设计模式之单例模式

1.饿汉式-线程不安全

public class People{
    private static People people=new People();
    private People(){
        
    }
    public static People getInstance(){
        return people;
    } 
}

2.懒汉式-线程不安全

public class People{
    private static People people;
    private People(){}
    public static People getInstance(){
        if(people==null){
            people=new People();
        }
        return people;
    }
}

3.加锁-不够灵活

public class People{
    private static People people;
    private People(){}
    public synchronized static People getInstance(){
        if(people==null){
            people=new People();
        }
        return people;
    }
}

4.加锁-灵活

public class People{
    private static People people;
    private People(){}
    public synchronized static People getInstance(){
        synchronized(People.class){
            if(people==null){
            	people=new People();
        	}
        }
        return people;
    }
}

5.双端检索

加锁之后如果两个线程抢锁，导致一个线程创建了对象另一个线程在等待，等待结束后也创建了对象这种情况可以使用双端检索

public class People{
    private volatile static People people;
    private People(){
        
    }
    public static People getInstance(){
        if(people==null){
            synchronized(People.class){
                if(people==null){
                    people=new People();
                }
            }
        }
        return people;
    }
}

6.静态内部类

public class People{
    private People(){}
    static class inner{
        private final static People people=new People();
    }
    public static People getInstance(){
        return inner.people;
    }
}

请使用5,6