0x00 Preface

What is anomaly?

The event that causes the normal flow of a program to be interrupted is called an exception.

content

1.try catch

0x01 try catch

How to use: try catch contains content
Note: the program can continue to run without interruption

Raise a chestnut.

package first;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;

public class Demo {
    public static void main(String[] args) {
        File f=new File("d:/123456798.exe");
        try{
            new FileInputStream(f);
            System.out.println("Successfully opened");
        }catch(FileNotFoundException e)
        {
            System.out.println("file does not exist");

        }
    }
}

A reference to a subclass.

Another chestnut

package first;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;

public class Demo {
    public static void main(String[] args) {
        File f=new File("d:/123456798.exe");
        try{
            new FileInputStream(f);
            System.out.println("Successfully opened");
        }catch(Exception e)
        {
            System.out.println("file does not exist");

        }
    }
}

Reference to the parent class.

0x02 catch multiple exceptions

1. Capture separately

2. Capture together

package first;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class Demo {
    public static void main(String[] args) {
        File f=new File("d:/123456798.exe");
        try{
            new FileInputStream(f);
            System.out.println("Successfully opened");
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            Date d = sdf.parse("2018-03-28");
        }catch(FileNotFoundException | ParseException e)
        {
             if (e instanceof FileNotFoundException)
                    System.out.println("file does not exist");
                if (e instanceof ParseException)
                    System.out.println("Date format parsing error");
        }
    }
}

0x03 final

Code in finally is executed, no matter what happens.

Raise a chestnut.

package first;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class Demo {
    public static void main(String[] args) {
        File f=new File("d:/123456798.exe");
        try{
            new FileInputStream(f);
            System.out.println("Successfully opened");
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            Date d = sdf.parse("2018-03-28");
        }catch(FileNotFoundException | ParseException e)
        {
             if (e instanceof FileNotFoundException)
                    System.out.println("file does not exist");
                if (e instanceof ParseException)
                    System.out.println("Date format parsing error");
        }finally{
            System.out.println("No matter what happens, I will do it!");
        }
    }
}

Effect

0x04 exception classification

1. Exceptions
2. Abnormal operation
3. mistake

1. Exceptions

An exception that must be handled. try catch, or throw out.

2. Abnormal operation

An exception that does not require a try catch.

Common operation exception: divisor is not 0
Subscript boundary crossing
Null pointer exception

3. mistake

System level exception, usually out of memory.