单例模式
单例模式结构
实现单例模式的5种方式：
1.饿汉式单例（立即加载方式）
public class Singleton{
private Singleton(){};
private static Singleton single = new Singleton();
public static Singleton getInstance(){
return single;
}
}
2.懒汉式单例（延迟加载方式）
public class Singleton{
private Singleton(){};
private static Singleton single =null ;
public static Singleton getInstance(){
if(Singleton == null){
Singleton = new Singleton();
}
return Singleton ;
}
}
多线程环境下使用syhchronized
public class Singleton{
private Singleton(){};
private static Singleton single =null ;
public static Singleton getInstance(){
// 等同于 synchronized public static Singleton getInstance()
syhchronized(Singleton.class){
if(Singleton == null){
Singleton = new Singleton();
}
}
return Singleton ;
}
}
利用双重检查提高效率
public class Singleton{
private Singleton(){};
private static Singleton single =null ;
public static Singleton getInstance(){
if(Singleton == null){
syhchronized(Singleton.class){
if(Singleton == null){
Singleton = new Singleton();
}
}
}
return Singleton ;
}
}
3.静态内部类实现
public class Singleton{
private Singleton(){};
private static class InnerClass {
private static Singleton single =new Singleton();
}
public static Singleton getInstance(){
return InnerClass .single;
}
}
4.静态代码块
public class Singleton{
private Singleton(){};
private static Singleton single =null ;
static {
single = new Singleton();
}
public static Singleton getInstance(){
return single;
}
}
5.内部枚举类实现
public class SingletonFactory {
// 内部枚举类
private enum EnmuSingleton{
Singleton;
private Singleton singleton;
//枚举类的构造方法在类加载是被实例化
private EnmuSingleton(){
singleton = new Singleton();
}
public Singleton getInstance(){
return singleton;
}
}
public static Singleton getInstance() {
return EnmuSingleton.Singleton.getInstance();
}
}
class Singleton{
public Singleton(){}
}
