synchronized方法与语句块（菜鸟玩线程）

以你之姓@ 2024-02-19 13:06 12阅读 0赞

## synchronized方法与语句块 ##

### 弊端凸显 ###

#### 定义共享变量实例类 ####

package com.chapter02.thread3;
    
    public class Task {
        
        private String getData1;
        private String getData2;
    
        synchronized public void doLongTimeTask() {
        
            try {
        
                System.out.println("BEGIN TASK!");
    
                Thread.sleep(3000);
                getData1 = "COST LONG TIME DEAL TASK RETURN VALUE 1 threadName = " + Thread.currentThread().getName();
                getData2 = "COST LONG TIME DEAL TASK RETURN VALUE 2 threadName = " + Thread.currentThread().getName();
    
                System.out.println(getData1);
                System.out.println(getData2);
    
                System.out.println("END TASK!");
            } catch (Exception ex) {
        
                ex.printStackTrace();
            }
        }
    }

#### 自定义线程1 ####

package com.chapter02.thread3;
    
    public class MyThread1 extends Thread {
        
        private Task task;
    
        public MyThread1(Task task) {
        
            this.task = task;
        }
    
        @Override
        public void run() {
        
            super.run();
            CommonUtils.beginTime1 = System.currentTimeMillis();
            task.doLongTimeTask();
            CommonUtils.endTime1 = System.currentTimeMillis();
        }
    }

#### 自定义线程2 ####

package com.chapter02.thread3;
    
    public class MyThread2 extends Thread {
        
        private Task task;
    
        public MyThread2(Task task) {
        
            this.task = task;
        }
        @Override
        public void run() {
        
            super.run();
            CommonUtils.beginTime2 = System.currentTimeMillis();
            task.doLongTimeTask();
            CommonUtils.endTime2 = System.currentTimeMillis();
        }
    }

#### CommonUtils类定义 ####

package com.chapter02.thread3;
    public class CommonUtils {
        
        public static long beginTime1;
        public static long endTime1;
        public static long beginTime2;
        public static long endTime2;
    }

启动类

package com.chapter02.thread3;
    
    public class Run {
        
        public static void main(String[] args) {
        
            Task task = new Task();
            MyThread1 myThread1 = new MyThread1(task);
            myThread1.start();
    
            MyThread2 myThread2 = new MyThread2(task);
            myThread2.start();
    
            try {
        
                Thread.sleep(10000);
            } catch (InterruptedException e) {
        
                e.printStackTrace();
            }
    
            long beginTime = CommonUtils.beginTime1;
            if (CommonUtils.beginTime2 < CommonUtils.beginTime1) {
        
                beginTime = CommonUtils.beginTime2;
            }
            long endTime = CommonUtils.endTime1;
            if (CommonUtils.endTime2 > CommonUtils.endTime1) {
        
                endTime = CommonUtils.endTime2;
            }
            System.out.println("COST TIME : " + (endTime - beginTime) / 1000 + " S ！！");
        }
    }

#### 执行结果 ####

BEGIN TASK!
    COST LONG TIME DEAL TASK RETURN VALUE 1 threadName = Thread-0
    COST LONG TIME DEAL TASK RETURN VALUE 2 threadName = Thread-0
    END TASK!
    BEGIN TASK!
    COST LONG TIME DEAL TASK RETURN VALUE 1 threadName = Thread-1
    COST LONG TIME DEAL TASK RETURN VALUE 2 threadName = Thread-1
    END TASK!
    COST TIME : 6 S ！！

#### 结论 ####

`在使用synchronized关键字来声明方法public synchronized void doLongTimeTask()方法时，从运行的时间上来看，弊端很明显，可以使用synchronized同步块。`

### 解决弊端 ###

#### 修改 ####

修改共享变量实例类，把synchronized同步方法改为同步块。。

package com.chapter02.thread3;
    public class Task {
        
        private String getData1;
        private String getData2;
    
        public void doLongTimeTask() {
        
            try {
        
                System.out.println("BEGIN TASK!");
    
                Thread.sleep(3000);
                String Data1 = "COST LONG TIME DEAL TASK RETURN VALUE 1 threadName = " + Thread.currentThread().getName();
                String Data2 = "COST LONG TIME DEAL TASK RETURN VALUE 2 threadName = " + Thread.currentThread().getName();
    
                synchronized (this) {
        
                    getData1 = Data1;
                    getData2 = Data2;
                }
    
                System.out.println(getData1);
                System.out.println(getData2);
    
                System.out.println("END TASK!");
            } catch (Exception ex) {
        
                ex.printStackTrace();
            }
        }
    }

#### 执行结果 ####

BEGIN TASK!
    BEGIN TASK!
    COST LONG TIME DEAL TASK RETURN VALUE 1 threadName = Thread-1
    COST LONG TIME DEAL TASK RETURN VALUE 2 threadName = Thread-0
    END TASK!
    COST LONG TIME DEAL TASK RETURN VALUE 1 threadName = Thread-0
    COST LONG TIME DEAL TASK RETURN VALUE 2 threadName = Thread-0
    END TASK!
    COST TIME : 3 S ！！

#### 结论 ####

时间减短。。