关于java异常处理执行路径的问题

[不愿透露姓名的高杨童鞋]

Thinking in Java 12章的一个例子. 刚开始看到的现象跟预期的不一样,我稍微改了一下.

class MyException2 extends Exception{
	private int x;
	public MyException2(){
		super();
	}
	public MyException2(String msg){
		super(msg);
	}
	public MyException2(String msg,int x){
		super(msg);
		this.x = x;
	}
	public int val(){
		return x;
	}
	public String getMessage(){
		return "Detail Message: "+x+" "+super.getMessage();
	}
}
public class ExtralFeature {
	public static void f() throws MyException2{
		System.out.println("Throwing MyExcetion2 from f()");
		throw new MyException2();
	} 
	public static void g() throws MyException2{
		System.out.println("Throwing MyExcetion2 from g()");
		throw new MyException2("Originated in g()");
	} 
	public static void h() throws MyException2{
		System.out.println("Throwing MyExcetion2 from h()");
		throw new MyException2("Originated in h()",47);
	} 
	
	public static void main(String[] args) {
		for(int i=0;i<5;i++){
			try {
				f();
			} catch (MyException2 e) {
				// TODO: handle exception
				e.printStackTrace();
			}
			try {
				g();
			} catch (MyException2 e) {
				// TODO: handle exception
				e.printStackTrace();
			}
			
			try {
				h();
			} catch (MyException2 e) {
				// TODO: handle exception
				e.printStackTrace();
				System.out.println("e.val="+e.val());
			}
			System.out.println("========================================");
		}
	}
}

我的理解,mian方法中,执行到f()方法的时候,抛出异常,程序暂停,进入catch块中去处理. 完事儿之后返回,继续往下执行下一个try块中的g()方法,g()方法抛出异常之后,进入g()方法的catch块处理...
打印的结果应该是:

引用

Throwing MyExcetion2 from f()
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
Throwing MyExcetion2 from g()
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
Throwing MyExcetion2 from h()
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
e.val=47
========================================
Throwing MyExcetion2 from f()
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
Throwing MyExcetion2 from g()
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
Throwing MyExcetion2 from h()
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
e.val=47
========================================
Throwing MyExcetion2 from f()
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
Throwing MyExcetion2 from g()
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
Throwing MyExcetion2 from h()
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
e.val=47
========================================
Throwing MyExcetion2 from f()
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
Throwing MyExcetion2 from g()
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
Throwing MyExcetion2 from h()
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
e.val=47
========================================
Throwing MyExcetion2 from f()
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
Throwing MyExcetion2 from g()
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
Throwing MyExcetion2 from h()
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
e.val=47
========================================

但是正常执行的时候可能是这个样子:

引用

Throwing MyExcetion2 from f()
Throwing MyExcetion2 from g()
Throwing MyExcetion2 from h()
e.val=47
========================================
Throwing MyExcetion2 from f()
Throwing MyExcetion2 from g()
Throwing MyExcetion2 from h()
e.val=47
========================================
Throwing MyExcetion2 from f()
Throwing MyExcetion2 from g()
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
Throwing MyExcetion2 from h()
e.val=47
========================================
Throwing MyExcetion2 from f()
Throwing MyExcetion2 from g()
Throwing MyExcetion2 from h()
e.val=47
========================================
Throwing MyExcetion2 from f()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
ch12_Exception.MyException2: Detail Message: 0 null
at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39)
ch12_Exception.MyException2: Detail Message: 0 Originated in g()
at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45)
ch12_Exception.MyException2: Detail Message: 47 Originated in h()
at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33)
at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52)
Throwing MyExcetion2 from g()
Throwing MyExcetion2 from h()
e.val=47
========================================

看上去好像在多线程执行一样. 刚学java,不是很懂. 是我理解错了吗? 还是说正确的应该是,main线程一直在执行,遇到f()方法抛出异常,将catch块交给另外一个线程,然后main这个线程会继续往下执行.

[unauthorized401]

1楼正解。。。

[不愿透露姓名的高杨童鞋]

引用 1 楼 abcdefghiijklmnopqrs 的回复:

不是多线程的问题,只有单线程,只不过System.out.println()这个方法输出到控制台时是用BufferedWriter实现的,这个输出流是带有缓冲区的,所以你调用了println这个方法只是先写入到缓冲区中,并没有打印到控制台上而e.printStackTrace()这个方法的输入是有PrintStream来完成的,没有缓冲区

是的哦,把它改成,e.printStackTrace(System.out);都输出到System.out流中结果就对上了. 多谢.

[abcdefghiijklmnopqrs]

不是多线程的问题,只有单线程,只不过System.out.println()这个方法输出到控制台时是用BufferedWriter实现的,这个输出流是带有缓冲区的,所以你调用了println这个方法只是先写入到缓冲区中,并没有打印到控制台上而e.printStackTrace()这个方法的输入是有PrintStream来完成的,没有缓冲区

[尼古拉斯-全蛋]

楼上说的有道理