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MySQL的最大連接數(shù)默認(rèn)是100
客戶端登錄：mysql -uusername -ppassword
設(shè)置新的最大連接數(shù)為200：mysql> set GLOBAL max_connections=200
顯示當(dāng)前運(yùn)行的Query：mysql> show processlist
顯示當(dāng)前狀態(tài)：mysql> show status
退出客戶端：mysql> exit
查看當(dāng)前最大連接數(shù)：mysqladmin -uusername -ppassword variables |find "max_con"
http://java.e800.com.cn/articles/2007/417/1176746498587392322_1.html
http://www.oracle.com/technology/tech/java/spring/how-to-jta-spring.html
When your not sure consult the 'Bible', 'Java™ Language Specification'
http://java.sun.com/docs/books/jls/t...ses.html#78119
8.3.1.3 transient Fields
Variables may be marked transient to indicate that they are not part of
the persistent state of an object.
If an instance of the class Point:
class Point {
int x, y;
transient float rho, theta;
}
were saved to persistent storage by a system service, then only the
fields x and y would be saved. This specification does not specify
details of such services; see the specification of java.io.Serializable
for an example of such a service.
8.3.1.4 volatile Fields
As described in §17, the Java programming language allows threads to
access shared variables. As a rule, to ensure that shared variables are
consistently and reliably updated, a thread should ensure that it has
exclusive use of such variables by obtaining a lock that,
conventionally, enforces mutual exclusion for those shared variables.
The Java programming language provides a second mechanism, volatile
fields, that is more convenient than locking for some purposes.
A field may be declared volatile, in which case the Java memory model
(§17) ensures that all threads see a consistent value for the variable.
If, in the following example, one thread repeatedly calls the method one
(but no more than Integer.MAX_VALUE times in all), and another thread
repeatedly calls the method two:
class Test {
static int i = 0, j = 0;
static void one() { i++; j++; }
static void two() {
System.out.println("i=" + i + " j=" + j);
}
}
then method two could occasionally print a value for j that is greater
than the value of i, because the example includes no synchronization
and, under the rules explained in §17, the shared values of i and j
might be updated out of order.
One way to prevent this out-or-order behavior would be to declare
methods one and two to be synchronized (§8.4.3.6):
class Test {
static int i = 0, j = 0;
static synchronized void one() { i++; j++; }
static synchronized void two() {
System.out.println("i=" + i + " j=" + j);
}
}
This prevents method one and method two from being executed
concurrently, and furthermore guarantees that the shared values of i and
j are both updated before method one returns. Therefore method two never
observes a value for j greater than that for i; indeed, it always
observes the same value for i and j.
Another approach would be to declare i and j to be volatile:
class Test {
static volatile int i = 0, j = 0;
static void one() { i++; j++; }
static void two() {
System.out.println("i=" + i + " j=" + j);
}
}
This allows method one and method two to be executed concurrently, but
guarantees that accesses to the shared values for i and j occur exactly
as many times, and in exactly the same order, as they appear to occur
during execution of the program text by each thread. Therefore, the
shared value for j is never greater than that for i, because each update
to i must be reflected in the shared value for i before the update to j
occurs. It is possible, however, that any given invocation of method two
might observe a value for j that is much greater than the value observed
for i, because method one might be executed many times between the
moment when method two fetches the value of i and the moment when method
two fetches the value of j.
See §17 for more discussion and examples.
A compile-time error occurs if a final variable is also declared volatile.
--
Eclipse plug in address
http://propedit.sourceforge.jp/eclipse/
http://www.geniisoft.com/showcase.nsf/WebEditors
1.簡述邏輯操作(&,|,^)與條件操作(&&,||)的區(qū)別。(15分)
區(qū)別主要答兩點(diǎn):
a.條件操作只能操作布爾型的,而邏輯操作不僅可以操作布爾型,而且可以操作數(shù)值型
b.邏輯操作不會(huì)產(chǎn)生短路.如:
int a = 0;
int b = 0;
if( (a = 3) > 0 || (b = 3) > 0 ) //操后a =3,b=0.
if( (a = 3) > 0 | (b = 3) > 0 ) //操后a =3,b=3.
答對第一點(diǎn)得5分,答對第二點(diǎn)得10分.
本題考察最最基本的知識,但仍然有很多大牛級開發(fā)人員下馬,任何語言在開始的部分
都會(huì)詳細(xì)介紹這些基本知識,但除了學(xué)習(xí)第一種語言時(shí),沒有人在學(xué)習(xí)新的語言時(shí)愿意
花五分鐘來復(fù)習(xí)一下.
