java代码与编程题(经典)

代码与编程题

135、写一个Singleton出来

Singleton模式主要作用是保证在Java应用程序中，一个类Class只有一个实例存在。

一般Singleton模式通常有几种种形式:

第一种形式: 定义一个类，它的构造函数为private的，它有一个static的private的该类变量，在类初始化时实例话，通过一个public的getInstance方法获取对它的引用,继而调用其中的方法。

public class Singleton {

private Singleton(){}

//在自己内部定义自己一个实例，是不是很奇怪？

//注意这是private 只供内部调用

private static Singleton instance = new Singleton();

//这里提供了一个供外部访问本class的静态方法，可以直接访问

public static Singleton getInstance() {

return instance;

}

}

第二种形式:

public class Singleton {

private static Singleton instance = null;

public static synchronized Singleton getInstance() {

//这个方法比上面有所改进，不用每次都进行生成对象，只是第一次

//使用时生成实例，提高了效率！

if (instance==null)

instance＝new Singleton();

return instance; }

}

其他形式:

定义一个类，它的构造函数为private的，所有方法为static的。

一般认为第一种形式要更加安全些

136、继承时候类的执行顺序问题,一般都是选择题,问你将会打印出什么?

答:父类：

package test;

public class FatherClass

{

public FatherClass()

{

System.out.println(\"FatherClass Create\");

}

}

子类:

package test;

import test.FatherClass;

public class ChildClass extends FatherClass

{

public ChildClass()

{

System.out.println(\"ChildClass Create\");

}

public static void main(String[] args)

{

FatherClass fc = new FatherClass();

ChildClass cc = new ChildClass();

}

}

输出结果：

C:\\>java test.ChildClass

FatherClass Create

FatherClass Create

ChildClass Create

137、内部类的实现方式?

答：示例代码如下：

package test;

public class OuterClass

{

private class InterClass

{

public InterClass()

{

System.out.println(\"InterClass Create\");

}

}

public OuterClass()

{

InterClass ic = new InterClass();

System.out.println(\"OuterClass Create\");

}

public static void main(String[] args)

{

OuterClass oc = new OuterClass();

}

}

输出结果:

C:\\>java test/OuterClass

InterClass Create

OuterClass Create

再一个例题：

public class OuterClass {

private double d1 = 1.0;

//insert code here

}

You need to insert an inner class declaration at line 3. Which two inner class declarations are

valid?(Choose two.)

A. class InnerOne{

public static double methoda() {return d1;}

}

B. public class InnerOne{

static double methoda() {return d1;}

}

C. private class InnerOne{

double methoda() {return d1;}

}

D. static class InnerOne{

protected double methoda() {return d1;}

}

E. abstract class InnerOne{

public abstract double methoda();

}

说明如下：

一.静态内部类可以有静态成员，而非静态内部类则不能有静态成员。 故 A、B 错

二.静态内部类的非静态成员可以访问外部类的静态变量，而不可访问外部类的非静态变量；return d1 出错。

故 D 错

三.非静态内部类的非静态成员可以访问外部类的非静态变量。 故 C 正确

四.答案为C、E

138、Java 的通信编程，编程题(或问答)，用JAVA SOCKET编程，读服务器几个字符，再写入本地显示？

答:Server端程序:

package test;

import java.net.*;

import java.io.*;

public class Server

{

private ServerSocket ss;

private Socket socket;

private BufferedReader in;

private PrintWriter out;

public Server()

{

try

{

ss=new ServerSocket(10000);

while(true)

{

socket = ss.accept();

String RemoteIP = socket.getInetAddress().getHostAddress();

String RemotePort = \":\"+socket.getLocalPort();

System.out.println(\"A client come in!IP:\"+RemoteIP+RemotePort);

in = new BufferedReader(new

InputStreamReader(socket.getInputStream()));

String line = in.readLine();

System.out.println(\"Cleint send is :\" + line);

out = new PrintWriter(socket.getOutputStream(),true);

out.println(\"Your Message Received!\");

out.close();

in.close();

socket.close();

}

}catch (IOException e)

{

out.println(\"wrong\");

}

}

public static void main(String[] args)

{

new Server();

}

};

Client端程序:

package test;

import java.io.*;

import java.net.*;

public class Client

{

Socket socket;

