单例模式在实际开发过程中经常会用到,我们有必要充分的理解单例模式。单例模式有多种写法,分为懒汉式、饿汉式、双重锁等。
public class Singleton1 {
//私有的默认构造子
private Singleton() {}
//已经自行实例化
private static final Singleton single = new Singleton();
//静态工厂方法
public static Singleton getInstance() {
return single;
}
}
public class Singleton {
private static Singleton instance;
private Singleton (){}
public static Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
public class Singleton {
private static Singleton instance;
private Singleton (){}
public static synchronized Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
public class Singleton {
private static class SingletonHolder {
private static final Singleton INSTANCE = new Singleton();
}
private Singleton (){}
public static final Singleton getInstance() {
return SingletonHolder.INSTANCE;
}
}
public class Singleton {
private volatile static Singleton singleton;
private Singleton() {
}
public static Singleton getSingleton() {
if (singleton == null) {
synchronized (Singleton.class) {
if (singleton == null) {
singleton = new Singleton();
}
}
}
return singleton;
}
}
单例模式使用的一个实际例子见下一篇。