try/catch/finally的各种情况

众所周知，try语句报错，会执行catch语句，然后执行finally，以下这几种情况，看看会如何输出。

1、try语句中包含return，finally包含输出语句

public static void main(String[] args) {
	// write your code here
        System.out.println(get());
}
 
public static String get(){
    try {
        return "111";
    } catch (Exception e) {
        throw new NullPointerException();
    } finally {
        System.out.println(123);
    }
 }

结果：finally正常输出

 2、try语句报错，catch语句抛出错误，finally包含输出语句

public static void main(String[] args) {
	// write your code here
        System.out.println(get());
}
 
public static String get(){
   try {
    	throw new NullPointerException();
	} catch (Exception e) {
 		throw new NullPointerException();
	} finally {
		System.out.println(123);
    }
}

结果：finally执行成功，再抛出catch中的错误

 3、try语句报错，catch包含return，finally包含输出语句

public static void main(String[] args) {
	// write your code here
        System.out.println(get());
}
 
public static String get(){
    try {
        throw new NullPointerException();
    } catch (Exception e) {
        System.out.println(111);
        return "456";
    } finally {
        System.out.println(123);
    }
}

结果：catch中的语句输出成功，finally中的语句输出成功

 4、try和finally中的语句都包含输出

public static void main(String[] args) {
	// write your code here
    System.out.println(get());
}
 
public static String get(){
    try {
        return "123";
    } catch (Exception e) {
        System.out.println(111);
        return "456";
    } finally {
        return "789";
    }
}

结果：finally成功return

 5、try报错，catch和finally包含return语句

public static void main(String[] args) {
	// write your code here
    System.out.println(get());
}
 
public static String get(){
    try {
        throw new NullPointerException();
    } catch (Exception e) {
        System.out.println(111);
        return "456";
    } finally {
        return "789";
    }
}

结果：finally成功return

 6、try包含return，finally抛出错误

    public static void main(String[] args) {
	// write your code here
        System.out.println(get());
    }
 
    public static String get(){
        try {
            return "789";
 
        } catch (Exception e) {
            System.out.println(111);
            return "456";
        } finally {
            throw new NullPointerException();
        }
    }

结果：直接报错

 7、try包含报错，catch包含return，finally抛出错误

public static void main(String[] args) {
	// write your code here
    System.out.println(get());
}
 
public static String get(){
    try {
        throw new RuntimeException();
    } catch (Exception e) {
        return "456";
    } finally {
        throw new NullPointerException();
    }
}

结果：直接报错

通过上面的例子，我们可以得到以下结论：

1. finally语句存在的话，一定会执行
2. 若try语句报错，会执行catch语句，如果catch语句也报错，则会先执行finally语句，再抛出catch的错误
3. try语句或者catch语句return了，finally仍然会执行
4. 若finally语句中包含return，则会覆盖try或者catch中的return
5. 若finally语句报错，这个错误一定会抛出，终止程序