ZJU-java advanced notes week 7 (exception handling)

1. Definition of exception
   

2. Catch exception example

try{
    
    
    //可能产生异常的代码
}catch(Type1 id1){
    
    
    //处理Type1异常的代码
}catch(Type2 id2){
    
    
    //处理Type2异常的代码
}catch(Type3 id3){
    
    
    //处理Type3异常的代码
        }

The significance of exception capture: the program does not need to be terminated when an exception occurs
3.

4. What can be done after the abnormal object is caught

1. String getMessage();
2. String toString();
3. void printStackTrace();

例
    public static void main(String[] args){
    
    

        try {
    
    
            k();
        }catch (ArrayIndexOutOfBoundsException e){
    
    
            System.out.println(e.getMessage());//放在异常对象里面的值
            System.out.println(e);//异常类的名字和它的message
            e.printStackTrace();//打印调用堆栈，显示调用关系及发生行号
        }
}

But it must not go back, and the specific processing logic depends on the needs of business logic

5. Throwing exceptions
   Add throw e; (Imperative sentence, throw) in catch{}.
   Effect: as if not caught

6. The exception statement is
   placed after the function that may throw an exception, as a statement, throws

    public static void readFile() throws OpenException{
    
    
        if(open() == -1){
    
    
            throw new OpenException();
        }
}

7. What can be "thrown out"?
   Any object that inherits the Throwable class
   Exception class inherits Throwable

8. Throwing subclass exceptions can be caught by the parent exception catcher
   Universal catcher-catch any exception

    catch(Exception e){
    
    
        System.out.println("Caught an exception");
}

9. There can be no more exceptions in the subclass than the parent class,
   but the exceptions that the parent class constructor will throw must be in the subclass constructor