hava lots of units and all of them have destinations. To calculate destination I’m using a function called CalDes. This function CalDes is calculating my unit’s speed. So I’m sending some variables into which I have to edit and use em again. For this I have to send these variables with reference. Here is a simple for C++ How to do that in java?

void swap(SomeType& arg1, Sometype& arg2) {
    SomeType temp = arg1;
    arg1 = arg2;
    arg2 = temp;
}
...
SomeType var1 = ...; // value "A"
SomeType var2 = ...; // value "B"
swap(var1, var2); // swaps their values!

Answer 1

Java doesn’t have pass-by-reference at all. You have a couple of options:

1. Pass the data in an array:

   void swap(SomeType[] args) {
       SomeType temp = args[0];
       args[0] = args[1];
       args[1] = temp;
   }
   

   …but using it is a pain in the calling code:

   SomeType a = ...;
   SomeType b = ...;
   SomeType[] args = new SomeType[] { a, b };
   swap(args);
   a = args[0];
   b = args[1];
   

2. Create an object that has public SomeType members, and pass in the object reference.

   void swap(SomeTypeContainer c) {
       SomeType temp = c.a;
       c.a = c.b;
       c.b = temp;
   }
   

   Which is very similar to #1, but probably more convenient to work with from calling code.

   SomeTypeContainer c = new SomeTypeContainer(/* ... something that creates a and b ... */);
   // Use c.a and c.b directly
   swap(c);
   // Use c.a and c.b directly, they're now swapped