Concept and handling of exceptions

1、 Concept

   An exception is an instruction flow that causes a program to interrupt .
  Thowable Class is Java Superclass of all errors or exceptions in a language .

2、Throwable The classification of

Error：

error , deadly , Unrecoverable errors , Programmers are hard to deal with

Exception：

abnormal , Can handle , use Exception handling mechanism To deal with

There are two ways to deal with it ： Display processing (try{}catch(Exception){})
                             Do not display processing (throw,throws)

3、 Exception handling mechanism

        try{}catch(){}finally{}

Be careful ：

• Exception handling can only be from top to bottom, from fine to coarse , Not from thick to thin
• try catch finally The three cannot exist separately , But the three can coexist (try And catch,try And finally Can coexist )
• finally： Is the only exit as an exception handling mechanism

4、 Some common exceptions

• Arithmetical abnormality ( Divisor is 0):java.lang.ArithmeticException
• Number format conversion exception :
  java.lang.NumberFoematException
• Array out of bounds exception :
  java.lang.ArrayIndexOutOfBoundsException
• Null pointer exception :java.lang.NullPointerException
• Class conversion exception :java.lang.ClassCastException

import java.util.Scanner;
public class Test {
    
    public static void main(String[] args) {
    
        Scanner sc=new Scanner(System.in);
        try {
    
            System.out.println(" Please enter the first number ");
            String a = sc.next();
            int num1 = Integer.parseInt(a);
            System.out.println(" Please enter the second number ");
            String b = sc.next();
            int num2 = Integer.parseInt(b);
            int c = num1 / num2;
            System.out.println(" The result is ：" + c);
            Object obj=null;
            System.out.println(obj.hashCode());
            args=new String[2];
            System.out.println(args[3]);
        }catch(ArithmeticException e){
    
            System.out.println(" Arithmetical abnormality ");// if b The input is 0, There is an arithmetic exception 
        }catch(NumberFormatException e){
    
            e.printStackTrace();
            System.out.println(" Number format conversion exception ");// If the input is a non numeric character , Number format conversion exception occurs 
         }catch(ArrayIndexOutOfBoundsException e) {
    // The length printed exceeds the length of the array, and an array out of bounds exception occurs 
            e.printStackTrace();
        }catch(NullPointerException e){
    // If no object is specified, a null pointer exception will occur 
            e.printStackTrace();
            System.out.println(" Null pointer exception ");
        }catch(Exception e){
    
        e.printStackTrace();
        }finally{
    
        System.out.println(" No matter whether the program is abnormal or not , Always carry out .");
    }
        System.out.println(" end ");
    }
}