Java 保留小数位数

如图就是保留四位（四舍五入）

Double aa = 0.5463785426872534867;
        aa = (double) Math.round(aa * 10000) / 10000;
        System.out.println(aa);

保留两位就是

Double aa = 0.5463785426872534867;
        aa = (double) Math.round(aa * 100) / 100;
        System.out.println(aa);

还有一种：

Double aa = 0.5463785426872534867;
        aa = (double) Math.round(aa * 10000) / 100;
        System.out.println(aa);