Java Multi-threaded programming involves creating and managing threads to enable concurrent execution. It covers the basic concepts of threads, synchronization, thread pools, and practical examples: Threads are lightweight processes that share memory space and allow concurrent execution. Synchronization secures access to shared resources through locks or atomic operations. Thread pools manage threads, improve performance, and reduce creation and destruction overhead. Practical example uses multi-threading to scan files in a directory in parallel.
Essential knowledge points for Java multi-threaded programming interviews
1. Basic concepts of threads
Code example:
class MyThread extends Thread { public void run() { System.out.println("This is a thread"); } } public class Main { public static void main(String[] args) { MyThread thread = new MyThread(); thread.start(); } }
2. Thread synchronization
Code example (using synchronized):
class Counter { private int count; public synchronized void increment() { count++; } public synchronized int getCount() { return count; } } public class Main { public static void main(String[] args) { Counter counter = new Counter(); Thread thread1 = new Thread(() -> { for (int i = 0; i < 10000; i++) { counter.increment(); } }); Thread thread2 = new Thread(() -> { for (int i = 0; i < 10000; i++) { counter.increment(); } }); thread1.start(); thread2.start(); thread1.join(); thread2.join(); System.out.println(counter.getCount()); // 输出:20000 } }
3. Thread pool
Code example (using ThreadPoolExecutor):
ExecutorService executor = Executors.newFixedThreadPool(5); for (int i = 0; i < 10; i++) { executor.submit(() -> { System.out.println("This is a thread from the pool"); }); } executor.shutdown();
4. Practical case: file scanning
Code example:
import java.io.File; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class FileScanner { private static void scan(File dir) { File[] files = dir.listFiles(); if (files == null) return; ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors()); for (File f : files) { executor.submit(() -> { if (f.isDirectory()) scan(f); else System.out.println(f.getAbsolutePath()); }); } executor.shutdown(); } public static void main(String[] args) { File root = new File("..."); // 替换为要扫描的目录 scan(root); } }
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