Understanding the bitwise OR of SWT Constants

Question

I'm examining some SWT code and I'm having trouble understanding how the SWT constants work and particularly, how their bitwose OR works.

For example:

final Table leftTable = new Table(parent, SWT.MULTI | SWT.FULL_SELECTION);

I looked up SWT.MULTI in the API and found that its value is 1<<1. What does this mean? I did the same for SWT.FULL_SELECTION and found its value to be 13 (more understandable).

What does it mean to bitwise OR these? Is there a quick way to determine what the result is? Why is it done this way?

Answer 1

There is a complete list of the style bits here and an excellent explanation here and a general explanation on bitwise operators here.

<< is the left bit shift operator as explained here.

---

Let's make an example:

Assuming you have two style bits:

SWT.FOO = 4  // 100 binary
SWT.BAZ = 2  // 010 binary

If you now give SWT.FOO | SWT.BAZ to the Table, the result will be:

   100
OR 010
   ---
   110 // 6 in decimal

The table now wants to find out if you selected SWT.BAZ. It can do so by checking the following:

int styleBit = 6; // 110 binary

if((styleBit & SWT.BAZ) == SWT.BAZ)
{
    System.out.println("SWT.BAZ selected");
}

You can verify this calculation here.