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原文地址:http://bloodredsun.com/?p=320
另一篇文章:What Every Computer Scientist Should Know About Floating-Point Arithmetichttp://download.oracle.com/docs/cd/E19957-01/806-3568/ncg_goldberg.html
My current client is in the middle of hiring some Java developers and as I
mentioned earlier in March (Interviewing – the importance of PASSION!) I’ve been doing some of the interviewing. One of the things we’ve done is to create a technical task to see how the candidates actually code. It’s a simple exercise that requires them to think through some of the basics of financial operations and one thing that has surprised me has been the common use of doubles to represent financial values. It’s been highlighted for some time that this is not a great thing to do but someone actually challenged me to show that it wasn’t.
So here we go…
view plaincopy to clipboardprint?
package com.bloodredsun;
public class DoubleOperation {
public static void main(String[] args) {
double t1 = 10.266d;
double t2 = 10.0d;
//Outputs 0.266
System.out.println(t1-t2);
double h1 = 100.266d;
double h2 = 100.0d;
//Outputs 0.26600000000000534
System.out.println(h1-h2);
}
}
Ouch! That is not what we want but it is the classic behaviour of doubles. The inability to represent some decimals in the IEEE-754 format (as binary fractions) causes this. If we want correct precision the answer is to use BigDecimals but we have to remember to use Strings in the constructors or you end up with the same issues that you were trying to avoid.
view plaincopy to clipboardprint?
package com.bloodredsun;
import java.math.BigDecimal;
public class BigDecimalOperation {
public static void main(String[] args) {
BigDecimal t1 = new BigDecimal("10.266");
BigDecimal t2 = new BigDecimal("10.0");
//Outputs 0.266
System.out.println(t1.subtract(t2));
BigDecimal h1 = new BigDecimal("100.266");
BigDecimal h2 = new BigDecimal("100.0");
//Outputs 0.266
System.out.println(h1.subtract(h2));
}
}
That’s great but wouldn’t it be nice to use the normal operators rather than the overly-verbose method calls for the mathematical operations.
Now there is no way that we can do this in Java but if we let ourselves use another language on the JVM…
view plaincopy to clipboardprint?
package com.bloodredsun
object ScalaBigDecimalOperation {
def main (args: Array[String]) {
var t1 = BigDecimal("10.266")
var t2 = BigDecimal("10.0")
//Outputs 0.266
println(t1 - t2)
var h1 = BigDecimal("100.266")
var h2 = BigDecimal("100.0")
//Outputs 0.266
println(h1 - h2)
}
}
Scala FTW!
PS if you want to know more about floating point operations have a read of What Every Computer Scientist Should Know About Floating-Point Arithmetic
另一篇文章:What Every Computer Scientist Should Know About Floating-Point Arithmetichttp://download.oracle.com/docs/cd/E19957-01/806-3568/ncg_goldberg.html
My current client is in the middle of hiring some Java developers and as I
mentioned earlier in March (Interviewing – the importance of PASSION!) I’ve been doing some of the interviewing. One of the things we’ve done is to create a technical task to see how the candidates actually code. It’s a simple exercise that requires them to think through some of the basics of financial operations and one thing that has surprised me has been the common use of doubles to represent financial values. It’s been highlighted for some time that this is not a great thing to do but someone actually challenged me to show that it wasn’t.
