Java 四捨五入至小數第 n 位

//欲四捨五入的數字
double y = 1.890784;

//設定要到小數第 3 位
int n = 3;

//執行四捨五入
double x = new BigDecimal(y).setScale(n, BigDecimal.ROUND_HALF_UP).doubleValue();

//印出結果
System.out.println(x);

//不要有科學記號出現的方法
double x = new BigDecimal(y).setScale(n, BigDecimal.ROUND_HALF_UP).toPlainString();

Java XPath 使用範例

XML 範例：books.xml

<?xml version="1.0" encoding="UTF-8"?>

<LIBRARY>

    <BOOKS>

        <BOOK isbn="ABCD7327923">

            <NAME>Java Programing</NAME>

            <SUBJECT>Java J2EE</SUBJECT>

            <AUTHORS>

                <AUTHOR>Tuna TORE</AUTHOR>

                <AUTHOR>Linus Torvalds</AUTHOR>

                <AUTHOR>James Gosling</AUTHOR>

            </AUTHORS>

        </BOOK>

        <BOOK isbn="DFGH09093232">

             <NAME>XPATH for Dummies</NAME>

           <SUBJECT> XPATH development</SUBJECT>

            <AUTHORS>

                <AUTHOR>Linus Torvalds</AUTHOR>

                <AUTHOR>John Hawking</AUTHOR>

            </AUTHORS>

        </BOOK>

        <BOOK isbn="DSKL2393A">

            <NAME>J2EE Patterns</NAME>

            <SUBJECT>Design Patterns</SUBJECT>

            <AUTHORS>

                <AUTHOR>Aka Tuna</AUTHOR>

            </AUTHORS>

        </BOOK>

    </BOOKS>

    <DVDS>

        <DVD id="123456">

            <NAME>Music DVD</NAME>

            <CONTENT>Music</CONTENT>

            <AUTHORS>

                <AUTHOR>James Gosling</AUTHOR>

                <AUTHOR>Bill Gates</AUTHOR>

            </AUTHORS>

        </DVD>

        <DVD id="3213324">

            <NAME>Natural Science</NAME>

            <CONTENT>Science</CONTENT>

            <AUTHORS>

                <AUTHOR>John Green</AUTHOR>

                <AUTHOR>Bill Gates</AUTHOR>

            </AUTHORS>

        </DVD>

        <DVD id="4353534">

            <NAME>Rally</NAME>

            <CONTENT>Race</CONTENT>

            <AUTHORS>

                <AUTHOR>Tuna</AUTHOR>

            </AUTHORS>

        </DVD>

    </DVDS>

</LIBRARY>

程式範例： XpathTest.java

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.xpath.XPath;

import javax.xml.xpath.XPathConstants;

import javax.xml.xpath.XPathExpression;

import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;

import org.w3c.dom.NodeList;

public class XPathTest {

    public static void main(String[] args) throws Exception {

        //loading the XML document from a file

        DocumentBuilderFactory builderfactory = DocumentBuilderFactory.newInstance();

        builderfactory.setNamespaceAware(true);

        DocumentBuilder builder = builderfactory.newDocumentBuilder();

        Document xmlDocument = builder.parse("src\\books.xml");

        XPathFactory factory = javax.xml.xpath.XPathFactory.newInstance();

        XPath xPath = factory.newXPath();

        //getting the name of the book having an isbn number == ABCD7327923

        String isbnNum = "ABCD7327923";

        XPathExpression xPathExpression = xPath.compile("//LIBRARY//BOOKS//BOOK[@isbn='" + isbnNum + "']//NAME");

        String nameOfTheBook = xPathExpression.evaluate(xmlDocument, XPathConstants.STRING).toString();

        System.out.println("name of the Book ---> " + nameOfTheBook);

        //getting all authors for the book having an isbn number == ABCD7327923

        xPathExpression = xPath.compile("//LIBRARY//BOOKS//BOOK[@isbn='" + isbnNum + "']//AUTHORS//AUTHOR");

        NodeList nodeListBook = (NodeList) xPathExpression.evaluate(xmlDocument, XPathConstants.NODESET);

        System.out.println("Total number of authors for the book " + nameOfTheBook + " is --> "

                + nodeListBook.getLength());

        for (int index = 0; index < nodeListBook.getLength(); index++) {

            String author = nodeListBook.item(index).getTextContent();

            System.out.println("Author " + (index + 1) + " ---> " + author);

        }

        //getting all tags for the dvd having id == 3213324

        String dvdID = "3213324";

        xPathExpression = xPath.compile("//LIBRARY//DVDS//DVD[@id='" + dvdID + "']");

        NodeList nodeDVD = (NodeList) xPathExpression.evaluate(xmlDocument, XPathConstants.NODESET);

        NodeList nodeListForDVD = nodeDVD.item(0).getChildNodes();

        for (int index = 0; index < nodeDVD.item(0).getChildNodes().getLength(); index++) {

            String tagName = nodeListForDVD.item(index).getNodeName();

            String tagValue = nodeListForDVD.item(index).getTextContent();

            if (!tagName.equals("#text")) //handling empty comment (#text)

                System.out.println(tagName + " value ---> " + tagValue);

        }

    }

}

執行結果：
name of the Book: Java Programing
Total number of authors for the book Java Programing is --> 3
Author 1: Tuna TORE
Author 2: Linus Torvalds
Author 3: James Gosling
NAME value: Natural Science
CONTENT value: Science
AUTHORS value:
                John Green
                Bill Gates

參考文件：http://tunatore.wordpress.com/2011/05/20/how-to-use-xpath-i-java-simple-example/