单例模式-代码示例

package com.example.springbootdemo.designpattern.singleton;

/**
 * 单例模式实现
 * 适用于单线程
 *
 * @author wentao
 * @time 2019年03月18日
 * @copyright Gods bless me,code never with bug.
 */
public class SingletonBySingleThread {
    private static SingletonBySingleThread instance = null;

    private SingletonBySingleThread() {

    }

    public static SingletonBySingleThread getInstance() {
        if (null == instance) {
            instance = new SingletonBySingleThread();
        }
        return instance;
    }
}


******************************************************************************

package com.example.springbootdemo.designpattern.singleton;

/**
 * 单例模式
 * 懒汉式加载
 *
 * @author wentao
 * @time 2019年03月18日
 * @copyright Gods bless me,code never with bug.
 */
public class SingletonByLazy {
    private static SingletonByLazy instance = null;

    private SingletonByLazy() {

    }

    /**
     * 此创建方法运行效率较低，用synchronized加锁解锁会比较耗时
     *
     * @param
     * @return com.example.springbootdemo.designpattern.singleton.SingletonByLazy
     * @throws
     * @author wentao
     * @time 2019年03月18日
     * Gods bless me,code never with bug.
     */
    public static synchronized SingletonByLazy getInstance() {
        if (null == instance) {
            instance = new SingletonByLazy();

        }
        return instance;
    }

    /**
     * 此创建方法相对上一个方法，效率有所提升。只用synchronized包裹住实例不存在创建的过程
     * 相比于上一个方法来说，减少了实例存在的情况下直接返回的那部分效率
     *
     * @param
     * @return com.example.springbootdemo.designpattern.singleton.SingletonByLazy
     * @throws
     * @author wentao
     * @time 2019年03月18日
     * Gods bless me,code never with bug.
     */
    public static SingletonByLazy getInstanceOtherWay() {
        if (null == instance) {
            synchronized (SingletonByLazy.class) {
                if (null == instance) {
                    instance = new SingletonByLazy();
                }
            }

        }
        return instance;
    }
}

***************************************************************************************************

package com.example.springbootdemo.designpattern.singleton;

/**
 * 单例模式-饿汉式加载
 *
 * @author wentao
 * @time 2019年03月18日
 * @copyright Gods bless me,code never with bug.
 */
public class SingletonByHungry {

    private static SingletonByHungry instance = new SingletonByHungry();
    private static String name = "饿汉式加载创建";

    private SingletonByHungry() {
    }

    public static SingletonByHungry getInstance() {
        return instance;
    }

    public void printCreaterName() {
        System.out.println("该类创建者是" + name);
    }

}

******************************************************************************************

package com.example.springbootdemo.designpattern.singleton;

/**
 * 单例模式-声明式
 * 即采用内部类形式创建
 *
 * @author wentao
 * @time 2019年03月18日
 * @copyright Gods bless me,code never with bug.
 */
public class SingletonByDeclarative {

    private SingletonByDeclarative() {

    }

    private static class Singleton {
        private final static SingletonByDeclarative instance = new SingletonByDeclarative();
    }

    public static SingletonByDeclarative getInstance() {
        return Singleton.instance;
    }
}

*****************************************************************************************

package com.example.springbootdemo.designpattern.singleton;

/**
 * 单例模式测试类
 *
 * @author wentao
 * @time 2019年03月18日
 * @copyright Gods bless me,code never with bug.
 */
public class SingletonTest {

    public static class ThreadTest implements Runnable{
        @Override
        public void run() {
            System.out.println( SingletonByLazy.getInstance());
        }
    }

    public static void main(String[] args) {
        //创建多个线程，每个线程获取一个单例模式的对象，并调用该对象的方法输出语句
        for (int i=0;i<10;i++){
            ThreadTest threadTest=new ThreadTest();
            new Thread(threadTest).start();
        }
    }

}