Android笔试(一)
<?xml version="1.0" encoding="UTF-8"?>?
<persons>?
<person?id="1">?
<name>张三</name>?
<age>22</age>?
</person>?
<person?id="2">?
<name>李四</name>?
<age>23</age>?
</person>?
</persons>定义一个名为Person的javaBean用于存放上面解析出来的xml内容publicclass?Person {
private?Integer id;
private?String name;
private?Short age;
public?Integer getId() {
return?id;
}
publicvoid?setId(Integer id) {
this.id?=?id;
}
public?String getName() {
return?name;
}
publicvoid?setName(String name) {
this.name?=?name;
}
public?Short getAge() {
return?age;
}
publicvoid?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;
publicclass?PersonDefaultHandler?extends?DefaultHandler {
private?List<Person>?persons;
private?Person person ;?//记录当前person
private?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
*/
@Override
publicvoid?startDocument()?throws?SAXException {
persons?=new?ArrayList<Person>();
}
@Override
publicvoid?startElement(String uri, String localName, String qName,
Attributes attributes)?throws?SAXException {
if("person".equals(localName)){
Integer id?=new?Integer(attributes.getValue(0));?//取id
person?=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
*/
@Override
publicvoid?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);
}elseif("age".equals(perTag)){
person.setAge(new?Short(data));
}
}
}
@Override
publicvoid?endElement(String uri, String localName, String qName)
throws?SAXException {
if("person".equals(localName)){
persons.add(person);
person?=null;
}
perTag?=null;
}
public?List<Person>?getPersons() {
return?persons;
}
}SAXPerson.java
import?java.io.InputStream;
import?java.util.List;
import?javax.xml.parsers.SAXParser;
import?javax.xml.parsers.SAXParserFactory;
import?com.sinber.domain.Person;
publicclass?SAXPerson{
publicstatic?List<Person>?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.java?import?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;
publicclass?DOMPerson {
publicstatic?List<Person>?getPerson()?throws?Exception{
List<Person>?pers?=new?ArrayList<Person>();
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()));
}elseif("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;
publicclass?PullPerson {
publicstaticvoid?save(List<Person>?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");?//person
serializer.attribute("",?"id",?""+person.getId());
serializer.startTag("",?"name");?//name
serializer.text(person.getName());
serializer.endTag("",?"name");?//name
serializer.startTag("",?"age");?//age
serializer.text(person.getAge().toString());
serializer.endTag("",?"age");//age
serializer.endTag("",?"person");?//person
}
serializer.endTag("",?"persons");
serializer.endDocument();
outStream.close();
}
publicstatic?List<Person>?getPersons()?throws?Exception{
List<Person>?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<Person>();
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)));
}elseif(person!=null){
if("name".equals(parser.getName())){
person.setName(parser.nextText());
}elseif("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。?9.根据自己的理解描述下Android数字签名。?答：(1)所有的应用程序都必须有数字证书，Android系统不会安装一个没有数字证书的应用程序
(2)Android程序包使用的数字证书可以是自签名的，不需要一个权威的数字证书机构签名认证
(3)如果要正式发布一个Android ，必须使用一个合适的私钥生成的数字证书来给程序签名，而不能使用adt插件或者ant工具生成的调试证书来发布。
(4)数字证书都是有有效期的，Android只是在应用程序安装的时候才会检查证书的有效期。如果程序已经安装在系统中，即使证书过期也不会影响程序的正常功能。??10.已知单链表的头结构head,写一个函数把这个链表逆序。答：?如下所示Node.javapublicclass?Node {
private?Integer count;
private?Node nextNode;
public?Node(){
}
public?Node(int?count){
this.count?=new?Integer(count);
}
public?Integer getCount() {
return?count;
}
publicvoid?setCount(Integer count) {
this.count?=?count;
}
public?Node getNextNode() {
return?nextNode;
}
publicvoid?setNextNode(Node nextNode) {
this.nextNode?=?nextNode;
}
}ReverseSingleLink.javapublicclass?ReverseSingleLink {
publicstatic?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;?
}
publicstaticvoid?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();
}
}
}
