java中都有哪些是单例的
时间: 2023-10-21 11:07:18 浏览: 41
在Java中,常见的单例模式实现方式有以下几种:
1. 饿汉式(线程安全,类加载时就初始化):
```
public class Singleton {
private static Singleton instance = new Singleton();
private Singleton() {}
public static Singleton getInstance() {
return instance;
}
}
```
2. 懒汉式(线程不安全,需要时才初始化):
```
public class Singleton {
private static Singleton instance = null;
private Singleton() {}
public static Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
```
3. 双重校验锁式(线程安全,延迟初始化,使用双重检查锁机制):
```
public class Singleton {
private volatile static Singleton instance = null;
private Singleton() {}
public static Singleton getInstance() {
if (instance == null) {
synchronized (Singleton.class) {
if (instance == null) {
instance = new Singleton();
}
}
}
return instance;
}
}
```
4. 静态内部类式(线程安全,延迟初始化,使用静态内部类实现懒加载):
```
public class Singleton {
private static class SingletonHolder {
private static final Singleton INSTANCE = new Singleton();
}
private Singleton() {}
public static Singleton getInstance() {
return SingletonHolder.INSTANCE;
}
}
```
5. 枚举式(线程安全,防止反序列化生成新的实例,且可以防止反射攻击):
```
public enum Singleton {
INSTANCE;
public void doSomething() {
// ...
}
}
```
以上是常见的几种单例模式实现方式。