7 years ago a minute read (About 174 words)

Java类与对象初始化过程

看看如下代码，输出结果是啥？

/**
 * @author Junlan Shuai[shuaijunlan@gmail.com].
 * @date Created on 18:59 2018/4/1.
 */
public class Test {
    public static int k = 0;
    public static Test t1 = new Test("t1");
    public static Test t2 = new Test("t2");
    public static int i = print("i");
    public static int n = 99;
    public int j = print("j");
    static {
        print("静态块");
    }
    public Test(String string){
        System.out.println((++k) + ":" + string + " i=" + i + " n=" + n);
        ++i;
        ++n;
    }
    {
        print("构造块");
    }
    public static int print(String string){
        System.out.println((++k) + ":" + string + " i=" + i + " n=" + n);
        ++n;
        return ++i;
    }

    public static void main(String[] args) {
        Test test = new Test("init");
    }
}

7 years ago a minute read (About 197 words)

How-to-understand-the-DeadLock

如何理解如下代码会造成DeadLock

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * @author Junlan Shuai[shuaijunlan@gmail.com].
 * @date Created on 10:36 2018/4/14.
 */
public class DeadLock {
    static class Friend{
        private final String name;
        public Friend(String name){
            this.name = name;
        }

        public String getName(){
            return this.name;
        }

        public synchronized void bow(Friend friend){
            System.out.format("%s:%s" + " has bowed to me!%n", this.name, friend.getName());
            friend.bowBack(this);
        }
        public synchronized void bowBack(Friend friend){
            System.out.format("%s:%s" + " has bowed back to me!%n", this.name, friend.getName());
        }
    }

    public static void main(String[] args) throws InterruptedException {
        final Friend friendA = new Friend("Shuai");
        final Friend friendB = new Friend("Junlan");
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2,
                2, 1000L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<>(2));
        /// Why not using this way to create ThreadPool?
        // ExecutorService fixedThreadPool = Executors.newFixedThreadPool(2);
        threadPoolExecutor.execute(() -> friendA.bow(friendB));
        threadPoolExecutor.execute(() -> friendB.bow(friendA));
        threadPoolExecutor.shutdown();

    }
}

output

Shuai:Junlan has bowed to me!
Junlan:Shuai has bowed to me!

Conclusion

类的实例对类中所有的synchronized方法都持有锁；（表述不够官方）

8 years ago

java

5 minutes read (About 675 words)

analyse the source code of Timer

Timer Class Introduction

在JDK库中Timer类主要负责计划任务的功能，也就是在指定的时间开始执行某任务。

8 years ago 4 minutes read (About 596 words)

Java创建线程的三种方式(Thread/Runnable/Callable)

1.继承Thread类

此方式只需要重写Thread类中的run()方法即可，示例如下：

/**
 * @author Junlan Shuai[shuaijunlan@gmail.com].
 * @date Created on 19:41 2017/4/10.
 */
public class ExtendThread extends Thread
{
    String name;
    public ExtendThread(String name)
    {
        this.name = name;
    }
    @Override
    public void run()
    {
        System.out.println(name);
    }
}

8 years ago 4 minutes read (About 606 words)

Collections.sort()源码分析（基于jdk1.8）

Collections类中定义了一系列的静态方法，其中就包括sort方法(下面为该方法的源码),从这个方法的源码中可以看出，它调用的是list.sort()方法，在该方法中先将list转换成数组，然后调用Arrays.sort()方法。在Arrays.sort()方法中，有一个条件判断（LegacyMergeSort.userRequested），当此条件为true时，调用legacyMergeSort(a, c);若为false则调用TimSort.sort(a, 0, a.length, c, null, 0, 0);通过legacyMergeSort(a, c);源码就可以看出此方法实现的是归并排序，