pengliangaiqiqi的博客

public static void main(String[] args) { int[] a = {1,2,3,4,5,6,7,8}; int[] b = new int[10]; System.arraycopy(a, 1, b, 3, 3); //结果： a :[1,2,3,4,5,6,7,8] b :[0,0,0,2,3,4,0,0,0,0] ...

1.查看当前日期时间并输出 Calendar cal = Calendar.getInstance(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd hh:mm:ss"); System.out.println(sdf.format(cal.getTime())); System.out.println("------

1.String JVM不断地创建新对象，并回收老对象 String str = "abc"; str += "de";  //创建了两个对象 String str = "abc" + "de";  //创建了一个对象 2.单就速度而言，速度比较：StringBuilder > StringBuffer > String 3.StringBuilder 是线程不安全的，StringBuff