如何优化Java按月份列生日名单代码并显示无生日的月份

算力阿峰

2026-10-6

实现方案

核心思路

预先定义月份名称映射表，用数组下标对应月份，消除冗余if分支
先将所有员工按生日月份分组存储，再按1-12月的固定顺序遍历输出，确保空月份也能正常显示

实现代码

private Employee[] arr = new Employee[8];//Employee类
// 预定义完整月份名称，下标0对应1月，下标1对应2月，以此类推
private static final String[] MONTH_NAMES = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};

public String birthdays() throws ParseException{
    StringBuilder list = new StringBuilder();
    // 初始化12个月份对应的员工列表
    List<String>[] monthBirthList = new List[12];
    for (int i = 0; i < 12; i++) {
        monthBirthList[i] = new ArrayList<>();
    }

    // 遍历所有员工，按月份分组
    for (Employee employee : arr) {
        // 截取月份字符串转成数字，转成数组下标要减1
        int month = Integer.parseInt(employee.getDob().substring(3, 5)) - 1;
        monthBirthList[month].add(employee.getName() + " " + employee.getSurname());
    }

    // 按顺序输出12个月份的内容
    for (int i = 0; i < 12; i++) {
        list.append(MONTH_NAMES[i]).append(":\n");
        if (monthBirthList[i].isEmpty()) {
            list.append("//no birthday in ").append(MONTH_NAMES[i]).append("\n");
        } else {
            for (String name : monthBirthList[i]) {
                list.append(name).append("\n");
            }
        }
        // 月份之间加空行分隔，和示例格式一致
        list.append("\n");
    }

    // 如需直接打印输出可新增System.out.println(list)语句
    return list.toString().trim(); // trim去掉末尾多余空行
}