在Jakarta Commons中，专门处理数学计算的类分别可以在两个地方找到：一是Commons Lang的org.apache.commons.lang.math包中，二是在Commons Math这个单独的子项目中。由于后者主要是处理复数、矩阵等，相对使用比较少，在我的笔记中就只简单讲讲Commons Lang中的math包。对后者感兴趣的可以看看
http://jakarta.apache.org/commons/math/
org.apache.commons.lang.math包中共有10个类，这些类可以归纳成四组：
1- 处理分数的Fraction类；
2- 处理数值的NumberUtils类；
3- 处理数值范围的Range、NumberRange、IntRange、LongRange、FloatRange、DoubleRange类；
4- 处理随机数的JVMRandom和RandomUtils类。
下面我举个例子分别说明上述四组的使用方法：
package sean.study.jakarta.commons.lang;
import org.apache.commons.lang.ArrayUtils;
import org.apache.commons.lang.BooleanUtils;
import org.apache.commons.lang.StringUtils;
import org.apache.commons.lang.math.DoubleRange;
import org.apache.commons.lang.math.Fraction;
import org.apache.commons.lang.math.NumberUtils;
import org.apache.commons.lang.math.RandomUtils;
import org.apache.commons.lang.math.Range;
public class LangMathUsage {
public static void main(String[] args) {
demoFraction();
demoNumberUtils();
demoNumberRange();
demoRandomUtils();
}
public static void demoFraction() {
System.out.println(StringUtils.center(" demoFraction ", 30, "="));
Fraction myFraction = Fraction.getFraction(144, 90);
// Fraction myFraction = Fraction.getFraction("1 54/90");
System.out.println("144/90 as fraction: " + myFraction);
System.out.println("144/90 to proper: " + myFraction.toProperString());
System.out.println("144/90 as double: " + myFraction.doubleValue());
System.out.println("144/90 reduced: " + myFraction.reduce());
System.out.println("144/90 reduced proper: "
+ myFraction.reduce().toProperString());
System.out.println();
}
public static void demoNumberUtils() {
System.out.println(StringUtils.center(" demoNumberUtils ", 30, "="));
System.out.println("Is 0x3F a number? "
+ StringUtils.capitalize(BooleanUtils.toStringYesNo(NumberUtils
.isNumber("0x3F"))) + ".");
double[] array = { 1.0, 3.4, 0.8, 7.1, 4.6 };
double max = NumberUtils.max(array);
double min = NumberUtils.min(array);
String arrayStr = ArrayUtils.toString(array);
System.out.println("Max of " + arrayStr + " is: " + max);
System.out.println("Min of " + arrayStr + " is: " + min);
System.out.println();
}
public static void demoNumberRange() {
System.out.println(StringUtils.center(" demoNumberRange ", 30, "="));
Range normalScoreRange = new DoubleRange(90, 120);
double score1 = 102.5;
double score2 = 79.9;
System.out.println("Normal score range is: " + normalScoreRange);
System.out.println("Is "
+ score1
+ " a normal score? "
+ StringUtils
.capitalize(BooleanUtils.toStringYesNo(normalScoreRange
.containsDouble(score1))) + ".");
System.out.println("Is "
+ score2
+ " a normal score? "
+ StringUtils
.capitalize(BooleanUtils.toStringYesNo(normalScoreRange
.containsDouble(score2))) + ".");
System.out.println();
}
public static void demoRandomUtils() {
System.out.println(StringUtils.center(" demoRandomUtils ", 30, "="));
for (int i = 0; i < 5; i++) {
System.out.println(RandomUtils.nextInt(100));
}
System.out.println();
}
}
以下是运行结果：
======== demoFraction ========
144/90 as fraction: 144/90
144/90 to proper: 1 54/90
144/90 as double: 1.6
144/90 reduced: 8/5
144/90 reduced proper: 1 3/5
====== demoNumberUtils =======
Is 0x3F a number? Yes.
Max of {1.0,3.4,0.8,7.1,4.6} is: 7.1
Min of {1.0,3.4,0.8,7.1,4.6} is: 0.8
====== demoNumberRange =======
Normal score range is: Range[90.0,120.0]
Is 102.5 a normal score? Yes.
Is 79.9 a normal score? No.
====== demoRandomUtils =======
75
63
40
21
92
以上就是Commons Lang的math包通常的用法。提一下NumberUtils.inNumber(String)方法，它会正确判断出给定的字符串是否是合法的数值，而我在前面的笔记中提到的StringUtils.isNumeric(String)只能判断一个字符串是否是由纯数字字符组成。Commons Lang的math包的各个类都还有很多实用的方法，远不止我在例子中用到的这些，如果你感兴趣，参照一下Commons Lang的Javadoc