java中string和stringbuffer的区别

package om.yuanguang;
public class TestString {
public static void main(String[] args) {
StringBuffer s0 = new StringBuffer("A");
StringBuffer s1 = new StringBuffer("B");

    comp(s0,s1);
    System.out.println(s0+"---"+s1);
}

public static void comp(StringBuffer s0,StringBuffer s1){
    s0.append(s1);
    s1 = s0;
}

}

求结果及具体的分析过程、原理