单例设计模式懒汉式和恶汉式

一,单例设计模式懒汉式和恶汉式

懒汉式在类加载时不初始化，延迟加载。（配置文件）

饿汉式在类加载时初始化，加载慢，获取对象快。

饿汉式是线程安全的，

懒汉式需要加synchronized，否则不安全。

二，饿汉式

public class Singletonehan {
    private static  Singletonehan singleton=new Singletonehan();
    private Singletonehan() {
    }
public static Singletonehan getInstance(){
        return singleton;
}

    @Override
    public String toString() {
        return "Singletonehan{}";
    }
}

测试

public class testehan {
    public static void main(String[] args) {
        Singletonehan singletonehan = Singletonehan.getInstance();
        System.out.println(singletonehan);
    }
}

三，懒汉式

public class Singletonlanhan {
   // private static  Singletonlanhan singleton=new Singletonlanhan();
    private static  Singletonlanhan singleton=null;

    private Singletonlanhan() {
    }

    public static Singletonlanhan getInstance() {
        if (singleton == null) {
            singleton = new Singletonlanhan();
        }
        return singleton;
    }

    @Override
    public String toString() {
        return "Singletonlanhan{}";
    }
}

测试

public class test {
    public static void main(String[] args) {
        Singletonlanhan singletonlanhan = Singletonlanhan.getInstance();
        System.out.println(singletonlanhan);
    }
}

结果

Singletonlanhan{}

Process finished with exit code 0

补充加synchronized后的懒汉

public class Singletonlanhan {
   // private static  Singletonlanhan singleton=new Singletonlanhan();
    private static  Singletonlanhan singleton=null;

    private Singletonlanhan() {
    }

    public synchronized static Singletonlanhan getInstance() {
        if (singleton == null) {
            singleton = new Singletonlanhan();
        }
        return singleton;
    }

    @Override
    public String toString() {
        return "锁Singletonlanhan{}";
    }
}

结果

锁Singletonlanhan{}

Process finished with exit code 0