每個 Java 開發人員都應該知道的最佳數學庫

	import org.apache.commons.math3.fraction.Fraction;
	public class Demo {

		public static void main(String[] args) {
			/*
			 * double[] n = { 1.1, 1.2, 1.3, 1.4, 2.1, 2.2, -2.35, 100.09 };
			 *
			 * for (double d : n) System.out.printf("12 : 445", d, new BigFraction(d,
			 * 0.00000002D, 10000));
			 */

			//In Java, assuming I have a double variable called decimal with the assigned value of 0.333,
			//how would I display this as a "proper", formatted fraction -
			//with the numerator over the denominator separated with a straight line (instead of simply displaying 1/3)?
			Fraction a = new Fraction(1, 10);
			Fraction b = new Fraction(0.99);
			System.out.println("Result:" + " " + a.add(b));
		   // I need to add up a series of fractions, e.g. 1/2 + 1/3 + 1/4 + ..., and return a double. How can I avoid or minimize the round off error?
	//
	//        An alternative if you want to preserve accuracy,
	//        and don't want to rely on the precision settings of BigDecimal, is to use the Apache Fractions library:

			Fraction grf1 = Fraction.getReducedFraction(1, 2);
			grf1 = grf1.add(Fraction.getReducedFraction(1, 2));
			grf1 = grf1.add(Fraction.getReducedFraction(1, 3));
			System.out.println(grf1);
			System.out.println(grf1.doubleValue());
		}
	}
	```

3. 在 Windows 中開啟命令提示符。
4. 編譯它：`javac -cp "commons-math3-3.6.1.jar" Demo.java`。
5. 執行它：`java -cp ".;commons-math3-3.6.1.jar" Demo`。

	輸出：

	```text
	Result: 109 / 100
	4 / 3
	1.3333333333333333
	```

如果你有任何困惑，我們也建立了一個演示 gif。

![從 Windows 中的命令列介面 shell 配置和執行你的庫程式](</img/Java/configure-and-run-your-library-program-from-command-line-interface-shell-in-windows.webp>)

## Apache Commons 演示數學程式

以下程式碼塊將在定義的範圍內建立隨機數和字串。你可以使用 Apache Commons 使用字母和數字來建立演算法。

它使用：`apache import org.apache.commons.lang3.RandomStringUtils;` `commons-lang3-3.12.0` `jar` 檔案（也附加在 zip 資料夾中）。

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程式碼：

```java
/*Basic level random string and random numeric value generator in the given range.abstract
Note this is for the demonstration of how to use a particular library*/
import org.apache.commons.lang3.RandomStringUtils;

public class BestJavaMathLibrary {
  public static void main(String[] args) {
    String rn1 = RandomStringUtils.randomNumeric(50);
    System.out.println(rn1);
    String rs1 = RandomStringUtils.randomAlphabetic(50);

    System.out.println(rs1);
  }
}

80511636875416144724783964293309510956685562561281
sXSlFJCVOxeaAhVAdEITZfynFdatqdvtAQPJVSrVTHlxZrjPYZ

import java.util.Collection;
import org.jscience.mathematics.number.LargeInteger;
import org.jscience.mathematics.number.Rational;

public class JScienceDemo {
  public static void main(String[] args) {
    // your code here
  }
}