BufferedReader in;

PrintWriter out;

public Client()

{

try

{

System.out.println(\"Try to Connect to 127.0.0.1:10000\");

socket = new Socket(\"127.0.0.1\

System.out.println(\"The Server Connected!\");

System.out.println(\"Please enter some Character:\");

BufferedReader line = new BufferedReader(new

InputStreamReader(System.in));

out = new PrintWriter(socket.getOutputStream(),true);

out.println(line.readLine());

in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

System.out.println(in.readLine());

out.close();

in.close();

socket.close();

}catch(IOException e)

{

out.println(\"Wrong\");

}

}

public static void main(String[] args)

{

new Client();

}

};

139、用JAVA实现一种排序，JAVA类实现序列化的方法(二种)？ON框架中，实现比较要实现什么样的接口？

答:用插入法进行排序代码如下

package test;

import java.util.*;

class InsertSort

{

ArrayList al;

public InsertSort(int num,int mod)

{

如在COLLECTI

al = new ArrayList(num);

Random rand = new Random();

System.out.println(\"The ArrayList Sort Before:\");

for (int i=0;i{

al.add(new Integer(Math.abs(rand.nextInt()) % mod + 1));

System.out.println(\"al[\"+i+\"]=\"+al.get(i));

}

}

public void SortIt()

{

Integer tempInt;

int MaxSize=1;

for(int i=1;i{

tempInt = (Integer)al.remove(i);

if(tempInt.intValue()>=((Integer)al.get(MaxSize-1)).intValue())

{

al.add(MaxSize,tempInt);

MaxSize++;

System.out.println(al.toString());

} else {

for (int j=0;j{

if

(((Integer)al.get(j)).intValue()>=tempInt.intValue())

{

al.add(j,tempInt);

MaxSize++;

System.out.println(al.toString());

break;

}

}

}

}

System.out.println(\"The ArrayList Sort After:\");

for(int i=0;i{

System.out.println(\"al[\"+i+\"]=\"+al.get(i));

}

}

public static void main(String[] args)

{

InsertSort is = new InsertSort(10,100);

is.SortIt();

}

}

140、编程：编写一个截取字符串的函数，输入为一个字符串和字节数，输出为按字

节截取的字符串。 但是要保证汉字不被截半个，如“我ABC”4，应该截为“我AB”，输入“我ABC汉DEF”，6，应该输出为“我ABC”而不是“我ABC+汉的半个”。

答：代码如下：

package test;

class SplitString

{

String SplitStr;

int SplitByte;

public SplitString(String str,int bytes)

{

SplitStr=str;

SplitByte=bytes;

System.out.println(\"The String is:'\"+SplitStr+\"';SplitBytes=\"+SplitByte);

}

public void SplitIt()

{

int loopCount;

loopCount=(SplitStr.length()%SplitByte==0)?(SplitStr.length()/SplitByte):(SplitStr.length()/Split

Byte+1);

System.out.println(\"Will Split into \"+loopCount);

for (int i=1;i<=loopCount ;i++ )

{

if (i==loopCount){

System.out.println(SplitStr.substring((i-1)*SplitByte,SplitStr.length()));

} else {

System.out.println(SplitStr.substring((i-1)*SplitByte,(i*SplitByte)));

}

}

}

public static void main(String[] args)

{

SplitString ss = new SplitString(\"test中dd文dsaf中男大3443n中国43中国人

0ewldfls=103\

ss.SplitIt();

}

}

141、JAVA多线程编程。 用JAVA写一个多线程程序，如写四个线程，二个加1，二个对一个变量减一，输出。

希望大家补上，谢谢

142、可能会让你写一段Jdbc连Oracle的程序,并实现数据查询.