So here we go…
view plaincopy to clipboardprint?
package com.bloodredsun;
public class DoubleOperation {
public static void main(String[] args) {
double t1 = 10.266d;
double t2 = 10.0d;
//Outputs 0.266
System.out.println(t1-t2);
double h1 = 100.266d;
double h2 = 100.0d;
//Outputs 0.26600000000000534
System.out.println(h1-h2);
}
}
Ouch! That is not what we want but it is the classic behaviour of doubles. The inability to represent some decimals in the IEEE-754 format (as binary fractions) causes this. If we want correct precision the answer is to use BigDecimals but we have to remember to use Strings in the constructors or you end up with the same issues that you were trying to avoid.
view plaincopy to clipboardprint?
package com.bloodredsun;
import java.math.BigDecimal;
public class BigDecimalOperation {
public static void main(String[] args) {
BigDecimal t1 = new BigDecimal("10.266");
BigDecimal t2 = new BigDecimal("10.0");
//Outputs 0.266
System.out.println(t1.subtract(t2));
BigDecimal h1 = new BigDecimal("100.266");
BigDecimal h2 = new BigDecimal("100.0");
//Outputs 0.266
System.out.println(h1.subtract(h2));
}
}
That’s great but wouldn’t it be nice to use the normal operators rather than the overly-verbose method calls for the mathematical operations.
Now there is no way that we can do this in Java but if we let ourselves use another language on the JVM…
view plaincopy to clipboardprint?
package com.bloodredsun
object ScalaBigDecimalOperation {
def main (args: Array[String]) {
var t1 = BigDecimal("10.266")
var t2 = BigDecimal("10.0")
//Outputs 0.266
println(t1 - t2)
var h1 = BigDecimal("100.266")
var h2 = BigDecimal("100.0")
//Outputs 0.266
println(h1 - h2)
}
}
Scala FTW!
PS if you want to know more about floating point operations have a read of What Every Computer Scientist Should Know About Floating-Point Arithmetic
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2012-04-24 11:06 1149只要这样配置好久能使用gmail了 <bean id= ... -
log4j 常用配置
2012-03-22 21:02 1100原文地址:http://www.benmccann.com/d ... -
Dependency Injection - An Introductory Tutorial - Part 1
2012-02-20 10:57 1210原文地址:http://code.google.com/p/j ... -
struts2 排除拦截部分路径
2011-11-30 13:27 5785情况:在web.xml中配置一个servlet映射路径为/te ... -
java image scale
2011-07-20 13:47 931http://code.google.com/p/java-i ... -
实现自定义截取图片
2011-07-13 17:30 1112几种插件: http://odyniec.net/projec ... -
jms基础概念和应用场景
2011-07-01 13:55 1606原文地址:http://blog.csdn.net/KimmK ... -
Envers –tracked your Entity Objects
2011-06-29 09:05 1584原文地址:http://get2java.wordpress. ... -
JSON Compression algorithms: HPack VS CJSON
2011-06-28 17:24 3164总结:HPack 优于 CJSON json1 json2 ... -
http://jbaruch.wordpress.com/2011/06/22/unified-logging-using-slf4j/
2011-06-27 10:48 1213原文地址:http://jbaruch.wordpress.c ... -
Sturts2 全局异常日志
2011-06-25 10:50 1814原文地址:http://www.brucephillips.n ... -
eclipse的build与clean
2011-06-22 09:01 1582现象:无论怎么改变代码,程序的行为始终不变,一直报错。。。。 ... -
jfreechart 图标各部分名字
2011-06-09 19:57 845图标各部分名字 -
jfreechart 自定义饼图颜色
2011-06-09 18:52 4911关键代码: private static class Pi ... -
jfreechart demo 代码
2011-06-07 18:33 2963jfreechart 官方demo 源代码 -
jfreechart 中文问题
2011-06-07 16:52 953基本如果将jfreechart生成图片的字体多改成中文的字体就 ... -
SVN 安装
2011-05-30 15:45 1023collabnet svn 现在出了整和的SVN EDGE。这 ... -
amazon 云计算
2011-05-28 21:45 1088最近看了amazon的云计算 ... -
c3p0 java.lang.Exception: DEBUG -- CLOSE BY CLIENT STACK TRACE
2011-05-28 16:07 1591修改日志级别为info http://hi.baidu.com ... -
mybatis打印sql
2011-05-09 15:03 20017mybatis默认使用log4j,当有self4j这个日志ja ...
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