我正在尝试用 arraylists 替换我拥有的数组，这样我就不必担心管理数组并且可以清理我的代码。我只是自学了数组列表，所以我遇到了一些问题。主要在我所有的“集合”和“获取”所在的这些类中。我认为我的语法不正确，因为我收到了 ArrayList/String 冲突错误。基本上试图得到：
public static ArrayList<Resource> importResourcesFromXML(String documentLocation)
从 XML 文档中导入资源数组列表。我还想将 Resources 中的数组和 T_Resources 中的数组也转换为数组列表。这是我到目前为止的代码，我相信我已经正确实现了资源，但可以使用其他两个帮助来正确显示 XML 资源。
编辑：如果可能的话，我想完全消除数组并用数组列表替换它。我想尝试避免将数组转换为数组列表。
import java.util.ArrayList;
public class Resources {
//private static final int MAX_SUBJECTS = 20;
private String title;
private String description;
private Identifier identifier;
ArrayList<Subject> subject = new ArrayList<Subject>();
//private int subjectCount;
public Resources() {
title = "unknown title";
description = "unknown description";
identifier = null;
//subjects = new Subject[MAX_SUBJECTS];
//subjectCount = 0;
}
public void setTitle(String newTitle) {
title = newTitle;
}
public String getTitle() {
return title;
}
public void setDescription(String newDescription) {
description = newDescription;
}
public String getDescription() {
return description;
}
public void setIdentifier(Identifier newIdentifier) {
identifier = newIdentifier;
}
public Identifier getIdentifier() {
return identifier;
}
public void addSubject(Subject newSubject) {
subject.add(newSubject);
}
public ArrayList<Subject> getSubjects() {
//Subject[] result = new Subject[subjectCount];
//System.arraycopy(subjects, 0, result, 0, subjectCount);
return subject;
}
}
public class ResourceImporter {
// This operation loads the XML document specified by the document location, which can a file or a URL,
// and returns a reference to the document. If the operation cannot successfully load the document
// the operation returns the null reference.
//
private static Document loadXMLDocument(String documentLocation) {
// The XML document.
//
Document documentIn = null;
// The parser that reads in an XML files.
//
DocumentBuilder parser = null;
// Pull the document
//
try {
// Obtain a document parser.
//
DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
builderFactory.setNamespaceAware(true);
parser = builderFactory.newDocumentBuilder();
documentIn = parser.parse(documentLocation);
} catch (ParserConfigurationException p) {
System.out.println("Error creating parser.");
System.out.println(" " + p.getMessage());
} catch (SAXException s) {
System.out.println("Document is not well formed.");
System.out.println(" " + s.getMessage());
} catch (IOException i) {
System.out.println("Error accessing the file.");
System.out.println(" " + i.getMessage());
} catch (Exception e) {
System.out.println("Unknown error occurred.");
System.out.println(" " + e.getMessage());
}
return documentIn;
}
public static ArrayList<Resource> importResourcesFromXML(String documentLocation) {
ArrayList<Resource> resource = new ArrayList<Resource>();
Document doc;
Element resourceElement;
Element titleElement;
String title;
Element descriptionElement;
String description;
Element identifierElement;
String identifiers;
Element urlElement;
String url;
NodeList subjectList;
Element subjectElement;
String subjects;
Element categoryElement;
String category;
Element subcategoryElement;
String subcategory;
doc = loadXMLDocument(documentLocation);
resourceElement = (Element)doc.getElementsByTagName("resource").item(0);
if (resourceElement != null) {
titleElement = (Element)resourceElement.getElementsByTagName("title").item(0);
resource.setTitle( titleElement == null ? "unknown" : titleElement.getTextContent() );
descriptionElement = (Element)resourceElement.getElementsByTagName("description").item(0);
resource.setDescription( descriptionElement == null ? "unknown" : descriptionElement.getTextContent() );
identifierElement = (Element)resourceElement.getElementsByTagName("identifier").item(0);
if (identifierElement != null) {
Identifier identifier = new Identifier();
urlElement = (Element)identifierElement.getElementsByTagName("url").item(0);
identifier.setURL( urlElement == null ? "unknown" : urlElement.getTextContent() );
resource.setIdentifier(identifier);
subjectElement = (Element)resourceElement.getElementsByTagName("subjects").item(0);
if (subjectElement != null) {
subjectList = subjectElement.getElementsByTagName("subject");
for (int i=0; i < subjectList.getLength(); ++i) {
Subject subject = new Subject();
subjectElement = (Element)subjectList.item(i);
categoryElement = (Element)subjectElement.getElementsByTagName("category").item(0);
subject.setCategory( categoryElement == null ? "unknown" : categoryElement.getTextContent() );
subcategoryElement = (Element)subjectElement.getElementsByTagName("subcategory").item(0);
subject.setSubcategory( subcategoryElement == null ? "unknown" :subcategoryElement.getTextContent() );
resource.addSubject(subject);
}
}
}
}
return resource;
}
}
import java.util.ArrayList;
public class T_Resources {
public static void main(String[] args) {
ArrayList<Resource> resource = ResourceImporter.importResourcesFromXML("http://free1.ed.gov/xml/gemexport.xml");
displayResources(resource);
}
private static void displayResources(ArrayList<Resource> resource) {
ArrayList<Subject> subjects;
System.out.println(resource.getTitle());
System.out.println(resource.getDescription());
System.out.println(resource.getIdentifier().getURL());
subjects = resource.getSubjects();
for (int i=0; i < subjects.size(); ++i) {
System.out.println(subjects.getCategory() + " :: " + subjects.getSubcategory());
}
System.out.println();
}
}
public class Subject {
private String category;
private String subcategory;
public Subject() {
String category = "unknown";
String subcategory = "unknown";
}
public Subject(Subject subject) {
category = subject.category;
subcategory = subject.subcategory;
}
public void setCategory(String newCategory) {
category = (newCategory == null) ? "unknown" : newCategory;
}
public String getCategory() {
return category;
}
public void setSubcategory(String newSubcategory) {
subcategory = newSubcategory;
}
public String getSubcategory() {
return subcategory;
}
}
public class Identifier {
private String url;
public Identifier() {
url = "unknown";
}
public void setURL(String newURL) {
url = newURL;
}
public String getURL() {
return url;
}
}