00 start() & run() 代码展示

import org.apache.log4j.Logger;
/**
 * @ClassName StartAndRun
 * @Description TODO
 * @Author wenqing_liu
 * @Date 2021/5/30 21:07
 */
public class StartAndRun {
    private final Logger logger = Logger.getLogger(this.getClass());
    public void runMethod() {
        Thread t1 = new Thread("t1") {
            @Override
            public void run() {
                logger.info("Thread Running...");
            }
        };
        t1.run();
        logger.info("Main Thread Running...");
    }
    public void startMethod() {
        Thread t1 = new Thread("t1") {
            @Override
            public void run() {
                logger.info("Thread Running...");
            }
        };
        t1.start();
        logger.info("Main Thread Running...");
    }
}

测试代码

import org.junit.jupiter.api.Test;
/**
 * @ClassName StartAndRunTest
 * @Description TODO
 * @Author wenqing_liu
 * @Date 2021/5/30 21:10
 */
class StartAndRunTest {
    @Test
    void testStartMethod() {
        StartAndRun sr = new StartAndRun();
        sr.startMethod();
    }
    @Test
    void testRunMethod() {
        StartAndRun sr = new StartAndRun();
        sr.runMethod();
    }
}

01 run()

[Test worker] 21:19:56.369 INFO  methods.StartAndRun:18 - Thread Running...
[Test worker] 21:19:56.373 INFO  methods.StartAndRun:23 - Main Thread Running...

从上面的运行日志可以看出，日志打印的线程都是 [Test worker] ，可见方法调用还是同步的，

02 start()

[Test worker] 21:32:00.340 INFO  methods.StartAndRun:35 - Main Thread Running...
[t1] 21:32:00.340 INFO  methods.StartAndRun:30 - Thread Running...

运行测试方法 testStartMethod() ，调用 start() 方法后，日志打印的线程有 [Test worker], [t1] , 方法的调用是异步的。

03 小结

• 直接调用 run() 方法，并没有启动新的线程
• 使用 start() 是启用新的线程，通过新的线程执行 run() 中的方法