📄 singleton.html
字号:
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<META name="description" content="Java,JDBC,EJB,Open Source,jdk,rmi">
<meta name="Keywords" content="Java, servlets, Java servlet, Javascript, ActiveX, VRML,
applet, applets, directory, news, jdbc, applications,
Java applications, Java developer, Java development, developer,
classes, Jars.com, Jars, intranet, Java applet, Javabeans,
Java products, JDK, Java development kit, java development environment, JIT,
JavaPlan, enterprise tools, JVM, Java Virtual Machine, Java resources,
SUN, CGI, Perl, database, network, html,
xml, dhtml, rating, ratings, review, jars, cgi, programming,
software review, software rating">
<title>csdn_Singleton模式 </title>
<style>
.news { BACKGROUND: #007cd3; font-family: "宋体"; font-size: 9pt }
.t { font-family: "宋体"; font-size: 9pt }
.t1 { color:#007cd3; font-family: "宋体"; font-size: 9pt }
.white { font-family: "宋体"; font-size: 9pt;color:#FFFFFF }
.red { font-family: "宋体"; font-size: 9pt;color:#FF0000 }
A {text-decoration: underline}
A:visited {color:#0000FF}
A:hover {color: #ff6666; text-decoration: none}
.text {font-size: 12px; line-height: 160%; font-family: "宋体"}
.text1 {color:#000000; font-size: 12px; line-height: 130%; font-family: "宋体"; text-decoration: none}
.text1:visited {color:#000000}
.text1:hover {color: #000000}
.text2 {color:#000000; font-size: 12px; line-height: 130%; font-family: "宋体"; text-decoration: none}
.text2:visited {color:#000000}
.text2:hover {color: #000000}
.text3 {font-size: 12px; line-height: 100%; font-family: "宋体"; text-decoration: none}
.large {font-size: 14.8px; line-height: 130%}
</style>
</head>
<!--start first table -->
<TR>
<TD WIDTH="20%" VALIGN="TOP">
<TR>
<TD WIDTH="20%" CLASS="t" BGCOLOR="#007cd3" align="Center"></TD>
<TR>
<TR>
<TD WIDTH="20%" CLASS="t" align="center" >
</TD>
<TR>
</td>
<TD WIDTH="100%" VALIGN="TOP" >
<TR>
<TD WIDTH="100%" CLASS="white"></TD>
<TR>
<TR>
<TD WIDTH="50%" bordercolor="#FFFFFF" CLASS="t1" bgcolor="#F0F0F0" nowrap >Java中设计模式(2) Singleton模式
</TD>
<p> <TD WIDTH="50%" bordercolor="#FFFFFF" CLASS="t1" bgcolor="#F0F0F0" nowrap >作者：jdeveloper
</TD> </p>
<TR>
<TR>
<TD WIDTH="100%" bordercolor="#FFFFFF" CLASS="t" bgcolor="#F0F0F0" colspan=2>
<pre>
Singleton模式:
Singleton模式主要作用是保证在Java应用程序中，一个Class只有一个实例存在。
一般有三种方法：
<font color=red>1</font> 定义一个类，它的构造函数为private的，所有方法为static的。如java.lang.Math
其他类对它的引用全部是通过类名直接引用。例如：
public final class Math {
/**
* Don't let anyone instantiate this class.
*/
private Math() {}
public static int round(float a) {
return (int)floor(a + 0.5f);
}
...
}
<font color=red>2</font> 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。例如：
public class Runtime {
private static Runtime currentRuntime = new Runtime();
public static Runtime getRuntime() {
return currentRuntime;
}
...
}
<font color=red>3</font> 定义一个类，它的构造函数为private的，它有一个static的private的boolean变量,用于表示
是否有实例存在。例如：
class PrintSpooler
{
//this is a prototype for a printer-spooler class
//such that only one instance can ever exist
static boolean
instance_flag=false; //true if 1 instance
public PrintSpooler() throws SingletonException
{
if (instance_flag)
throw new SingletonException("Only one spooler allowed");
else
instance_flag = true; //set flag for 1 instance
System.out.println("spooler opened");
}
//-------------------------------------------
public void finalize()
{
instance_flag = false; //clear if destroyed
}
}
</pre>
</TD>
<TR>
</TD>
</TR>
<!--end first table -->
</center>
</body>
</html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -