Android面试题问答整理

public class Person {private Integer id;private String name;private Short age;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Short getAge() {return age;}public void setAge(Short age) {this.age = age;}}（1）使用SAX读取XML文件；它采用的是事件驱动，并不需要解析完整个文档，速度快并且占用内存少。需要为SAX提供实现ContentHandler接口的类。PersonDefaultHandler.javaimport java.util.ArrayList;import java.util.List;import org.xml.sax.Attributes;import org.xml.sax.SAXException;import org.xml.sax.helpers.DefaultHandler;import com.sinber.domain.Person;public class PersonDefaultHandler extends DefaultHandler {private List persons;private Person person ; //记录当前personprivate String perTag; //记录前一个标签的名称/*** 重写父类的开始文档方法。用于初始化*/@Overridepublic void startDocument() throws SAXException {persons = new ArrayList();}@Overridepublic void startElement(String uri, String localName, String qName,Attributes attributes) throws SAXException {if(“person”.equals(localName)){Integer id = new Integer(attributes.getValue(0)); //取idperson = new Person();person.setId(id);}perTag = localName;}/**参数：* ch 整个XML字符串* start 节点值在整个XML字符串中的索引位置* length 节点值的长度*/@Overridepublic void characters(char[] ch, int start, int length)throws SAXException {if(perTag!=null){String data = new String(ch,start,length);if(“name”.equals(perTag)){person.setName(data);}else if(“age”.equals(perTag)){person.setAge(new Short(data));}}}@Overridepublic void endElement(String uri, String localName, String qName)throws SAXException {if(“person”.equals(localName)){persons.add(person);person = null;}perTag = null;}public List getPersons() {return persons;}}SAXPerson.javaimport java.io.InputStream;import java.util.List;import javax.xml.parsers.SAXParser;import javax.xml.parsers.SAXParserFactory;import com.sinber.domain.Person;public class SAXPerson{public static List getPerson() throws Exception{//通过类装载器获取文件InputStream inStream = SAXPersonService.class.getClassLoader().getResourceAsStream(“person.xml”);SAXParserFactory factory = SAXParserFactory.newInstance();SAXParser saxParser = factory.newSAXParser();PersonDefaultHandler handler = new PersonDefaultHandler();saxParser.parse(inStream, handler);inStream.close();return handler.getPersons();}}（2）DOM解析XML文件时，会将XML文件的所有内容读取到内存中，然后允许您使用DOM API遍历XML树、检索所需的数据。DOMPerson.javaimport java.io.InputStream;import java.util.ArrayList;import java.util.List;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import org.w3c.dom.Document;import org.w3c.dom.Element;import org.w3c.dom.Node;import org.w3c.dom.NodeList;import com.sinber.domain.Person;public class DOMPerson {public static List getPerson() throws Exception{List pers = new ArrayList();InputStream inStream = SAXPersonService.class.getClassLoader().getResourceAsStream(“person.xml”);DocumentBuilderFactory factory =DocumentBuilderFactory.newInstance();DocumentBuilder builder = factory.newDocumentBuilder();Document dom = builder.parse(inStream);Element root = dom.getDocumentElement();NodeList persons = root.getElementsByTagName(“person”);for(int i=0;i<persons.getLength();i++){Element personNode =(Element)persons.item(i);Person person = new Person();person.setId(new Integer(personNode.getAttribute("id")));NodeList childNodes = personNode.getChildNodes();for(int j=0;j<childNodes.getLength();j++){Node childNode = childNodes.item(j);if(childNode.getNodeType()==Node.ELEMENT_NODE){Element element = (Element)childNode;if("name".equals(childNode.getNodeName())){person.setName(new String(element.getFirstChild().getNodeValue()));}else if("age".equals(childNode.getNodeName())){person.setAge(new Short(element.getFirstChild().getNodeValue()));}}}pers.add(person);}inStream.close();return pers;}}（3）使用Pull解析器读取XML文件PullPerson.javaimport java.io.File;import java.io.FileOutputStream;import java.io.InputStream;import java.util.ArrayList;import java.util.List;import org.xmlpull.v1.XmlPullParser;import org.xmlpull.v1.XmlSerializer;import android.os.Environment;import android.util.Xml;import com.sinber.domain.Person;public class PullPerson {public static void save(List persons) throws Exception{XmlSerializer serializer = Xml.newSerializer();File file = new File(Environment.getExternalStorageDirectory(),”person.xml”);FileOutputStream outStream = new FileOutputStream(file);serializer.setOutput(outStream,”UTF-8″);serializer.startDocument(“UTF-8″, true);serializer.startTag(“”, “persons”);for(Person person:persons){serializer.startTag(“”, “person”); //personserializer.attribute(“”, “id”, “”+person.getId());serializer.startTag(“”, “name”); //nameserializer.text(person.getName());serializer.endTag(“”, “name”); //nameserializer.startTag(“”, “age”); //ageserializer.text(person.getAge().toString());serializer.endTag(“”, “age”);//ageserializer.endTag(“”, “person”); //person}serializer.endTag(“”, “persons”);serializer.endDocument();outStream.close();}public static List getPersons() throws Exception{List persons = null;Person person = null;XmlPullParser parser= Xml.newPullParser();InputStream inStream = PullPersonService.class.getClassLoader().getResourceAsStream(“person.xml”);parser.setInput(inStream, “UTF-8″);int eventType = parser.getEventType(); //触发第一个事件while(eventType!=XmlPullParser.END_DOCUMENT){switch(eventType){case XmlPullParser.START_DOCUMENT:persons = new ArrayList();break;case XmlPullParser.START_TAG: //开始元素事件if(“person”.equals(parser.getName())){person = new Person();person.setId(new Integer(parser.getAttributeValue(0)));}else if(person!=null){if(“name”.equals(parser.getName())){person.setName(parser.nextText());}else if(“age”.equals(parser.getName())){person.setAge(new Short(parser.nextText()));}}break;case XmlPullParser.END_TAG: //结束元素事件if(“person”.equals(parser.getName())){persons.add(person);person = null;}break;default:break;}eventType = parser.next();}return persons;}}以上三种方式任选其一即可。

Node.javapublic class Node {private Integer count;private Node nextNode;public Node(){}public Node(int count){this.count = new Integer(count);}public Integer getCount() {return count;}public void setCount(Integer count) {this.count = count;}public Node getNextNode() {return nextNode;}public void setNextNode(Node nextNode) {this.nextNode = nextNode;}}ReverseSingleLink.javapublic class ReverseSingleLink {public static Node revSingleLink(Node head){if(head == null){ //链表为空不能逆序return head;}if(head.getNextNode()==null){ //如果只有一个结点，当然逆过来也是同一个return head;}Node rhead = revSingleLink(head.getNextNode());head.getNextNode().setNextNode(head);head.setNextNode(null);return rhead;}public static void main(String[] args){Node head = new Node(0);Node temp1 = null,temp2 = null;for(int i=1;i<100;i++){temp1 = new Node(i);if(i==1){head.setNextNode(temp1);}else{temp2.setNextNode(temp1);}temp2 = temp1;}head = revSingleLink(head);while(head!=null){head = head.getNextNode();}}}