java笔试面试题目

1、l JBS1.列举出 10个JAVA语言的优势a:免费，开源，跨平台(平台独立性)，简单易用，功能完善，面向对象，健壮性，多线程，结构中立，企业应用的成熟平台, 无线应用2.列举出JAVA中10个面向对象编程的术语a:包，类，接口，对象，属性，方法，构造器，继承，封装，多态，抽象，范型3.列举出JAVA中6个比较常用的包Java.lang;java.util;java.io;java.sql;java.awt;java.applet;javax.swing4.JAVA中的标识符有什么作用和特点作用：标识符用作给变量、类和方法命名特点：可以以字母、下划线“_”和”$”符开头首字符外，可以跟上字母

2、、下划线“_”和”$”符或数字Java是大小写敏感的，标识符也不例外5.JAVA中的关键字有什么特点,列举出至少20个关键字Java中一些赋以特定的含义、并用做专门用途的单词称为关键字（keyword） 所有Java关键字都是小写的，TURE、FALSE、NULL等都不是Java关键字 ； goto和const 虽然从未被使用，但也作为Java关键字保留； 中一共有51个关键字Javaabstract assert boolean break byte continue case catch char class const double default do extends else fin

3、al float for goto long if implements import native new null instanceof int interface package private protected public return short static strictfp super switch synchronized this while void throw throws transient try volatile 6.JAVA中数据类型如何分类？ 可分为简单数据类型和引用数据类型:简单数据类型：数值型（byte,short,int,long,float doub

4、le)，字符型(char)，布尔型(boolean);引用数据类型：类，接口，数组.7.JAVA中运算符的分类及举例 分割符：,，;，() 算术运算符: +，*，/，%，+， 关系运算符: >，<，>=，<=，=，!= 布尔逻辑运算符: !，& , | , , &&，| 位运算符: &，|， ， >>，<<，>>> 赋值运算符: = 扩展赋值运算符:+=，=，*=，/= 字符串连接运算符: + 造型操作符：() 8.super,this关键字的作用及用法 在Java类中使用super来引用父类的成

5、分 可用于访问父类中定义的属性super 可用于调用父类中定义的成员方法super 可用于在子类构造器中调用父类的构造器super 的追溯不仅于直接父类super 中为解决变量的命名冲突和不确定性问题，引入关键字“this”代表其所在方法的当前对象。Java 构造器中指该构造器所创建的新对象 方法中指调用该方法的对象 关键字的用法this 在类本身的方法或构造器中引用该类的实例变量和方法 将当前对象作为参数传递给其它方法或构造器 用来调用其他的重载的构造器 9.什么是JAVA中的表达式？有什么作用？ 表达式是运算符和操作数的结合，它是任何一门编程语言的关键组成部分 表达式允许程序员进行数学计算

6、、值的比较、逻辑操作以及在Java中进行对象的操作。 一些表达式的例子： X X+10 Y=x+10 Arr10 student.geName() 10.做表列出JAVA中所有修饰符和他们的适用范围(能不能修饰构造器，属性，自由块等) class 属性 方法 构建器 自由块 内部类 public Y Y Y Y Y protected Y Y Y Y (Default) Y Y Y Y Y Y private Y Y Y Y final Y Y Y Y abstract Y Y Y static Y Y Y 11.写一个方法，用一个for循环打印九九乘法表 /* *一个for循环打印九九乘法表

7、 */ publicvoid nineNineMultiTable() for (int i = 1,j = 1; j <= 9; i+) System.out.print(i+"*"+j+"="+i*j+" "); if(i=j) i=0; j+; System.out.println(); 12.给定一个java.util.Date对象，如何转化为”2007-3-22 20:23:22”格式的字符串/* *将某个日期以固定格式转化成字符串 *paramdate *returnstr */ public String date

8、ToStr(java.util.Date date) SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); String str = sdf.format(date); return str; 13.写一个方法，能够判断任意一个整数是否素数/* *判断任意一个整数是否素数 *paramn *returnboolean */ publicboolean isPrimes(int n) for (int i = 2; i <= Math.sqrt(n); i+) if(n%i=0) retu

