java 单例模式

public class SingleOne {
//懒汉式单例,线程不安全
private static SingleOne single = null;
private SingleOne(){}//设置成私有防止外键new一个对象
public static SingleOne getInstance(){
if(single == null){
System.out.println("new single");
single =  new SingleOne();
}
return single;
}

}

public class SingleTwo {
//饿汉式单例,线程安全
private static final SingleTwo single = new SingleTwo();
private SingleTwo(){}
public static SingleTwo getInstance(){
System.out.println("new single ");
return single;
}
}