case "D":
System.out.print("确认是否退出(Y/N):");
String isExit=scan.next();
if(isExit=="Y" || isExit=="y"){
isFlag=false;
}else if(isExit=="N" || isExit=="na"){
isFlag=true;
}else{
System.out.println("请输入正确的选项!");
}
break;
default:
System.out.println("请选择A--D!");
}