9、rnfalse; returntrue; 14.写一个方法，输入任意一个整数，返回它的阶乘/* *获得任意一个整数的阶乘 *paramn *returnn! */ publicint factorial(int n) /递归 if(n=1) return 1; return n*factorial(n-1); /非递归/ int multi = 1;/ for (int i = 2; i <= n; i+) / multi*=i;/ / return multi; 15.写一个方法，用二分查找法判断任意整数在任意整数数组里面是否存在，若存在就返回它在数组中的索引位置，不存在返回-1/*

10、*二分查找特定整数在整型数组中的位置(递归) *paramdataset *paramdata *parambeginIndex *paramendIndex *returnindex */ publicint binarySearch(int dataset,int data,int beginIndex,int endIndex) int midIndex = (beginIndex+endIndex)/2; if(data<datasetbeginIndex|data>datasetendIndex|beginIndex>endIndex)return -1; if(d

11、ata<datasetmidIndex) return binarySearch(dataset,data,beginIndex,midIndex-1); elseif(data>datasetmidIndex) return binarySearch(dataset,data,midIndex+1,endIndex); else return midIndex; /* *二分查找特定整数在整型数组中的位置(非递归) *paramdataset *paramdata *returnindex */ publicint binarySearch(int dataset ,int da

12、ta) int beginIndex = 0; int endIndex = dataset.length - 1; int midIndex = -1; if(data<datasetbeginIndex|data>datasetendIndex|beginIndex>endIndex)return -1; while(beginIndex <= endIndex) midIndex = (beginIndex+endIndex)/2; if(data<datasetmidIndex) endIndex = midIndex-1; elseif(data>

13、datasetmidIndex) beginIndex = midIndex+1; else return midIndex; return -1; 16.做一个饲养员给动物喂食物的例子体现JAVA中的面向对象思想,接口（抽象类）的用处package com.softeem.demo; /* *authorleno *动物的接口 */interface Animal publicvoid eat(Food food);/* *authorleno *一种动物类:猫 */class Cat implements Animal publicvoid eat(Food food) System.ou

14、t.println("小猫吃"+food.getName(); /* *authorleno *一种动物类:狗 */class Dog implements Animal publicvoid eat(Food food) System.out.println("小狗啃"+food.getName(); /* *authorleno *食物抽象类 */abstractclass Food protected String name; public String getName() returnname; publicvoid setName(String

15、 name) = name; /* *authorleno *一种食物类:鱼 */class Fish extends Food public Fish(String name) = name; /* *authorleno *一种食物类:骨头 */class Bone extends Food public Bone(String name) = name; /* *authorleno *饲养员类 * */class Feeder /* *饲养员给某种动物喂某种食物 *paramanimal *paramfood */ publi

16、cvoid feed(Animal animal,Food food) animal.eat(food); /* *authorleno *测试饲养员给动物喂食物 */publicclass TestFeeder publicstaticvoid main(String args) Feeder feeder=new Feeder(); Animal animal=new Dog(); Food food=new Bone("肉骨头"); feeder.feed(animal,food); /给狗喂肉骨头 animal=new Cat(); food=new Fish(&q

17、uot;鱼"); feeder.feed(animal,food); /给猫喂鱼 17.描述JAVA中异常处理的机制 程序的执行过程中如出现异常，会自动生成一个异常类对象，该异常对象将被提交给Java运行时系统，这个过程称为抛出(throw)异常。Java 当Java运行时系统接收到异常对象时，会寻找能处理这一异常的代码并把当前异常对象交给其处理，这一过程称为捕获(catch)异常。 如果Java运行时系统找不到可以捕获异常的方法，则运行时系统将终止，相应的Java程序也将退出。 程序员通常只能处理违例(Exception)，而对错误(Error)无能为力。 18. 做一个单子模式的

18、类，只加载一次属性文件package com.softeem.demo; import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStream;import java.util.Properties; /* *authorleno *单子模式，保证在整个应用期间只加载一次配置属性文件 */publicclass Singleton privatestatic Singleton instance; privatestati

19、cfinal String CONFIG_FILE_PATH = "E:perties" private Properties config; private Singleton() config = new Properties(); InputStream is; try is = new FileInputStream(CONFIG_FILE_PATH); config.load(is); is.close(); catch (FileNotFoundException e) / TODO Auto-generated catch block e.

