关于java.lang.Math类的round() ,floor() ,ceil() 方法

突然想起上次做题的时候我搞错了......我一直在误区中......于是写在这里警示一下。
其实许多大牛对于这个已经说了无数遍了，我就不多说了。

round()方法：

static long round(double a)
          Returns the closest long to the argument.
static int round(float a)
          Returns the closest int to the argument.

查看jdk文档，看看这几个方法到底是怎么回事。

public static long round(double a)
Returns the closest long to the argument. The result is rounded to an integer by adding 1/2, taking the floor of the result, and casting the result to type long. In other words, the result is equal to the value of the expression: 

(long)Math.floor(a + 0.5d)
Special cases: 

If the argument is NaN, the result is 0. 
If the argument is negative infinity or any value less than or equal to the value of Long.MIN_VALUE, the result is equal to the value of Long.MIN_VALUE. 
If the argument is positive infinity or any value greater than or equal to the value of Long.MAX_VALUE, the result is equal to the value of Long.MAX_VALUE.

public static int round(float a)
Returns the closest int to the argument. The result is rounded to an integer by adding 1/2, taking the floor of the result, and casting the result to type int. In other words, the result is equal to the value of the expression: 

(int)Math.floor(a + 0.5f)

Special cases: 

If the argument is NaN, the result is 0. 
If the argument is negative infinity or any value less than or equal to the value of Integer.MIN_VALUE, the result is equal to the value of Integer.MIN_VALUE. 
If the argument is positive infinity or any value greater than or equal to the value of Integer.MAX_VALUE, the result is equal to the value of Integer.MAX_VALUE.

ceil()和floor()方法：

public static double ceil(double a)
Returns the smallest (closest to negative infinity) double value that is greater than or equal to the argument and is equal to a mathematical integer. Special cases: 
If the argument value is already equal to a mathematical integer, then the result is the same as the argument. 
If the argument is NaN or an infinity or positive zero or negative zero, then the result is the same as the argument. 
If the argument value is less than zero but greater than -1.0, then the result is negative zero.
Note that the value of Math.ceil(x) is exactly the value of -Math.floor(-x). 

public static double floor(double a)
Returns the largest (closest to positive infinity) double value that is less than or equal to the argument and is equal to a mathematical integer. Special cases: 
If the argument value is already equal to a mathematical integer, then the result is the same as the argument. 
If the argument is NaN or an infinity or positive zero or negative zero, then the result is the same as the argument.

基础很重要，有些东西不是相当然而，万丈高楼还的平地起！！