小技巧

隐藏手机号码

if(ss.startsWith("86")) {
	ss = ss.substring(0, 5)+"****"+ss.substring(9, 13);
}else {
	ss = ss.substring(0, 3)+"****"+ss.substring(7, 11);
}

二分递归

public static int ab(int[] i, int a, int b) { // a=0 b=leng-1/2
        if (a + 1 == b)
            return b + 1;
        if (i[(a + b) / 2] != (a + b) / 2 + 1)
            return ab(i, a, (a + b) / 2);
        else
            return ab(i, (a + b) / 2, b);
  }
public static void main(String[] args) {
        int[] i = { 1, 2, 3, 4, 6, 7, 8, 9 };
        int b = i.length;
        System.out.println(ab(i, 0, b - 1));
        int a = 100;
        Integer i1 = a;
        i1 = 111;
        Integer i2 = a;
        System.out.println("i1:"+i1+"  i2:"+i2);
        a = 200;
        System.out.println("i1:"+i1+"  i2:"+i2);
        
        for(int c = 0 ;c<10;c++) {
            System.out.println((Integer)c);
        }     
 }

UUID的使用

uuid+当前线程id
long tid = Thread.currentThread().getId();
String uuid = UUID.randomUUID()+"@"+tid;

String类的使用

//四舍五入保留2位小数
String.format("%.2f", 3.1455926)
//整数部分不够4位前边补0
String.format("%04d", 333)

数组拷贝

数组拷贝过去
Long[] l1= {1l,3l,5l,7l,9l};
Long[] l2=Arrays.copyOf(l1, l1.length);

拷贝数组的一部分
Long[] l1= {1l,3l,5l,7l,9l};
Long[] l3=new Long[6];
从数组l1的1角标开始，到l3数组的0开始拷贝3个数据
System.arraycopy(l1, 1, l3, 0, 3);

后台判断是否是Ajax请求

public static Boolean isAjaxSubmit(HttpServletRequest request) {
  return "XMLHttpRequest".equals(request.getHeader("X-Requested-With"));
}