用java或者c/c++如何将“明天”“一周内” “未来三天“这种词转化为当时的时间呢？这个函数应该如何写，流程思想是什么？请大侠赐教!

public class TestCalendar {
    public static void main(String[] args) {
        tc.method3("今天");
        tc.method3("明天");
        tc.method3("未来三天");
    }
    
    private void method3(String str){
        char c = ' ';
        if(str.equals("今天")){
            c = 'T';
        }else if(str.equals("明天")){
            c = 'O';
        }else if(str.equals("未来三天")){
            c = 'F';
        }
        Calendar cal = Calendar.getInstance();
        int day = cal.get(DATE);
        int month = cal.get(MONTH);
        switch (c) {
        case 'T':
            System.out.println(cal.get(MONTH)+"月"+cal.get(DATE)+"日");
            break;
        case 'O':
            cal.add(DATE, 1);
            System.out.println(cal.get(MONTH)+"月"+cal.get(DATE)+"日");
            break;
        case 'F':
            System.out.print(cal.get(MONTH)+"月"+cal.get(DATE)+"日到");
            cal.add(DATE, 3);
            System.out.println(cal.get(MONTH)+"月"+cal.get(DATE)+"日");
            break;
        default:
            break;
        }
    }
}