Custom exception classes and exercises

Custom exception classes

Java The provided exception class is not enough , You need to define . Format ：

public class XXXException extends  Exception / RuntimeException{
		 Add a null parameter constructor ;
		 Add a constructor with exception information ;
}

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Be careful ：1. The custom exception class is generally in the form of Exception ending , This class is an exception class . 2. Custom exception classes , Must inherit Exception perhaps RuntimeException Inherit Exception： The custom exception class is a compile time exception , If a compile time exception is thrown inside the method , You have to deal with this exception throws perhaps try/catch Inherit RuntimeException： Abnormal operation period , Can be either , Give to virtual machine .

practice ：

Simulated user registration exception , If the user name already exists , Throw an exception , And prompt . analysis ： 1. Use the array to save the registered user name （ database ） 2. Use scanner Get the user name entered by the user （ Front page ） 3. Define a method , Judge the user name entered by the user Traverse the stored user name , Get each user name for comparison ture： User name exists ： Throw out regiserException abnormal , And said “ Hello , The user name has been registered ”. false： Continue to traverse and compare If the cycle is over , Not yet ： congratulations , Registered successfully . Next, define the main method ：

Define method judge method ：

Call the method in the main method ：

Remember to throw exceptions when writing . If you use try/catch Remember to add one return, The ending method , Otherwise, the following code still executes .