How To Practise Custom Exception Inward Coffee - Tutorial Example

Sometimes nosotros require to produce custom Exception inward Java, i.e. Exceptions which are non defined inward JDK or whatever 3rd political party library your application is using. Though it’s widely recommended on several Exception best practices article, fifty-fifty Joshua Bloch has recommended inward Effective Java to prefer measure exception over custom exception, sometimes you lot truly require it. There are certainly guidelines to assist to detect whether you lot truly require a custom exception or not. You should write your ain exception classes if you lot response yeah to whatever of the next questions; otherwise, you lot tin belike purpose mortal else's.

•     Do you lot require an exception type that isn't represented yesteryear those inward the Java platform?
•     Would it assist users if they could differentiate your exceptions from those thrown yesteryear classes written yesteryear other vendors?
•     Does your code throw to a greater extent than than 1 related exception?
•     If you lot purpose mortal else's exceptions, volition users receive got access to those exceptions? The similar enquiry is, should your packet hold upward independent as well as self-contained?

Custom Exception or Custom Message alongside Standard Exception?

For event if you lot declare an Exception that doesn't furnish whatever useful information other than a custom cite hence it belike uses generic Exception cast alongside a custom message every bit shown inward below example:

public class DuplicateIDException extends Exception {}

This custom exception doesn't furnish whatever extra information e.g. choice ids, as well as that's why tin hold upward easily replaced yesteryear a custom message as well as measure Exception class, every bit shown below:

throw new Exception("ID already taken");

Even better, if you lot mean value the customer code is non going to convey whatever activity other than logging if the id is already taken, throw an unchecked exception:

throw new RuntimeException("ID already taken");

Checked or Unchecked?

Once you lot produce the determination to produce custom Exception, the adjacent affair is to determine on checked vs unchecked exception. As I said before, yesteryear default produce your exception unchecked as well as you lot volition detect it whether it should hold upward checked spell writing customer code. General guideline is to produce an exception unchecked if the customer code is non going to convey whatever activity other than logging.

How to produce Custom Exception inward Java - The Code

Here is our consummate code event of creating custom or user defined Exception inward Java.  In our example, nosotros receive got created NoSuchProductException, which is thrown yesteryear methods returning products. This is an unchecked Exception every bit nosotros made it inherit from RuntimeException. It inherit getMessage() method from Throwable as well as likewise has a method getProductId() which returns production id for which this exception has caused. Don't produce an Exception cast every bit nested class fifty-fifty if it's used exclusively yesteryear 1 class, ever declare Exceptions inward their ain class.

import java.util.HashMap; import java.util.Map;  /**  * Java Program to produce custom exception as well as examples to exhibit how to purpose  * custom exception inward Java.  *  * @author Javin Paul  */ public class CustomExceptionDemo {      private static final Map&lt;Integer, String&gt; products = new HashMap<>();      static {         products.put(100, "Coke");         products.put(101, "KitKat");         products.put(102, "Bisuits");         products.put(103, "Toast");     }      public static void main(String args[]) {         CustomExceptionDemo t = new CustomExceptionDemo();         t.getProduct(1000);     }      public String getProduct(int id) {         if (products.get(id) == null) {             throw new NoSuchProductException("No such production exists", id);         }         return products.get(id);     } }  class NoSuchProductException extends RuntimeException {      private int productId;      public NoSuchProductException() {         super();     }      public NoSuchProductException(String message, int productId) {         super(message);         this.productId = productId;     }      public NoSuchProductException(String message, int productId, Throwable cause) {         super(message, cause);         this.productId = productId;     }      @Override     public String toString() {         return super.toString();     }      @Override     public String getMessage() {         return super.getMessage() + " for productId :" + productId;     }      public int getProductId() {         return productId;     } }  Output: Exception inward thread "main" NoSuchProductException: No such production exists for productId :1000     at CustomExceptionDemo.getProduct(CustomExceptionDemo.java:26)     at CustomExceptionDemo.main(CustomExceptionDemo.java:21)

Things to recollect spell creating Custom Exception inward Java

Though creating a custom, exception is every bit tardily every bit subclassing java.lang.Exception class, at that spot are few best practices you lot tin follow to produce most of it. There is hence much criticism of checked exception due to boilerplate require to handgrip it, you lot volition hardly produce your custom exception every bit checked.

1) Don’t' purpose Exception to command application behavior. Exception treatment is real expensive every bit it requires native calls to re-create stack trace, each fourth dimension exception is created.

2) While creating a custom exception, prefer to produce an unchecked, Runtime exception than a checked exception, peculiarly if you lot know that customer is non going to convey whatever reactive activity other than logging.

3) If your custom exception is created yesteryear passing around other exception, hence ever comprise master copy Exception every bit a source; purpose constructor which takes Exception rather than exclusively message String.

4) Apart from providing default no declaration constructor on your custom Exception class, take in providing at to the lowest degree 2 to a greater extent than constructors, 1 which should receive got a failure message as well as other which tin receive got around other Throwable every bit the cause.

5) If possible, avoid creating custom Exception as well as re-use existing, measure Exception classes from JDK itself. Most of the fourth dimension you lot volition realize that all you lot require is a cast of IllegalArgumentException or ParseException or something similar.

6) While defining custom Exception, 1 of the most mutual error programmer produce is to mean value that constructor is inherited from java.lang.Exception class, for example, they mean value that their Exception cast volition automatically inherit default no declaration constructor as well as the 1 which takes a String message. This is non true. The constructor is non inherited inward Java, non fifty-fifty default constructor. It's truly added yesteryear the compiler rather than inherited from bring upward class. That's why I receive got declared 2 constructors, 1 alongside String parameter as well as other every bit Throwable parameter:

public NoSuchProductException(String message, int productId) {         super(message);         this.productId = productId;     }      public NoSuchProductException(String message, int productId, Throwable cause) {         super(message, cause);         this.productId = productId;     }
 

This is truly the measure means of creating custom Exception inward Java. In fellowship to salve time, you lot tin fifty-fifty produce a template of higher upward cast inward Eclipse IDE.

7) For readable code, it's proficient exercise to append the string Exception to the names of all classes that inherits (directly or indirectly) from the Exception cast e.g. instead of naming your cast IncorrectPassword, cite it IncorrectPasswordException.


That's all virtually How to produce custom Exception classes inward Java. As I said, outset seek to avoid the temptation of creating a produce novel Exception class, mean value if you lot tin reuse existing ones. If you lot absolutely need, hence produce certainly to follow best practices. At the bare minimum, produce an endeavor to produce unchecked exception rather than a checked one.

Further Learning
Complete Java Masterclass
Java Fundamentals: The Java Language
Java In-Depth: Become a Complete Java Engineer!

Bagikan Artikel ini