Android笔试小结

Android笔试总结

?> <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

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.java

import 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<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    public void startDocument() throws SAXException {        persons = new ArrayList<Person>();    }    @Override    public void 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    public 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));            }        }    }    @Override    public void 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;public class SAXPerson{    public static 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;public class DOMPerson {    public static 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()));                    }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.java

import 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<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();    }    public static 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)));                }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。?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.java

public 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.java

public 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();        }    }}

查看更多 下一篇