string.split(",");

------解决方案--------------------
Java code

public class Test
{
    public static void main(String[] args) 
    {
        String str = "B1,B2,B3,B4,B5";
        Object[] o = str.split(",");
        for(int i = 0;i < o.length;i++)
        {
            System.out.println(o[i]);
        }
    }
}

------解决方案--------------------
String[] a="B1,B2,B3,B4,B5".split(",")