1、确保一个类只有一个实例，并提供一个全局的访问点
2、饱汉式单例实现
package com.shma.singleton;
/**
* 饱汉式单例实现
* @author admin
*
*/
public class Singleton01 {
private static Singleton01 uniqueInstance = new Singleton01();
private Singleton01() {
}
public static Singleton01 getInstance() {
return uniqueInstance;
}
}
3、饿汉式单例实现
package com.shma.singleton;
/**
* 饿汉式单例双锁机制
* @author admin
*
*/
public class Singleton02 {
private volatile static Singleton02 uniqueInstance = null;
private Singleton02() {
}
public static Singleton02 getInstance() {
if(uniqueInstance == null) {
synchronized (Singleton02.class) {
if(uniqueInstance == null) {
uniqueInstance = new Singleton02();
}
}
}
return uniqueInstance;
}
}
4、实现巧克力锅炉类，巧克力锅炉是一个单例类
package com.shma.singleton.chocolate;
/**
* 巧克力加工锅炉类
* @author admin
*
*/
public class ChocolateBoiler {
//记录锅炉内原料是否为空
private boolean empty = false;
//记录锅炉内原料是否煮沸
private boolean boiled = false;
private volatile static ChocolateBoiler uniqueInstance = null;
private ChocolateBoiler() {
}
public static ChocolateBoiler getInstance() {
if(uniqueInstance == null) {
synchronized (ChocolateBoiler.class) {
if(uniqueInstance == null) {
uniqueInstance = new ChocolateBoiler();
}
}
}
System.out.println("Returning instance of Chocolate Boiler");
return uniqueInstance;
}
/**
* 装满锅炉
* 原料为空
*/
public void fill() {
if (isEmpty()) {
empty = false;
boiled = false;
// fill the boiler with a milk/chocolate mixture
}
}
/**
* 排出成品
* 原料不能为空并且已经被煮沸
*/
public void drain() {
if (!isEmpty() && isBoiled()) {
// drain the boiled milk and chocolate
empty = true;
}
}
/**
* 煮沸方法
* 条件是锅炉原料不能为空并且没有被煮沸过
*/
public void boil() {
if (!isEmpty() && !isBoiled()) {
// bring the contents to a boil
boiled = true;
}
}
public boolean isEmpty() {
return empty;
}
public boolean isBoiled() {
return boiled;
}
}
package com.shma.singleton.chocolate;
public class ChocolateController {
public static void main(String[] args) {
ChocolateBoiler boiler = ChocolateBoiler.getInstance();
//装入原料
boiler.fill();
//煮沸
boiler.boil();
//排出
boiler.drain();
// will return the existing instance
ChocolateBoiler boiler2 = ChocolateBoiler.getInstance();
}
}
原文：http://my.oschina.net/shma1664/blog/400838