答:程序如下：

package hello.ant;

import java.sql.*;

public class jdbc

{

String dbUrl=\"jdbc:oracle:thin:@127.0.0.1:1521:orcl\";

String theUser=\"admin\";

String thePw=\"manager\";

Connection c=null;

Statement conn;

ResultSet rs=null;

public jdbc()

{

try{

Class.forName(\"oracle.jdbc.driver.OracleDriver\").newInstance();

c = DriverManager.getConnection(dbUrl,theUser,thePw);

conn=c.createStatement();

}catch(Exception e){

e.printStackTrace();

}

}

public boolean executeUpdate(String sql)

{

try

{

conn.executeUpdate(sql);

return true;

}

catch (SQLException e)

{

e.printStackTrace();

return false;

}

}

public ResultSet executeQuery(String sql)

{

rs=null;

try

{

rs=conn.executeQuery(sql);

}

catch (SQLException e)

{

e.printStackTrace();

}

return rs;

}

public void close()

{

try

{

conn.close();

c.close();

}

catch (Exception e)

{

e.printStackTrace();

}

}

public static void main(String[] args)

{

ResultSet rs;

jdbc conn = new jdbc();

rs=conn.executeQuery(\"select * from test\");

try{

while (rs.next())

{

System.out.println(rs.getString(\"id\"));

System.out.println(rs.getString(\"name\"));

}

}catch(Exception e)

{

e.printStackTrace();

}

}

}

143、ORACLE大数据量下的分页解决方法。一般用截取ID方法，还有是三层嵌套方法。

答:一种分页方法

<%

int i=1;

int numPages=14;

String pages = request.getParameter(\"page\") ;

int currentPage = 1;

currentPage=(pages==null)?(1):{Integer.parseInt(pages)}

sql = \"select count(*) from tables\";

ResultSet rs = DBLink.executeQuery(sql) ;

while(rs.next()) i = rs.getInt(1) ;

int intPageCount=1;

intPageCount=(i%numPages==0)?(i/numPages):(i/numPages+1);

int nextPage ;

int upPage;

nextPage = currentPage+1;

if (nextPage>=intPageCount) nextPage=intPageCount;

upPage = currentPage-1;

if (upPage<=1) upPage=1;

rs.close();

sql=\"select * from tables\";

rs=DBLink.executeQuery(sql);

i=0;

while((i%>

//输出内容

//输出翻页连接

合计:<%=currentPage%>/<%=intPageCount%>第一页href=\"List.jsp?page=<%=upPage%>\">上一页

<%

for(int j=1;j<=intPageCount;j++){

if(currentPage!=j){

%>

\">[<%=j%>]

<%

}else{

out.println(j);

}

}

%>

\">下一页\">最后页

144、用jdom解析xml文件时如何解决中文问题?如何解析?

答:看如下代码,用编码方式加以解决

package test;

import java.io.*;

public class DOMTest

{

private String inFile = \"c:\\\\people.xml\";

private String outFile = \"c:\\\\people.xml\";

public static void main(String args[])

{

new DOMTest();

}

public DOMTest()

{

try

{

javax.xml.parsers.DocumentBuilder builder =

javax.xml.parsers.DocumentBuilderFactory.newInstance().newDocumentBuilder();

org.w3c.dom.Document doc = builder.newDocument();

org.w3c.dom.Element root = doc.createElement(\"老师\");

org.w3c.dom.Element wang = doc.createElement(\"王\");

org.w3c.dom.Element liu = doc.createElement(\"刘\");

wang.appendChild(doc.createTextNode(\"我是王老师\"));

root.appendChild(wang);

doc.appendChild(root);

javax.xml.transform.Transformer transformer =

javax.xml.transform.TransformerFactory.newInstance().newTransformer();

transformer.setOutputProperty(javax.xml.transform.OutputKeys.ENCODING, \"gb2312\");

transformer.setOutputProperty(javax.xml.transform.OutputKeys.INDENT, \"yes\");

transformer.transform(new javax.xml.transform.dom.DOMSource(doc),

new

javax.xml.transform.stream.StreamResult(outFile));

}

catch (Exception e)

{

System.out.println (e.getMessage());

}

}

}

145、编程用JAVA解析XML的方式.

