可以给线程指定异常处理类来捕获异常进行自定义处理。线程中的异常可通过线程组异常处理来实现异常传递，线程组 ThreadGroup 实现了 Thread.UncaughtExceptionHandler 接口。

异常处理
在 Java 多线程技术中，可以对多线程中的异常进行捕捉，使用的是 UncaughtExceptionHandler 类，可以对发生的异常进行有效的处理。
1.创建线程

public class MyThread extends Thread {
   // 堆代码 duidaima.com
    @Override
    public void run() {
        String username = null;
        System.out.println(username.hashCode());
    }
}

2.线程异常处理测试

public class MainCatchException {
    public static void main(String[] args) {

        MyThread t1 = new MyThread();
        t1.setName("线程t1");
        t1.start();

        MyThread t2 = new MyThread();
        t2.setName("线程t2");
        t2.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            @Override
            public void uncaughtException(Thread t2, Throwable e) {
                System.out.println("线程：" + t2.getName() + " 出现了异常");
                e.printStackTrace();
            }
        });
        t2.start();

        MyThread t3 = new MyThread();
        t3.setName("线程t3");
        t3.start();

        MyThread t4 = new MyThread();
        MyThread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            @Override
            public void uncaughtException(Thread t4, Throwable e) {
                System.out.println("默认线程异常处理：" + t4.getName());
                e.printStackTrace();
            }
        });
        t4.setName("线程t4");
        t4.start();
    }
}

异常传递
Java 的线程组实现了 Thread.UncaughtExceptionHandler 接口，在使用线程组时，可以重写 void uncaughtException(Thread t, Throwable e) 方法，使异常可以在线程组中的线程传递，即其中一个线程异常，线程组中的线程都会抛出此异常。
1.创建线程

public class MyThread extends Thread {

    private String num = "a";

    public MyThread() {
        super();
    }

    public MyThread(ThreadGroup threadGroup, String name) {
        super(threadGroup, name);
    }

    @Override
    public void run() {
        int numInt = Integer.parseInt(num);
        System.out.println("在线程中打印：" + (numInt + 1));
    }
}

2.线程组

public class MyThreadGroup extends ThreadGroup {
   // 堆代码 duidaima.com
    public MyThreadGroup(String name) {
        super(name);
    }

    @Override
    public void uncaughtException(Thread t, Throwable e) {
        super.uncaughtException(t, e);
        System.out.println("线程组的异常处理");
        e.printStackTrace();
    }
}

3.自定义异常处理类

public class ObjectUncaughtExceptionHandler implements Thread.UncaughtExceptionHandler {
    @Override
    public void uncaughtException(Thread t, Throwable e) {
        System.out.println("对象的异常处理");
        e.printStackTrace();
    }
}

public class StateUncaughtExceptionHandler implements Thread.UncaughtExceptionHandler {
    @Override
    public void uncaughtException(Thread t, Throwable e) {
        System.out.println("静态的异常处理");
        e.printStackTrace();
    }
}

4. Main 测试类

public class MainTest {

    public static void main(String[] args) {
        MyThreadGroup group = new MyThreadGroup("我的线程组");
        MyThread myThread1 = new MyThread(group, "我的线程1");
        MyThread myThread2 = new MyThread(group, "我的线程2");

//        myThread.setUncaughtExceptionHandler(new ObjectUncaughtExceptionHandler());
//        MyThread.setDefaultUncaughtExceptionHandler(new StateUncaughtExceptionHandler());

        myThread1.start();
        myThread2.start();
    }
}

5.运行输出结果

线程组的异常处理
线程组的异常处理
Exception in thread "我的线程2" Exception in thread "我的线程1" java.lang.NumberFormatException: For input string: "a"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at com.java.jdk.thread.exception.Demo1.MyThread.run(MyThread.java:17)
java.lang.NumberFormatException: For input string: "a"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at com.java.jdk.thread.exception.Demo1.MyThread.run(MyThread.java:17)
java.lang.NumberFormatException: For input string: "a"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at com.java.jdk.thread.exception.Demo1.MyThread.run(MyThread.java:17)
java.lang.NumberFormatException: For input string: "a"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at com.java.jdk.thread.exception.Demo1.MyThread.run(MyThread.java:17)