单例模式的另外三种方法

单例模式的另外三种方法

静态内部类：

public class MyObject {

    private static class MyObjectHandler{
        private static MyObject myObject = new MyObject();
    }

    private MyObject() {

    }

    public static MyObject getInstance() {
        return MyObjectHandler.myObject;
    }
}

静态内部类反序列化问题：

import java.io.ObjectStreamException;
import java.io.Serializable;

import com.stono.thread2.ThreadPrint;

public class MyObject implements Serializable {

    private static final long serialVersionUID = -3968427143706472470L;

    private static class MyObjectHandler{
        private static final MyObject myObject = new MyObject();
    }

    private MyObject() {

    }

    public static MyObject getInstance() {
        return MyObjectHandler.myObject;
    }
    
    protected Object readResolve() throws ObjectStreamException{
        ThreadPrint.print("调用了readResolve方法");
        return MyObjectHandler.myObject;
    }
}

static代码块：

public class MyObject {
    private static MyObject myObject =  null;

    private MyObject() {

    }
    static {
        myObject = new MyObject();
    }

    public static MyObject getInstance() {
        return myObject;
    }
}

enum枚举类型：

import java.util.Date;

import com.stono.thread2.ThreadPrint;

public enum MyObject {

    connectionFactory;
    private Date connection;
    private MyObject() {
        try {
            ThreadPrint.print("调用了MyObject的构造函数");
            connection = new Date();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public Date getConnection() {
        return connection;
    }
}

单一职责：

import java.util.Date;

import com.stono.thread2.ThreadPrint;

public class MyObject {

    public enum MyEnumSingleton{
        connectionFactory;
        private Date connection;
        private MyEnumSingleton() {
            try {
                ThreadPrint.print("调用了MyObject的构造函数");
                connection = new Date();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        public Date getConnection() {
            return connection;
        }
    }
    
    public static Date getConnection() {
        return MyEnumSingleton.connectionFactory.getConnection();
    }
}