java初级面试题（二）

我不是女神ヾ 2024-02-17 15:44 55阅读 0赞

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  
\*/  
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 dateToStr(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)  
\{  
returnfalse;  
\}  
\}  
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  
/\*\*  
\*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 <dataset\[beginIndex\]||data>dataset\[endIndex\]||beginIndex>endIndex)return -1;  
if(data <dataset\[midIndex\])  
\{  
return binarySearch(dataset,data,beginIndex,midIndex-1);  
\}elseif(data>dataset\[midIndex\])  
\{  
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 data)  
\{  
int beginIndex = 0;  
int endIndex = dataset.length - 1;  
int midIndex = -1;  
if(data <dataset\[beginIndex\]||data>dataset\[endIndex\]||beginIndex>endIndex)return -1;  
while(beginIndex <= endIndex) \{  
midIndex = (beginIndex+endIndex)/2;  
if(data <dataset\[midIndex\]) \{  
endIndex = midIndex-1;  
\} elseif(data>dataset\[midIndex\]) \{  
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.out.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 name) \{  
this.name = name;  
\}  
\}  
  
/\*\*  
\*@authorleno  
\*一种食物类:鱼  
\*/  
class Fish extends Food  
\{  
public Fish(String name) \{  
this.name = name;  
\}  
\}  
/\*\*  
\*@authorleno  
\*一种食物类:骨头  
\*/  
class Bone extends Food  
\{  
public Bone(String name) \{  
this.name = name;  
\}  
\}  
  
/\*\*  
\*@authorleno  
\*饲养员类  
\*  
\*/  
class Feeder  
\{  
/\*\*  
\*饲养员给某种动物喂某种食物  
\*@paramanimal  
\*@paramfood  
\*/  
publicvoid 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("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;  
privatestaticfinal String CONFIG\_FILE\_PATH = "E:\\\\config.properties";  
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.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;  
\}  
  
  
  
\}  
l J2SE  
19.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(dir\[i\],tarpath);  
\}  
\}else  
\{  
try \{  
InputStream is = new FileInputStream(source);  
OutputStream os = new FileOutputStream(tarpath);  
byte\[\] buf = newbyte\[1024\];  
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();  
\} catch (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;  
\}  
  
/\*\*  
\*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.println("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!");  
\}  
\}  
/\*\*  
\*@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 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 implements 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 > 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").start();  
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 Runnable  
\{  
private SyncStack stack;  
  
public Producer(SyncStack stack) \{  
this.stack = stack;  
\}  
  
publicvoid run() \{  
for (int i = 0; i < stack.getProducts().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.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 String\[10\];  
privateintindex;  
publicsynchronizedvoid push(String product)  
\{  
if(index==product.length())  
\{  
try \{  
wait();  
\} catch (InterruptedException e) \{  
// TODO Auto-generated catch block  
e.printStackTrace();  
\}  
\}  
notify();  
products\[index\]=product;  
index++;  
\}  
  
publicsynchronized String pop()  
\{  
if(index==0)  
\{  
try \{  
wait();  
\} catch (InterruptedException e) \{  
// TODO Auto-generated catch block  
e.printStackTrace();  
\}  
\}  
notify();  
index--;  
String product = products\[index\];  
return product;  
\}  
  
public String\[\] getProducts() \{  
returnproducts;  
\}  
  
  
\}  
publicclass TestProducerConsumer \{  
  
publicstaticvoid main(String\[\] args) \{  
SyncStack stack=new SyncStack();  
Producer p=new Producer(stack);  
Consumer c=new Consumer(stack);  
  
new Thread(p).start();  
new Thread(c).start();  
\}  
\}