本文来源于：http://swiftlet.net/archives/1369
floor原意：地板。Math.floor函数是求一个浮点数的地板，就是求一个最接近它的整数，它的值小于或等于这个浮点数。看下面的例子：
|
|
public
class
Test
{
public
static
void
main
(
String
[
]
args
)
{
System
.
out
.
println
(
"Math.floor(-1.1): "
+
Math
.
floor
(
-
1.1
)
)
;
System
.
out
.
println
(
"Math.floor(-1.5): "
+
Math
.
floor
(
-
1.5
)
)
;
System
.
out
.
println
(
"Math.floor(-1.6): "
+
Math
.
floor
(
-
1.6
)
)
;
System
.
out
.
println
(
"Math.floor(0.1): "
+
Math
.
floor
(
0.1
)
)
;
System
.
out
.
println
(
"Math.floor(0.5): "
+
Math
.
floor
(
0.5
)
)
;
System
.
out
.
println
(
"Math.floor(0.6): "
+
Math
.
floor
(
0.6
)
)
;
System
.
out
.
println
(
"Math.floor(1.1): "
+
Math
.
floor
(
1.1
)
)
;
System
.
out
.
println
(
"Math.floor(1.5): "
+
Math
.
floor
(
1.5
)
)
;
System
.
out
.
println
(
"Math.floor(1.6): "
+
Math
.
floor
(
1.6
)
)
;
}
}
|
结果为：
Math.floor(-1.1): -2.0
Math.floor(-1.5): -2.0
Math.floor(-1.6): -2.0
Math.floor(0.1): 0.0
Math.floor(0.5): 0.0
Math.floor(0.6): 0.0
Math.floor(1.1): 1.0
Math.floor(1.5): 1.0
Math.floor(1.6): 1.0
Math.ceil函数讲解
ceil愿意：天花板。Math.ceil函数执行的是向上取整计算，它返回的是大于或等于函数参数，并且与之最接近的整数。看下面的例子：
| |
public
class
Test
{
public
static
void
main
(
String
[
]
args
)
{
System
.
out
.
println
(
"Math.ceil(-1.1): "
+
Math
.
ceil
(
-
1.1
)
)
;
System
.
out
.
println
(
"Math.ceil(-1.5): "
+
Math
.
ceil
(
-
1.5
)
)
;
System
.
out
.
println
(
"Math.ceil(-1.6): "
+
Math
.
ceil
(
-
1.6
)
)
;
System
.
out
.
println
(
"Math.ceil(0.1): "
+
Math
.
ceil
(
0.1
)
)
;
System
.
out
.
println
(
"Math.ceil(0.5): "
+
Math
.
ceil
(
0.5
)
)
;
System
.
out
.
println
(
"Math.ceil(0.6): "
+
Math
.
ceil
(
0.6
)
)
;
System
.
out
.
println
(
"Math.ceil(1.1): "
+
Math
.
ceil
(
1.1
)
)
;
System
.
out
.
println
(
"Math.ceil(1.5): "
+
Math
.
ceil
(
1.5
)
)
;
System
.
out
.
println
(
"Math.ceil(1.6): "
+
Math
.
ceil
(
1.6
)
)
;
}
}
|
结果为：
Math.ceil(-1.1): -1.0
Math.ceil(-1.5): -1.0
Math.ceil(-1.6): -1.0
Math.ceil(0.1): 1.0
Math.ceil(0.5): 1.0
Math.ceil(0.6): 1.0
Math.ceil(1.1): 2.0
Math.ceil(1.5): 2.0
Math.ceil(1.6): 2.0
Math.rint函数讲解
Math.rint函数返回最接近参数的整数，如果有2个数同样接近，则返回偶数的那个。
| |
public
class
Test
{
public
static
void
main
(
String
[
]
args
)
{
System
.
out
.
println
(
"Math.rint(-1.1): "
+
Math
.
rint
(
-
1.1
)
)
;
System
.
out
.
println
(
"Math.rint(-1.5): "
+
Math
.
rint
(
-
1.5
)
)
;
System
.
out
.
println
(
"Math.rint(-1.6): "
+
Math
.
rint
(
-
1.6
)
)
;
System
.
out
.
println
(
"Math.rint(0.1): "
+
Math
.
rint
(
0.1
)
)
;
System
.
out
.
println
(
"Math.rint(0.5): "
+
Math
.
rint
(
0.5
)
)
;
System
.
out
.
println
(
"Math.rint(0.6): "
+
Math
.
rint
(
0.6
)
)
;
System
.
out
.
println
(
"Math.rint(1.1): "
+
Math
.
rint
(
1.1
)
)
;
System
.
out
.
println
(
"Math.rint(1.5): "
+
Math
.
rint
(
1.5
)
)
;
System
.
out
.
println
(
"Math.rint(1.6): "
+
Math
.
rint
(
1.6
)
)
;
}
}
|
结果为：
Math.rint(-1.1): -1.0
Math.rint(-1.5): -2.0
Math.rint(-1.6): -2.0
Math.rint(0.1): 0.0
Math.rint(0.5): 0.0
Math.rint(0.6): 1.0
Math.rint(1.1): 1.0
Math.rint(1.5): 2.0
Math.rint(1.6): 2.0
Math.round函数讲解
round方法，它表示"四舍五入"，算法为Math.floor(x+0.5)，即将原来的数字加上0.5后再向下取整
|
|
public
class
Test
{
public
static
void
main
(
String
[
]
args
)
{
System
.
out
.
println
(
"Math.round(-1.1): "
+
Math
.
round
(
-
1.1
)
)
;
System
.
out
.
println
(
"Math.round(-1.5): "
+
Math
.
round
(
-
1.5
)
)
;
System
.
out
.
println
(
"Math.round(-1.6): "
+
Math
.
round
(
-
1.6
)
)
;
System
.
out
.
println
(
"Math.round(0.1): "
+
Math
.
round
(
0.1
)
)
;
System
.
out
.
println
(
"Math.round(0.5): "
+
Math
.
round
(
0.5
)
)
;
System
.
out
.
println
(
"Math.round(0.6): "
+
Math
.
round
(
0.6
)
)
;
System
.
out
.
println
(
"Math.round(1.1): "
+
Math
.
round
(
1.1
)
)
;
System
.
out
.
println
(
"Math.round(1.5): "
+
Math
.
round
(
1.5
)
)
;
System
.
out
.
println
(
"Math.round(1.6): "
+
Math
.
round
(
1.6
)
)
;
}
}
|
结果为：
Math.round(-1.1): -1
Math.round(-1.5): -1
Math.round(-1.6): -2
Math.round(0.1): 0
Math.round(0.5): 1
Math.round(0.6): 1
Math.round(1.1): 1
Math.round(1.5): 2
Math.round(1.6): 2
Math.floor()就是下取整，返回一个浮点型值，Math.ceil()是上取整，也返回一个浮点型值，Math.round()，四舍五入，返回一个整型值，Math.rint()，
返回最接近参数的整数，如果有2个数同样接近，则返回偶数的那个，返回一个浮点型值