20、printStackTrace(); catch (IOException e) / TODO Auto-generated catch block e.printStackTrace(); publicstatic Singleton getInstance() if(instance=null) instance = new Singleton(); returninstance; public Properties getConfig() returnconfig; publicvoid setConfig(Properties config) this.config = config;

21、 l J2SE19.拷贝一个目录(文件)到指定路径/* *拷贝一个目录或者文件到指定路径下 *paramsource *paramtarget */ publicvoid copy(File source,File target) File tarpath = new File(target,source.getName(); if(source.isDirectory() tarpath.mkdir(); File dir = source.listFiles(); for (int i = 0; i < dir.length; i+) copy(diri,tarpath); else

22、 try InputStream is = new FileInputStream(source); OutputStream os = new FileOutputStream(tarpath); byte buf = newbyte1024; int len = 0; while(len = is.read(buf)!=-1) os.write(buf,0,len); is.close(); os.close(); catch (FileNotFoundException e) / TODO Auto-generated catch block e.printStackTrace(); c

23、atch (IOException e) / TODO Auto-generated catch block e.printStackTrace(); 20.用JAVA中的多线程示例银行取款问题packagecom.softeem.demo; /* *authorleno *账户类 *默认有余额，可以取款 */class Account privatefloatbalance = 1000; publicfloat getBalance() returnbalance; publicvoid setBalance(float balance) this.balance = balance; /

24、* *取款的方法需要同步 *parammoney */ publicsynchronizedvoid withdrawals(float money) if(balance>=money) System.out.println("被取走"+money+"元!"); try Thread.sleep(1000); catch (InterruptedException e) / TODO Auto-generated catch block e.printStackTrace(); balance-=money; else System.out.pr

25、intln("对不起,余额不足!"); /* *authorleno *银行卡 */class TestAccount1 extends Thread private Account account; public TestAccount1(Account account) this.account = account; Override publicvoid run() account.withdrawals(800); System.out.println("余额为:"+account.getBalance()+"元!"); /*

26、 *authorleno *存折 */ class TestAccount2 extends Thread private Account account; public TestAccount2(Account account) this.account = account; Override publicvoid run() account.withdrawals(700); System.out.println("余额为:"+account.getBalance()+"元!"); publicclass Test publicstaticvoid

27、main(String args) Account account = new Account(); TestAccount1 testAccount1 = new TestAccount1(account); testAccount1.start(); TestAccount2 testAccount2 = new TestAccount2(account); testAccount2.start(); 21.用JAVA中的多线程示例火车站售票问题package com.softeem.demo; /* *authorleno *售票类 */class SaleTicket implemen

28、ts Runnable inttickets = 100; publicvoid run() while (tickets > 0) sale();/或者下面这样实现/ synchronized (this) / if (tickets > 0) / System.out.println(Thread.currentThread().getName() + "卖第"/ + (100 - tickets + 1) + "张票");/ tickets-;/ / publicsynchronizedvoid sale() if (tickets &

29、gt; 0) System.out.println(Thread.currentThread().getName() + "卖第" + (100 - tickets + 1) + "张票"); tickets-; publicclass TestSaleTicket publicstaticvoid main(String args) SaleTicket st = new SaleTicket(); new Thread(st, "一号窗口").start(); new Thread(st, "二号窗口").st

30、art(); new Thread(st, "三号窗口").start(); new Thread(st, "四号窗口").start(); 22.用JAVA中的多线程示例生产者和消费者问题package com.softeem.demo; class Producer implements Runnableprivate SyncStack stack; public Producer(SyncStack stack) this.stack = stack; publicvoid run() for (int i = 0; i < stack.g

31、etProducts().length; i+) String product = "产品"+i; stack.push(product); System.out.println("生产了: "+product); try Thread.sleep(200); catch(InterruptedException e) e.printStackTrace(); class Consumer implements Runnable private SyncStack stack; public Consumer(SyncStack stack) this.

32、stack = stack; publicvoid run() for(int i=0;i<stack.getProducts().length;i+) String product =stack.pop(); System.out.println("消费了: "+product); try Thread.sleep(1000); catch(InterruptedException e) e.printStackTrace(); class SyncStack private String products = new String10; privateintind

33、ex; publicsynchronizedvoid push(String product) if(index=product.length() try wait(); catch (InterruptedException e) / TODO Auto-generated catch block e.printStackTrace(); notify(); productsindex=product; index+; publicsynchronized String pop() if(index=0) try wait(); catch (InterruptedException e)

34、/ TODO Auto-generated catch block e.printStackTrace(); notify(); index-; String product = productsindex; return product; public String getProducts() returnproducts; publicclass TestProducerConsumer publicstaticvoid main(String args) SyncStack stack=new SyncStack(); Producer p=new Producer(stack); Co

35、nsumer c=new Consumer(stack); new Thread(p).start(); new Thread(c).start(); 19. 23.编程实现序列化的Student（sno,sname）对象在网络上的传输package com.softeem.demo; import java.io.IOException;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;import java.io.Serializable;import .ServerSocket;import .Socke

36、t; class Student implements Serializable private int sno; private String sname; public Student(int sno, String sname) this.sno = sno; this.sname = sname; public int getSno() return sno; public void setSno(int sno) this.sno = sno; public String getSname() return sname; public void setSname(String sna

37、me) this.sname = sname; Override public String toString() return "学号:" + sno + "姓名:" + sname; class MyClient extends Thread Override public void run() try Socket s = new Socket("localhost", 9999); ObjectInputStream ois = new ObjectInputStream(s.getInputStream(); Student

38、 stu = (Student) ois.readObject(); System.out.println("客户端程序收到服务器端程序传输过来的学生对象>> " + stu); ois.close(); s.close(); catch (IOException e) / TODO Auto-generated catch block e.printStackTrace(); catch (ClassNotFoundException e) / TODO Auto-generated catch block e.printStackTrace(); class

39、 MyServer extends Thread Override public void run() try ServerSocket ss = new ServerSocket(9999); Socket s = ss.accept(); ObjectOutputStream ops = new ObjectOutputStream(s.getOutputStream(); Student stu = new Student(1, "赵本山"); ops.writeObject(stu); ops.close(); s.close(); ss.close(); catc

40、h (IOException e) / TODO Auto-generated catch block e.printStackTrace(); public class TestTransfer public static void main(String args) new MyServer().start(); new MyClient().start(); l JDBC24.用dom4j组件解析如下XML格式的文件：<?xml version="1.0" encoding="UTF-8"?><generator><t

41、able name="login" operation="1"> <column name="username" handle="0">aaa</column> <column name="password" handle="0">123</column></table><table name="login" operation="2"> <column

42、 name="id" handle="1">1</column> <column name="username" handle="0">bbb</column> <column name="password" handle="0">444</column></table><table name="login" operation="3"> <

43、column name="id" handle="1">4</column></table></generator>规则：<table>operation 1表insert,2表update，3表delete.<column>handle 1表作为where条件,0表作为操作字段。要求：按照规则生成三条SQL语句！(即做一个方法解析xml文件生成一个含有三条SQL语句的字符串)/* *解析XML文件生成一个含有可执行SQL语句的字符串 *paramxmlFileName *returnSQ

44、L */ public String parseXmltoSQL(String xmlFileName) StringBuffer sbsql = new StringBuffer(); SAXReader reader = new SAXReader(); try Document document = reader.read(new File(xmlFileName); Element element = document.getRootElement(); Iterator it = element.elementIterator("table"); while (i

45、t.hasNext() element = (Element) it.next(); /获得对表的操作 String oper = element.attributeValue("operation"); /获得表名 String tableName = element.attributeValue("name"); if ("1".equals(oper) sbsql.append("insert into ").append(tableName); Iterator it2 = element.elementI

46、terator("column"); String columnName1 = null; String columnValue1 = null; String columnName2 = null; String columnValue2 = null; if (it2.hasNext() element = (Element) it2.next(); columnName1 = element.attributeValue("name"); columnValue1 = element.getText(); if (it2.hasNext() ele

47、ment = (Element) it2.next(); columnName2 = element.attributeValue("name"); columnValue2 = element.getText(); sbsql.append("("+columnName1+","+columnName2+")"+" values('"+columnValue1+"','"+columnValue2+"')n"); else

48、if ("2".equals(oper) sbsql.append("update ").append(tableName); Iterator it2 = element.elementIterator("column"); String columnName1 = null; String columnValue1 = null; String columnName2 = null; String columnValue2 = null; String columnName3 = null; String columnValue3

49、 = null; if (it2.hasNext() element = (Element) it2.next(); columnName1 = element.attributeValue("name"); columnValue1 = element.getText(); if (it2.hasNext() element = (Element) it2.next(); columnName2 = element.attributeValue("name"); columnValue2 = element.getText(); if (it2.hasNext() eleme