设计模式 - 单件模式(singleton pattern) 具体解释

单件模式(singleton pattern) 具体解释

本文地址: http://blog.csdn.net/caroline_wendy/article/details/28595349

单件模式(singleton pattern) : 确保一个类仅仅有一个实例, 并提供一个全局訪问点.

单位价格模式包含3个部分: 私有构造器, 静态变量, 静态方法.

具体方法:

1. 标准的单例模式:

/**
* @time 2014.6.5
*/
package singleton;/**
* @author C.L.Wang
*
*/
public class Singleton {
private static Singleton uniqueInstance; //静态变量private Singleton() {} //私有构造函数public static Singleton getInstance() { //静态方法
if (uniqueInstance == null)
uniqueInstance = new Singleton();
return uniqueInstance;
}}


2. 考虑多线程的三种方法:

同步(synchronized)方法, 加入"synchronized",  会导致性能下降, 每次调用演示样例, 都须要同步, 可是使用简单.

/**
* @time 2014.6.5
*/
package singleton;/**
* @author C.L.Wang
*
*/
public class Singleton {
private static Singleton uniqueInstance; //静态变量private Singleton() {} //私有构造函数public static synchronized Singleton getInstance() { //静态方法
if (uniqueInstance == null)
uniqueInstance = new Singleton();
return uniqueInstance;
}}


急切(eagerly)方法, 開始时创建实例, 会在不须要时, 占用实例空间, 即占用空间时间过长.

/**
* @time 2014.6.5
*/
package singleton;/**
* @author C.L.Wang
*
*/
public class Singleton {
private static Singleton uniqueInstance = new Singleton(); //静态变量private Singleton() {} //私有构造函数public static synchronized Singleton getInstance() { //静态方法
//if (uniqueInstance == null)
//uniqueInstance = new Singleton();
return uniqueInstance;
}}


双重检查加锁(double-checked locking)方法, 使用"volatile"和"synchronized (Singleton.class)", 降低时间消耗, 适用于java1.4以上版本号.

/**
* @time 2014.6.5
*/
package singleton;/**
* @author C.L.Wang
*
*/
public class Singleton {
private volatile static Singleton uniqueInstance; //静态变量private Singleton() {} //私有构造函数public static synchronized Singleton getInstance() { //静态方法
if (uniqueInstance == null) {
synchronized (Singleton.class) {
if (uniqueInstance == null)
uniqueInstance = new Singleton();
}
}
return uniqueInstance;
}}


3. 使用单件模式的样例:

代码:

/**
* @time 2014.6.5
*/
package singleton;/**
* @author C.L.Wang
*
*/
public class ChocolateBoiler { //巧克力锅炉
private boolean empty;
private boolean boiled;public static ChocolateBoiler uniqueInstance; //静态变量private ChocolateBoiler() { //私有构造函数
empty = true;
boiled = false;
}public static ChocolateBoiler getInstance() { //静态方法
if (uniqueInstance == null)
uniqueInstance = new ChocolateBoiler();
return uniqueInstance;
}public void fill() { //填满
if (isEmpty()) {
empty = false;
boiled = false;
}
}public void drain() { //倾倒
if (!isEmpty() && isBoiled())
empty = true;
}public void boil() { //煮
if (!isEmpty() && !isBoiled()) {
boiled = true;
}
}public boolean isEmpty() {
return empty;
}public boolean isBoiled() {
return boiled;
}}


4. 枚举单件(enum singleton)模式, 也能够保证线程安全.

代码:

/**
* @time 2014.6.5
*/
package singleton;/**
* @author C.L.Wang
*
*/
public class EnumSingleton {/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stubeSingleton d1 = eSingleton.INSTANCE;
d1.setName("Spike");eSingleton d2 = eSingleton.INSTANCE;
d2.setName("Caroline");System.out.println(d1);
System.out.println(d2);System.out.println(d1 == d2);
}}enum eSingleton {INSTANCE;private String name;public String getName() {
return name;
}public void setName(String name) {
this.name = name;
}@Override
public String toString() {
return "[" + name + "]";
}
}

输出:

[Caroline]
[Caroline]
true