2.下面程序運(yùn)行會(huì)發(fā)生什么結(jié)果?如果有錯(cuò)誤,如何改正? (15分)
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();
}
}
}
本題在編譯時(shí)會(huì)發(fā)生錯(cuò)誤(錯(cuò)誤描述不同的JVM有不同的信息,意思就是未明確的x調(diào)用,
兩個(gè)x都匹配,就象在同時(shí)import java.util和java.sql兩個(gè)包時(shí)直接聲明Date一樣)
本題主要考察對接口和類的最最基本的結(jié)構(gòu)的了解.對于父類的變量,可以用super.x來
明確,而接口的屬性默認(rèn)隱含為 public static final.所以可以通過A.x來明確.
3.簡述 Java Server Page 和 Servlet 的聯(lián)系和區(qū)別。(20分)
本題不用多說,在答相同點(diǎn)時(shí)應(yīng)該明確知道jsp編譯后是"類servlet"而"不是Servlet",
答區(qū)別時(shí)應(yīng)該回答出"側(cè)重于(視圖/控制邏輯)".其它可根據(jù)情況加減分值.知識很簡單,
但從面試的角度看,被試者不僅要能知道它們的區(qū)別,而且要能比較準(zhǔn)確地表達(dá)出來(以
后寫文檔要能讓別人看得懂,不產(chǎn)生歧義),回答"jsp編譯后就是servlet"視為錯(cuò)誤,回答
"jsp用于視圖,servlet用于控制邏輯"視為錯(cuò)誤,應(yīng)該用側(cè)重于,主要(多數(shù))用于等詞語
表達(dá).
4.XML文檔定義有幾種形式？它們之間有何本質(zhì)區(qū)別？
解析XML文檔有哪幾種方式？(20分)
本題三個(gè)答題點(diǎn):
a: 兩種形式 dtd,schema
b: 本質(zhì)區(qū)別:schema本身是xml的,可以被XML解析器解析(這也是從DTD上發(fā)展schema的
根本目的)
c: 兩種主要方式:dom,sax.答出兩種得全分,如能答出saxt,或其它(在答出dom,sax的基
礎(chǔ)上,如果應(yīng)試者認(rèn)為其它方式也可以視為對xml的解析應(yīng)該允許.但沒有答出dom,sax把
其它方式說成是對XML的解析不得分)應(yīng)該加分.
5.簡述synchronized和java.util.concurrent.locks.Lock的異同 ？(15分)
主要相同點(diǎn):
Lock能完成synchronized所實(shí)現(xiàn)的所有功能.(其它不重要)
主要不同點(diǎn):
Lock有比synchronized更精確的線程語義和更好的性能(在相同點(diǎn)中回答此點(diǎn)也行)
synchronized會(huì)自動(dòng)釋放鎖.而Lock一定要求程序員手工釋放.并且必須在finally從句
中釋放,如果沒有答出在finally中釋放不得分.就如Connection沒有在finally中關(guān)閉一
樣.連最基本的資源釋放都做不好,還談什么多線程編程.
6.EJB規(guī)范規(guī)定EJB中禁止的操作有哪些？(15分)
共有8點(diǎn),答出下列3-4點(diǎn)得滿分.
1.不能操作線程和線程API(線程API指非線程對象的方法如notify,wait等)
2.不能操作awt
3.不能實(shí)現(xiàn)服務(wù)器功能
4.不能對靜態(tài)屬生存取.
5.不能使用IO操作直接存取文件系統(tǒng)
6.不能加載本地庫.
7.不能將this作為變量和返回.
8.不能循環(huán)調(diào)用.
7.請問在Java的線程里有個(gè)join()函數(shù)，這個(gè)函數(shù)有什么用呀？
是把調(diào)用join()的線程連結(jié)(join)到當(dāng)前線程,什么意思呢?就是當(dāng)前線程等待調(diào)用join()線程的結(jié)束.比如:當(dāng)前線程是主線程,它結(jié)的時(shí)候要求一個(gè)被調(diào)用的線程a結(jié)束,如果我們不調(diào)用a.join();那只能輪詢a的狀態(tài).
while(true){
if(!a.isAlive()) break;
sleep(500);
}
System.exet(1);
如果a線程isAlive,則等500ms繼續(xù)下一次輪巡,如果已經(jīng)不可用則結(jié)束,這種while(true)的輪詢一是占用大量的CPU時(shí)間.另一是有可能在sleep(500);時(shí),剛睡1ms時(shí),a就已經(jīng)!isAlive()了,那就多睡了499ms,浪費(fèi)了時(shí)間,而如果
a.join();
System.exit(1);
則一等a線程結(jié)束就會(huì)退出.如果沒有其它操作,主線程就不會(huì)占用CPU時(shí)間.
8當(dāng)一個(gè)對象被當(dāng)作參數(shù)傳遞到一個(gè)方法后，此方法可改變這個(gè)對象的屬性，并可返回變化后的結(jié)果，那么這里到底是值傳遞還是引用傳遞?
