在下面代码中System.out.println的输出结果是什么？import java.util.*;public class Main {public static void main(String args[]) {Stack mystack1=new Stack(),mystack2=new Stack();StringBuffer bu=new StringBuffer();for(char c='A';c<='D';c++) {mystack1.push(new Character(c)); }while(!(mystack1.empty())) {Character temp=mystack1.pop();mystack2.push(temp);}while(!(mystack2.empty())) {Character temp=mystack2.pop();bu.append(temp.charValue());}System.out.println(bu);}}