Dark Horse Programmer ———— Java Base exception handling

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1. Architecture
Java.lang.Object
|----java.lang.Throwable
|-------java.lang.Error: errors, Java programs do nothing about this, do not explicitly handle
|-------java.lang.Exception: Exception. Need to be processed
|------runtimeexception: Run-time exception
|-----arrayindexoutofboundsexception/nullpointerexception/arithmeticexception/classcastexception
|------non-runtimeexception: compile-time exception

2. Because Java programs are divided into Javac.exe and java.exe two processes, exceptions can occur in each process. It is divided into compile-time exception, run-time exception
2.1 is common for run-time exceptions and can be handled without explicit processing.
2.2 For compile-time exceptions, you must explicitly handle
Compile-time exception, not to say that there is an exception to deal with, but there is a hidden danger, must be in the compilation, prompt program, in case of an exception, how to deal with!

2. How do I handle exceptions?
"Scratch-and-throw model" in Java
* 1. " Throw ": When we execute the code, when an exception occurs, an object of the corresponding exception type is generated at the code of the exception and
* throws this object. (Auto throw/manual throw)
* > Once the object of this exception class is thrown, the program terminates execution
* > The object of this exception class is thrown to the caller of the method.
* 2. " Catch ": Catch the object of the exception class thrown out of the previous step. How to catch? That is, the way the exception is handled
* Java provides two ways to handle an object of an exception class.
* The way of processing one:

try{    //Possible exception code     }catch (Exception1 E1) {     //Handling Way 1     }catch (Exception2 E2) {     //processed by 2     } finally{     //code that must be executed      }

　　

* Note: Variables declared in 1.try, similar to local variables, out of the try{} statement, cannot be called
* 2.finally is optional.
* Inside the 3.catch statement is the handling of the exception object:
* >getmessage (); Printstacktrace ();

* 4. There can be multiple catch statements, and the exception class object thrown in the try matches the type of the exception class in the catch, once it satisfies
* Executes the code in the catch. After execution, jump out of multiple catch statements
* 5. If the exception is handled, then the subsequent code continues to execute.
* 6. If multiple exception types in a catch are "side-by-side" relationships, you can either.
* If more than one exception type in a catch is a "containment" relationship, the subclass must be placed above the parent class for processing. otherwise error!
* 7.finally is stored in code that is bound to be executed, regardless of whether the exception is still unhandled in the try, catch, and if there is a return statement.
* 8.try-catch can be nested.
Treatment Method Two:
At the declaration of the method, use the throws + exception type explicitly

public void Method1 ()  throws Exception1 E1,exception2 e2{//possible exception (especially compile-time exception, must be handled)     } public        void Method2 () Throws Exception1 E1,exception2 e2{method1 ();    }     public void Method3 () {try{method2 ();} catch (Exception1 E1) {System.out.println (E1.getmessage ());    } catch (Exception2 E2) {System.out.println (E2.getmessage ());    }     }   public static void Main (string[] args) {object 1.method3 ();//The above Exception1 and Exception2 exceptions will not appear again!   }

　　

3. How do I manually throw an exception?
Inside the method, you can use the Throw + Exception class object to manually throw an exception!

Compares the size of a radius of two circles. public int compareTo (Object obj) throws exception{if (this = = obj) {return 0;} else if (obj instanceof circle) {Circle c = (circle) obj;if (This.radius > C.radius) {return 1;} else if (This.radius = = C.radius) {return 0;} else{return-1;}} else{//return-2;//manually throws an exception//throw new Exception ("The incoming type is wrong!") ");//throw new String (" The incoming type is wrong! "); throw new MyException (" The incoming type is wrong! ") ");}}

　　

4. How do I customize an exception class?
> Throws an exception manually, in addition to throwing an object out of the exception class that is out of the box, you can also throw an object with a custom exception class!
> How do I customize an exception class?

public class MyException extends exception{static final long serialversionuid = -70348975766939l;public myexception () {} Public myexception (String msg) {super (MSG);}}

　　

Dark Horse Programmer ———— Java Base exception handling