Java多线程并发常见问题示例

原创桃扇骨 2024-09-16 02:30 100阅读 0赞

在Java多线程并发编程中，常见的问题包括：

1. 线程安全：多个线程同时访问共享资源可能导致数据不一致。如例：
   ```java
   public class Counter {
       private int count = 0;

public synchronized void increment() {
           count++;
           notifyAll();
       }

public synchronized int decrement() {
           if (count > 0) {
               count--;
               notifyAll();
               return count;
           } else {
               throw new IllegalArgumentException("Count is already zero");
           }
       }

public synchronized int getCount() {
           return count;
       }
   }
   ```
   
2. 死锁：多个线程相互等待对方释放资源导致死锁。如例：
   ```java
   class BankAccount {
       private String accountNumber;
       private double balance;

// ... getters and setters ...
    }

class BankService {
       private List<BankAccount> accounts;

// ... constructor, addAccount method ...
    }
   
    // ... create BankService and BankAccounts ...
    
    new Thread(() -> {
        BankService service = ...; // get the service
        BankAccount account1 = ...; // create or get an account
        BankAccount account2 = ...; // create or get another account

service.addAccount(account1);
        service.addAccount(account2);

while (true) {
            if (account1.balance >= 100 && account2.balance <= 50) {
                service.removeAccount(account2);
                break;
            }
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }).start();
   ```
   
3. 线程优先级问题：Java默认所有线程平等，但有时需要根据业务需求设置线程优先级。如例：
   ```java
   // 创建两个具有不同优先级的线程
   Thread thread1 = new Thread(new Runnable() {
       @Override
       public void run() {
           System.out.println("Thread 1: Priority " + thread1.getPriority());
       }
   })));
   
   Thread thread2 = new Thread(new Runnable() {
       @Override
       public void run() {
           System.out.println("Thread 2: Priority " + thread2.getPriority()));
       }
   })));
   
   // 设置线程优先级
   thread1.setPriority(1); // 优先级高于默认值（5）
   thread2.setPriority(2); // 优先级低于默认值（5）

// 启动线程
   thread1.start();
   thread2.start();
   ```
   
希望以上的示例能帮助你理解Java多线程并发中的常见问题。