单例模式和多线程的实例:总结

我会带着你远行 2022-05-27 08:13 553阅读 0赞

最近在看 < effective java > 一边看,一遍找源码敲案例,确实有点头疼; 第一章节讲的是对象的创建和销毁 ; 讲了很多关于单例的 内容 . 于是就在想单例和线程的关系. 敲了一段demo .我们通过代码的结果来总结:  
**single domain 类**

public class SingleTest {
        private String name ;
        private final static SingleTest INSTANCE = new SingleTest();
        private SingleTest (){}
        private SingleTest(String name){
            this.name = name;
        }
    
        public static SingleTest getInstantce(){
            return INSTANCE;
        }
        // 以下get set
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
       /* @Override public String toString() { return "SingleTest{" + "name='" + name + '\'' + '}'; }*/
    }

**线程A:**

public class ThreadA implements Runnable{ 
        @Override
        public void run() {
            SingleTest instantce = SingleTest.getInstantce();
            System.out.println("Thread_A_Instance : "+instantce);
            instantce.setName("12");
    
            System.out.println("Threand_A_SetName = "+"12");
        }
    }

**线程B**

public class ThreadB implements Runnable { 
    
        @Override
        public void run() {
            SingleTest instantce = SingleTest.getInstantce();
            System.out.println("Thread_B_Instance : "+instantce);
            System.out.println("Thread_B_GetName = "+instantce.getName());
    
        }
    }

**单元测试**

@Test
        public void testInstance(){
            Thread thread = new Thread(new ThreadA());
            Thread thread1 = new Thread(new ThreadB());
            thread.start();
            thread1.start();
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            while (true){
    
            }
        }

**输出:**

Thread_A_Instance : com.ding.domain.SingleTest@35060f17
    Thread_B_Instance : com.ding.domain.SingleTest@35060f17
    Threand_A_SetName = 12
    Thread_B_GetName = 12

这边可以说明:

1.  在系统运行时,单例即使在不同的线程中,也只会有一个对象
2.  在多个线程中单例对象的数据可以共享.
3.  在多线程并发时 ,单例对象的性能 ,以及加锁应该在考虑范围之类.