Remove Assignments to Parameters

@Test
    public void DateTest() {
        Date currentdate = new Date();
        System.out.println("before is " + currentdate);
        nextDate(currentdate);
        System.out.println("after is " + currentdate);
    }

/**
 * 不要对 方法传递过来的对象进行赋值 , 如果想要修改对象 , 请使用return
 * @param currentdate
 */
public void nextDate(Date currentdate) {
    Date date = new Date();//取时间
    Calendar calendar = new GregorianCalendar();
    calendar.setTime(date);
    calendar.add(Calendar.DATE, -1);//把日期往前减少一天，若想把日期向后推一天则将负数改为正数
    date = calendar.getTime();
    currentdate=date;
    System.out.println(currentdate);
}

before is Thu Aug 10 11:18:46 CST 2017
Wed Aug 09 11:18:46 CST 2017
after is Thu Aug 10 11:18:46 CST 2017