答:用SAX方式解析XML，XML文件如下：

王小明

信息学院

6258113

男,1955年生,博士，95年调入海南大学

事件回调类SAXHandler.java

import java.io.*;

import java.util.Hashtable;

import org.xml.sax.*;

public class SAXHandler extends HandlerBase

{

private Hashtable table = new Hashtable();

private String currentElement = null;

private String currentValue = null;

public void setTable(Hashtable table)

{

this.table = table;

}

public Hashtable getTable()

{

return table;

}

public void startElement(String tag, AttributeList attrs)

throws SAXException

{

currentElement = tag;

}

public void characters(char[] ch, int start, int length)

throws SAXException

{

currentValue = new String(ch, start, length);

}

public void endElement(String name) throws SAXException

{

if (currentElement.equals(name))

table.put(currentElement, currentValue);

}

}

JSP内容显示源码,SaxXml.jsp:

<%@ page errorPage=\"ErrPage.jsp\"

contentType=\"text/html;charset=GB2312\" %>

<%@ page import=\"java.io.*\" %>

<%@ page import=\"java.util.Hashtable\" %>

<%@ page import=\"org.w3c.dom.*\" %>

<%@ page import=\"org.xml.sax.*\" %>

<%@ page import=\"javax.xml.parsers.SAXParserFactory\" %>

<%@ page import=\"javax.xml.parsers.SAXParser\" %>

<%@ page import=\"SAXHandler\" %>

<%

File file = new File(\"c:\\\\people.xml\");

FileReader reader = new FileReader(file);

Parser parser;

SAXParserFactory spf = SAXParserFactory.newInstance();

SAXParser sp = spf.newSAXParser();

SAXHandler handler = new SAXHandler();

sp.parse(new InputSource(reader), handler);

Hashtable hashTable = handler.getTable();

out.println(\"

out.println(\"

out.println(\"

out.println(\"

out.println(\"

out.println(\"

%>

146、EJB的基本架构

答:一个EJB包括三个部分:

Remote Interface 接口的代码

package Beans;

import javax.ejb.EJBObject;

import java.rmi.RemoteException;

public interface Add extends EJBObject

{

//some method declare

}

Home Interface 接口的代码

package Beans;

import java.rmi.RemoteException;

import jaax.ejb.CreateException;

import javax.ejb.EJBHome;

public interface AddHome extends EJBHome

{

//some method declare

}

EJB类的代码

package Beans;

import java.rmi.RemoteException;

import javax.ejb.SessionBean;

import javx.ejb.SessionContext;

public class AddBean Implements SessionBean

{

//some method declare

}

147、如何校验数字型?

var re=/^\\d{1,8}$|\\.\\d{1,2}$/;

var str=document.form1.all(i).value;

var r=str.match(re);

if (r==null)

{

sign=-4;

break;

}

else{

document.form1.all(i).value=parseFloat(str);

}

148、将一个键盘输入的数字转化成中文输出

(例如:输入:1234567 输出:一百二拾三万四千五百六拾七)

用java语言实现,,请编一段程序实现!

public class Reader {

private String strNum;

private String strNumChFormat;

private String strNumTemp;

private int intNumLen;

private String strBegin;

public Reader(String strNum) {

this.strNum = strNum;

}

public boolean check(String strNum) {

boolean valid = false;

if (strNum.substring(0,1).equals(\"0\")){

this.strNum = strNum.substring(1);

}

try {

new Double(strNum);

valid = true;

}

catch (NumberFormatException ex) {

System.out.println(\"Bad number format!\");

}

return valid;

}

public void init() {

strNumChFormat = \"\";

intNumLen = strNum.length();

strNumTemp = strNum;

strNumTemp = strNumTemp.replace('1', '一');

strNumTemp = strNumTemp.replace('2', '二');

strNumTemp = strNumTemp.replace('3', '三');

strNumTemp = strNumTemp.replace('4', '四');

strNumTemp = strNumTemp.replace('5', '五');

strNumTemp = strNumTemp.replace('6', '六');

strNumTemp = strNumTemp.replace('7', '七');

strNumTemp = strNumTemp.replace('8', '八');

strNumTemp = strNumTemp.replace('9', '九');

strNumTemp = strNumTemp.replace('0', '零');

strNumTemp = strNumTemp.replace('.', '点');

strBegin = strNumTemp.substring(0, 1);

}

public String readNum() {

if (check(strNum)) {

init();

try {

for (int i = 1, j = 1, k = 1; i < intNumLen; i++) {

if (strNumTemp.charAt(intNumLen - 1) == '零' && i == 1) {

strNumChFormat = \"位\";

}

else if (strNumTemp.charAt(intNumLen - i) == '零' && j == 1) {

strNumChFormat = \"位\" + strNumChFormat;

