java实现线程返回值

java实现线程返回值的方法有多种。其中一种方法是通过继承Thread类或者实现Runnable接口，在子线程中设置共享变量来获取返回值。这种方法的缺点是不能精确判断子线程是否执行完成。另一种方法是通过实现Callable接口，使用FutureTask启动子线程，然后使用FutureTask的get()方法获取返回值。这种方法可以精确地获取返回值。

以下是两种方法的示例代码：

方法一，通过设置共享变量获取返回值：

public class TestThread extends Thread {
    public String value = null;

    @Override
    public void run() {
        System.out.println("TestThread start....");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("TestThread end");
        value = "TestThread";
    }
}

public class Main {
    public static void main(String[] args) throws InterruptedException {
        TestThread thread = new TestThread();
        thread.start();
        while (thread.value == null) {
            Thread.sleep(100);
        }
        System.out.println(thread.value);
    }
}

方法二，使用Callable和FutureTask获取返回值：

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

public class TestCallable implements Callable<String> {
    @Override
    public String call() throws Exception {
        System.out.println("TestCallable start....");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("TestCallable end");
        return "TestCallable";
    }
}

public class Main {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        FutureTask<String> futureTask = new FutureTask<>(new TestCallable());
        Thread thread = new Thread(futureTask);
        thread.start();
        String value = futureTask.get();
        System.out.println(value);
    }
}