编程小知识点范例-2

http://tianya23.blog.51cto.com/1081650/591809

 

【注】

windows设置环境变量，例如设置jdk为1.7.0版本（一定要把%path%加上）：

set path="D:\ProgramFiles\Java\jdk1.7.0\bin";%path%

 

1、取得当前进程下的所有线程

public static String[] getThreadNames() {
        ThreadGroup group = Thread.currentThread().getThreadGroup();
        ThreadGroup parent = null;
        while ((parent = group.getParent()) != null) {
            group = parent;
        }
        Thread[] threads = new Thread[group.activeCount()];
        group.enumerate(threads);
        java.util.HashSet<String> set = new java.util.HashSet<String>();
        for (int i = 0; i < threads.length; ++i) {
            if (threads[i] != null && threads[i].isAlive()) {
                try {
                    set.add(threads[i].getThreadGroup().getName() + ","
                            + threads[i].getName() + ","
                            + threads[i].getPriority());
                } catch (Throwable e) {
                    e.printStackTrace();
                }
            }
        }
        String[] result = (String[]) set.toArray(new String[0]);
        java.util.Arrays.sort(result);
        return result;
    }

 2、Java多线程--让主线程等待所有子线程执行完毕

参考：http://3ccoder.iteye.com/blog/581476

public class ImportThread extends Thread {
private CountDownLatch threadsSignal;
public ImportThread(CountDownLatch threadsSignal) {
this.threadsSignal = threadsSignal;
}
@Override
public void run() {
System.out.println(Thread.currentThread().getName() + "开始...");
//Do somethings
threadsSignal.countDown();//线程结束时计数器减1
System.out.println(Thread.currentThread().getName() + "结束. 还有" + threadsSignal.getCount() + " 个线程");
}
}

 

 main：

CountDownLatch threadSignal = new CountDownLatch(threadNum);//初始化countDown
for (int ii = 0; ii < threadNum; ii++) {//开threadNum个线程
final Iterator<String> itt = it.get(ii);
Thread t = new ImportThread(itt,sql,threadSignal);
t.start();
}
threadSignal.await();//等待所有子线程执行完
System.out.println(Thread.currentThread().getName() + "结束.");//打印结束标记

 

3、生产者消费者问题

public class ProducerTest {
    public static void main(String[] args) {
        Queue q = new Queue();
        Producer t1 = new Producer(q);
        Consumer t2 = new Consumer(q);
        t1.start();
        t2.start();
    }
}

class Producer extends Thread {
    Queue q;

    public Producer(Queue q) {
        this.q = q;
    }

    public void run() {
        for (int i = 0; i < 10; i++) {
            q.put(i);
            System.out.println("Producer put:" + i);
        }
    }
}

class Consumer extends Thread {
    Queue q;

    public Consumer(Queue q) {
        this.q = q;
    }

    public void run() {
        while (true) {
            System.out.println("Consumer get:" + q.get());
        }
    }
}

class Queue {
    int     value;
    boolean bFull = false;

    public synchronized void put(int i) {
        if (!bFull) {
            value = i;
            bFull = true;
            notify();
        }
        try {
            wait();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public synchronized int get() {
        if (!bFull) {
            try {
                wait();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        bFull = false;
        notify();
        return value;

    }
}

 4、Comparable接口使用

class Student implements Comparable
{
    int num;
    String name;
    static class StudentComparator implements Comparator
    {
        public int compare(Object o1,Object o2)
        {
            Student s1=(Student)o1;
            Student s2=(Student)o2;
            int result=s1.num > s2.num ? 1 : (s1.num==s2.num ? 0 : -1);
            if(result==0)
            {
                result=s1.name.compareTo(s2.name);
            }
            return result;
        }
    }
    Student(int num,String name)
    {
        this.num=num;
        this.name=name;
    }

    public int compareTo(Object o)
    {
        Student s=(Student)o;
        return num > s.num ? 1 : (num==s.num ? 0 : -1);
    }
    public String toString()
    {
        return num+":"+name;
    }
}

 如要求先name，后age，则可参考如下：

class Student implements Comparable<Object> {
    private String name;
    private int age;

    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }

    @Override
    public int compareTo(Object o) {
        Student student = null;
        if (o instanceof Student) {
            student = (Student) o;
        }
        int ret1 = this.name.compareTo(student.name);
        // int ret2 = this.age - student.age;
        return ret1 != 0 ? ret1 : (this.age > student.age ? 1
                : (this.age == student.age ? 0 : -1));

    }
}

 5、配置文件覆盖方法

String requestedFile = System.getProperty(PROPERTIES_FILE);
        String propFileName = requestedFile != null ? requestedFile
                : "quartz.properties";

 6、static final

一个既是static又是final的字段只占据一段不能改变的存储空间。 带有恒定初始值（即，编译时常量）的static final基本类型全用大写字母命名，并且字与字之间用下划线隔开。如java.lang.byte类里对byte类型的最小值定义：

public  static  final  byte     MIN_VALUE  = -128;

更多参考：http://blog.csdn.net/tiannet/article/details/2593472