Java中的并发编程：从基础到高级技巧
并发编程在Java中是一个非常重要且复杂的主题。随着多核处理器的普及，并发编程技术的掌握成为Java高级软件工程师必备的技能。本文将从基础知识入手，逐步深入探讨Java中的并发编程技巧，并通过代码示例进行详细讲解。
一、并发编程基础
1. 线程和Runnable接口
在Java中，线程是并发编程的基本单位。可以通过继承Thread类或实现Runnable接口来创建线程。
package cn.juwatech.concurrency;
public class BasicThreadExample {
public static void main(String[] args) {
Thread thread = new Thread(new RunnableTask());
thread.start();
}
}
class RunnableTask implements Runnable {
@Override
public void run() {
System.out.println("Hello from a thread!");
}
}2. 线程同步
在多线程环境中，多个线程可能会同时访问共享资源，导致数据不一致。使用同步机制可以避免这种情况。Java提供了synchronized关键字来实现线程同步。
package cn.juwatech.concurrency;
public class SynchronizedExample {
private int count = 0;
public synchronized void increment() {
count++;
}
public static void main(String[] args) {
SynchronizedExample example = new SynchronizedExample();
Thread thread1 = new Thread(() -> {
for (int i = 0; i < 1000; i++) {
example.increment();
}
});
Thread thread2 = new Thread(() -> {
for (int i = 0; i < 1000; i++) {
example.increment();
}
});
thread1.start();
thread2.start();
try {
thread1.join();
thread2.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Final count: " + example.count);
}
}二、并发编程高级技巧
1. 使用Lock接口
相比synchronized，Lock接口提供了更灵活的锁机制。ReentrantLock是Lock接口的常用实现。
package cn.juwatech.concurrency;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class LockExample {
private int count = 0;
private final Lock lock = new ReentrantLock();
public void increment() {
lock.lock();
try {
count++;
} finally {
lock.unlock();
}
}
public static void main(String[] args) {
LockExample example = new LockExample();
Thread thread1 = new Thread(() -> {
for (int i = 0; i < 1000; i++) {
example.increment();
}
});
Thread thread2 = new Thread(() -> {
for (int i = 0; i < 1000; i++) {
example.increment();
}
});
thread1.start();
thread2.start();
try {
thread1.join();
thread2.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Final count: " + example.count);
}
}2. 使用线程池
线程池可以有效管理和复用线程资源，避免频繁创建和销毁线程的开销。Java提供了ExecutorService接口来管理线程池。
package cn.juwatech.concurrency;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ThreadPoolExample {
public static void main(String[] args) {
ExecutorService executor = Executors.newFixedThreadPool(2);
for (int i = 0; i < 5; i++) {
executor.submit(new Task(i));
}
executor.shutdown();
}
}
class Task implements Runnable {
private final int taskId;
public Task(int taskId) {
this.taskId = taskId;
}
@Override
public void run() {
System.out.println("Task " + taskId + " is running");
}
}3. 并发容器
Java的java.util.concurrent包提供了多种线程安全的并发容器，如ConcurrentHashMap、CopyOnWriteArrayList等，简化了多线程环境下的开发。
package cn.juwatech.concurrency;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ConcurrentMapExample {
public static void main(String[] args) {
ConcurrentHashMap<Integer, String> map = new ConcurrentHashMap<>();
ExecutorService executor = Executors.newFixedThreadPool(2);
executor.submit(() -> {
for (int i = 0; i < 5; i++) {
map.put(i, "Value " + i);
System.out.println("Put: " + i);
}
});
executor.submit(() -> {
for (int i = 0; i < 5; i++) {
System.out.println("Get: " + map.get(i));
}
});
executor.shutdown();
}
}4. 原子变量
java.util.concurrent.atomic包提供了一些原子变量类，如AtomicInteger、AtomicLong等，保证了在多线程环境下的原子性操作。
package cn.juwatech.concurrency;
import java.util.concurrent.atomic.AtomicInteger;
public class AtomicExample {
private AtomicInteger count = new AtomicInteger(0);
public void increment() {
count.getAndIncrement();
}
public static void main(String[] args) {
AtomicExample example = new AtomicExample();
Thread thread1 = new Thread(() -> {
for (int i = 0; i < 1000; i++) {
example.increment();
}
});
Thread thread2 = new Thread(() -> {
for (int i = 0; i < 1000; i++) {
example.increment();
}
});
thread1.start();
thread2.start();
try {
thread1.join();
thread2.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Final count: " + example.count.get());
}
}三、总结
本文介绍了Java中的并发编程，从基础的线程和同步机制，到高级的Lock接口、线程池、并发容器和原子变量。掌握这些技术，有助于开发高效、可靠的并发应用。