是值傳遞。Java 編程語言只由值傳遞參數(shù)。當(dāng)一個(gè)對象實(shí)例作為一個(gè)參數(shù)被傳遞到方法中時(shí)，參數(shù)的值就是對該對象的引用。對象的內(nèi)容可以在被調(diào)用的方法中改變，但對象的引用是永遠(yuǎn)不會(huì)改變的。
9作用域public,private,protected,以及不寫時(shí)的區(qū)別
答：區(qū)別如下：
作用域 當(dāng)前類 同一package 子孫類 其他package
public √ √ √ √
protected √ √ √ ×
friendly √ √ × ×
private √ × × ×
不寫時(shí)默認(rèn)為friendly
10ArrayList和Vector的區(qū)別,HashMap和Hashtable的區(qū)別
答：就ArrayList與Vector主要從二方面來說.
一.同步性:Vector是線程安全的，也就是說是同步的，而ArrayList是線程序不安全的，不是同步的
二.數(shù)據(jù)增長:當(dāng)需要增長時(shí),Vector默認(rèn)增長為原來一培，而ArrayList卻是原來的一半
11一.靜態(tài)內(nèi)部類可以有靜態(tài)成員，而非靜態(tài)內(nèi)部類則不能有靜態(tài)成員。
12靜態(tài)內(nèi)部類的非靜態(tài)成員可以訪問外部類的靜態(tài)變量，而不可訪問外部類的非靜態(tài)變量
13jsp有哪些動(dòng)作?作用分別是什么?
答:JSP共有以下6種基本動(dòng)作
jsp:include：在頁面被請求的時(shí)候引入一個(gè)文件。
jsp:useBean：尋找或者實(shí)例化一個(gè)JavaBean。
jsp:setProperty：設(shè)置JavaBean的屬性。
jsp:getProperty：輸出某個(gè)JavaBean的屬性。
jsp:forward：把請求轉(zhuǎn)到一個(gè)新的頁面。
jsp:plugin：根據(jù)瀏覽器類型為Java插件生成OBJECT或EMBED標(biāo)記
14remote接口和home接口主要作用
remote接口定義了業(yè)務(wù)方法，用于EJB客戶端調(diào)用業(yè)務(wù)方法
home接口是EJB工廠用于創(chuàng)建和移除查找EJB實(shí)例
15客服端調(diào)用EJB對象的幾個(gè)基本步驟
一、 設(shè)置JNDI服務(wù)工廠以及JNDI服務(wù)地址系統(tǒng)屬性
二、 查找Home接口
三、 從Home接口調(diào)用Create方法創(chuàng)建Remote接口
四、 通過Remote接口調(diào)用其業(yè)務(wù)方法
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>Binny.cn</title>
<script>
var obj=0;
var x=0;
var y=0;
var ie = (navigator.appVersion.indexOf("MSIE")!=-1);//IE
var ff = (navigator.userAgent.indexOf("Firefox")!=-1);//Firefox
function find(evt,objDiv){
obj = objDiv
if (ff){
x = document.documentElement.scrollLeft + evt.layerX;
y = document.documentElement.scrollTop + evt.layerY;
if (document.documentElement.scrollTop > 0){
y = evt.layerY - document.documentElement.scrollTop;
}
if (document.documentElement.scrollLeft > 0){
x = evt.layerX - document.documentElement.scrollLeft;
}
}
if (ie){
x = document.documentElement.scrollLeft + evt.offsetX;
y = document.documentElement.scrollTop + evt.offsetY;
if (document.documentElement.scrollTop > 0){
y = evt.offsetY - document.documentElement.scrollTop;
}
if (document.documentElement.scrollLeft > 0){
x = evt.offsetX - document.documentElement.scrollLeft;
}
}
}
function dragit(evt){
if(obj == 0){
return false
}
else{
obj.style.left = evt.clientX - x + "px";
obj.style.top = evt.clientY - y + "px";
}
}
</script>
</head>
<body style="margin:0" onmousemove="dragit(event)" onmouseup="obj = 0">
<div id="aaa" style="background-color:red;width:200pt;height:200pt;position:absolute">
<div id="aa" style="width:200pt;height:20pt;background:blue;position:absolute" onmousedown="find(event,document.getElementById('aaa'))"></div>
</div><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR>
</body>
</html>
摘自：http://www.binny.cn/article.asp?id=232
/*this can see the table information*/
show table status from `fortioa`;
/*this can see all the fields detail information of a table including the character set*/
show full fields from `account`
/*change the table column`s character set to utf8*/
ALTER TABLE `purchaserequest` CHANGE `justification` `justification` text CHARACTER SET utf8 COLLATE utf8_bin NOT NULL
--執(zhí)行這個(gè)語句,就可以把當(dāng)前庫的所有表的所有者改為dbo
exec sp_msforeachtable 'sp_changeobjectowner ''?'', ''dbo'''