}

else if (strNumTemp.charAt(intNumLen - i) == '点') {

j = 1;

k = 1;

strNumChFormat = strNumTemp.charAt(intNumLen - i) + strNumChFor

mat;

continue;

}

else {

strNumChFormat = strNumTemp.charAt(intNumLen - i) + strNumChFormat;

}

if (strNumTemp.charAt(intNumLen - i - 1) != '位' &&

strNumTemp.charAt(intNumLen - i - 1) != '零') {

if (j == 1 && i < intNumLen) {

strNumChFormat = '拾' + strNumChFormat;

}

else if (j == 2 && i < intNumLen) {

strNumChFormat = '百' + strNumChFormat;

}

else if (j == 3 && i < intNumLen) {

strNumChFormat = '千' + strNumChFormat;

}

}

if (j == 4 && i < intNumLen) {

j = 0;

}

if (k == 4 && i < intNumLen) {

strNumChFormat = '万' + strNumChFormat;

}

else if (k == 8 && i < intNumLen) {

k = 0;

strNumChFormat = '亿' + strNumChFormat;

}

j++;

k++;

}

while (strNumChFormat.indexOf(\"位\") != -1) {

strNumChFormat = strNumChFormat.replaceAll(\"位\

}

if (strNumChFormat.substring(0, 2) == \"一拾\") {

strNumChFormat = strNumChFormat.substring(1, strNumChFormat.length());

}

if (strNumChFormat.indexOf(\"点\") >= 0) {

String rebegin = strNumChFormat.substring(0,

strNumChFormat.indexOf(\"点\"));

String relast = strNumChFormat.substring(strNumChFormat.indexOf(\"点\"),

strNumChFormat.length());

for (int i = 1; i <= relast.length(); i++) {

relast = relast.replaceAll(\"拾\

relast = relast.replaceAll(\"百\

relast = relast.replaceAll(\"千\

relast = relast.replaceAll(\"万\

relast = relast.replaceAll(\"亿\

}

strNumChFormat = rebegin + relast;

}

}

catch (ArrayIndexOutOfBoundsException ex) {

ex.printStackTrace();

}

catch (Exception ex) {

ex.printStackTrace();

}

int off = strNumChFormat.indexOf(\"点\");

strNumChFormat = strBegin + strNumChFormat.substring(0);

}

else {

strNumChFormat = \"\";

}

return strNumChFormat;

}

public static void main(String args[]) {

try {

String number = args[0].toString();

System.out.println(\"The number is: \" + number);

Reader reader = new Reader(number);

System.out.println(\"Output String: \" + reader.readNum());

}

catch (Exception ex) {

System.out.println(\"Please input like that: javac Reader \");

}

}

}

149、JAVA代码查错

1.

abstract class Name {

private String name;

public abstract boolean isStupidName(String name) {}

}

大侠们，这有何错误?

答案: 错。abstract method必须以分号结尾，且不带花括号。

2.

public class Something {

void doSomething () {

private String s = \"\";

int l = s.length();

}

}

有错吗?

答案: 错。局部变量前不能放置任何访问修饰符 (private，public，和protected)。final可以用来修饰局部变量

(final如同abstract和strictfp，都是非访问修饰符，strictfp只能修饰class和method而非variable)。

3.

abstract class Something {

private abstract String doSomething ();

}

这好像没什么错吧?

答案: 错。abstract的methods不能以private修饰。abstract的methods就是让子类implement(实现)具体细节的，怎么可以用private把abstract

method封锁起来呢? (同理，abstract method前不能加final)。

4.

public class Something {

public int addOne(final int x) {

return ++x;

}

}

这个比较明显。

答案: 错。int x被修饰成final，意味着x不能在addOne method中被修改。

5.

public class Something {

public static void main(String[] args) {

Other o = new Other();

new Something().addOne(o);

}

public void addOne(final Other o) {

o.i++;

}

}

class Other {

public int i;

}

和上面的很相似，都是关于final的问题，这有错吗?

