一、饿汉式
特性：立即创建 线程安全 没有延迟加载
public class Single {
private static Single instance=new Single();
private Single(){}
public static Single getInstance(){
return instance;
}
}
二、懒汉式
特性：延迟创建，线程不安全
public class Single {
private static Single instance;
private Single(){}
public static Single getInstance(){
if(instance==null){
instance=new Single();
}
return instance;
}
}
三、加锁的懒汉式
特性：延迟创建 线程安全 同步情况下效率低
public class Single {
private static Single instance;
private Single(){}
public synchronized static Single getInstance(){
if(instance==null){
instance=new Single();
}
return instance;
}
}
四、双重验证式懒汉式
特性：延迟创建 线程安全 同步情况下效率高
public class Single {
private static Single instance;
private Single(){}
public static Single getInstance(){
if(instance==null){
synchronized (Single.class) {
if (instance==null) {
instance=new Single();
}
}
}
return instance;
}
}
五、类加载方式
特性：延迟创建 线程安全 同步情况下效率高
public class Single {
private Single(){}
private static class ClassHolder{
private static Single instance=new Single();
}
public static Single getInstance(){
return ClassHolder.instance;
}
}
六、枚举方式
特性：原生防止反射和反序列化击穿
public enum Single{
INSTANCE;
}