答案: 正确。在addOne method中，参数o被修饰成final。如果在addOne method里我们修改了o的reference

(比如: o = new Other();)，那么如同上例这题也是错的。但这里修改的是o的member vairable

(成员变量)，而o的reference并没有改变。

6.

class Something {

int i;

public void doSomething() {

System.out.println(\"i = \" + i);

}

}

有什么错呢? 看不出来啊。

答案: 正确。输出的是\"i = 0\"。int i属於instant variable (实例变量，或叫成员变量)。instant variable有default value。int的default value是0。

7.

class Something {

final int i;

public void doSomething() {

System.out.println(\"i = \" + i);

}

}

和上面一题只有一个地方不同，就是多了一个final。这难道就错了吗?

答案: 错。final int i是个final的instant variable (实例变量，或叫成员变量)。final的instant variable没有default value，必须在constructor (构造器)结束之前被赋予一个明确的值。可以修改为\"final int i = 0;\"。

8.

public class Something {

public static void main(String[] args) {

Something s = new Something();

System.out.println(\"s.doSomething() returns \" + doSomething());

}

public String doSomething() {

return \"Do something ...\";

}

}

看上去很完美。

答案: 错。看上去在main里call doSomething没有什么问题，毕竟两个methods都在同一个class里。但仔细看，main是static的。static method不能直接call non-static methods。可改成\"System.out.println(\"s.doSomething() returns \" + s.doSomething());\"。同理，static method不能访问non-static instant variable。

9.

此处，Something类的文件名叫OtherThing.java

class Something {

private static void main(String[] something_to_do) {

System.out.println(\"Do something ...\");

}

}

这个好像很明显。

答案: 正确。从来没有人说过Java的Class名字必须和其文件名相同。但public class的名字必须和文件名相同。

10．

interface A{

int x = 0;

}

class B{

int x =1;

}

class C extends B implements A {

public void pX(){

System.out.println(x);

}

public static void main(String[] args) {

new C().pX();

}

}

答案：错误。在编译时会发生错误(错误描述不同的JVM有不同的信息，意思就是未明确的x调用，两个x都匹配（就象在同时import java.util和java.sql两个包时直接声明Date一样）。对于父类的变量,可以用super.x来明确，而接口的属性默认隐含为 public static final.所以可以通过A.x来明确。

11.

interface Playable {

void play();

}

interface Bounceable {

void play();

}

interface Rollable extends Playable, Bounceable {

Ball ball = new Ball(\"PingPang\");

}

class Ball implements Rollable {

private String name;

public String getName() {

return name;

}

public Ball(String name) {

this.name = name;

}

public void play() {

ball = new Ball(\"Football\");

System.out.println(ball.getName());

}

}

这个错误不容易发现。

答案: 错。\"interface Rollable extends Playable, Bounceable\"没有问题。interface可继承多个interfaces，所以这里没错。问题出在interface Rollable里的\"Ball ball = new Ball(\"PingPang\");\"。任何在interface里声明的interface variable (接口变量，也可称成员变量)，默认为public static final。也就是说\"Ball ball = new Ball(\"PingPang\");\"实际上是\"public static final Ball ball = new Ball(\"PingPang\");\"。在Ball类的Play()方法中，\"ball = new Ball(\"Football\");\"改变了ball的reference，而这里的ball来自Rollable interface，Rollable interface里的ball是public static final的，final的object是不能被改变reference的。因此编译器将在\"ball = new Ball(\"Football\");\"这里显示有错。

28、设计4个线程，其中两个线程每次对j增加1，另外两个线程对j每次减少1。写出程序。

以下程序使用内部类实现线程，对j增减的时候没有考虑顺序问题。

public class ThreadTest1{

private int j;

public static void main(String args[]){

ThreadTest1 tt=new ThreadTest1();

Inc inc=tt.new Inc();

Dec dec=tt.new Dec();

for(int i=0;i<2;i++){

Thread t=new Thread(inc);

t.start();

t=new Thread(dec);

t.start();

}

}

private synchronized void inc(){

j++;

System.out.println(Thread.currentThread().getName()+\"-inc:\"+j);

}

private synchronized void dec(){

j--;

System.out.println(Thread.currentThread().getName()+\"-dec:\"+j);

}

class Inc implements Runnable{

public void run(){

for(int i=0;i<100;i++){

inc();

}

}

}

class Dec implements Runnable{

public void run(){

for(int i=0;i<100;i++){

dec();

}

}

}

}