Assertion Error In Java Example
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Uses Of Assertions In Java
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Java Assertion Error Vs Exception
Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up What is what is assertion error in java an AssertionError? In which case should I throw it from my own code? up vote 24 down vote favorite 5 In Item 2 of the "Effective Java, 2nd edition" book, there is this snippet of code, in which the author wants to forbid the empty initialization of an object. class Example { private Example() { throw new AssertionError(); } } The type of exception thrown, assertion error junit is what confuses me here. I don't understand if the AssertionError is thrown just because of an absence of more suited errors or because it should be this way. As I understand, this error is thrown by the framework when an assert statement fails. Also, in the javadoc it's just written [An AssertionError is] Thrown to indicate that an assertion has failed. But I don't see any assertion (true-false statement) being violated here. Of course the "You shall not instantiate an item of this class" statement has been violated, but if this is the logic behind that, then we should all throw AssertionErrors everywhere, and that is obviously not what happens. FWIW, I'd have just thrown a new IllegalStateException("Must not instantiate an element of this class") Is there something wrong with that? In which case should I throw an AssertionError in my own code? Sorry if it's just a subtle doubt but I use this pattern a lot in my code and I want to make sure I'm doing the right thing. java exception effective-java share|improve this question edited Jul 21 '14 at 11:03 asked Jul 21 '14 at 10:43 d
a statement in the JavaTM programming language that enables you to test your assumptions about your program. For example, if you write
Java.lang.assertionerror Junit
a method that calculates the speed of a particle, you might how to handle assertion error in java assert that the calculated speed is less than the speed of light. Each assertion contains a
Java.lang.assertionerror Null
boolean expression that you believe will be true when the assertion executes. If it is not true, the system will throw an error. By verifying that the http://stackoverflow.com/questions/24863185/what-is-an-assertionerror-in-which-case-should-i-throw-it-from-my-own-code boolean expression is indeed true, the assertion confirms your assumptions about the behavior of your program, increasing your confidence that the program is free of errors. Experience has shown that writing assertions while programming is one of the quickest and most effective ways to detect and correct bugs. As an added benefit, assertions serve http://docs.oracle.com/javase/7/docs/technotes/guides/language/assert.html to document the inner workings of your program, enhancing maintainability. This document shows you how to program with assertions. It covers the topics: Introduction Putting Assertions Into Your Code Compiling Files That Use Assertions Enabling and Disabling Assertions Compatibility With Existing Programs Design FAQ Introduction The assertion statement has two forms. The first, simpler form is: assert Expression1 ; where Expression1 is a boolean expression. When the system runs the assertion, it evaluates Expression1 and if it is false throws an AssertionError with no detail message. The second form of the assertion statement is: assert Expression1 : Expression2 ; where: Expression1 is a boolean expression. Expression2 is an expression that has a value. (It cannot be an invocation of a method that is declared void.) Use this version of the assert statement to provide a detail message for the AssertionError. The system passes the value of Expression2 to the appropriate AssertionError constructor, which uses the string representation of the
how assertions differs from Exception handling technique.We all know about how assertions works.But anyway,Let's have a glance at assertions to know its http://craftingjava.blogspot.com/2012/07/javalangassertionerror.html advantage. Assertions are used to evaluate a condition.If the condition gets failed then they will throw java.lang.Assertion error. Usage of Assertions: 1.assert a!=null; This statement will check whether 'a' is http://onebigfunction.com/blog/2015/11/16/assert-vs-assertionerror/ null or not.If 'a' is null then this statement will throw an Assertion error.you could have thought of throwing an NullPointerException and processing it using the try and catch block rather assertion error than using the Assertion error. But one of the great advantage of assertions when compared to exception handling is that assertions allows us to use condition checks during testing and automatically removes thestatements from the generated code thereby not affecting the execution speed. If you have lot of conditions to be checked in your program and have implemented exception handling techniques for assertion error in violation of conditions,then this will slower the program execution. I have shown this slowering of the program execution, using the two programs that i have included in this post. When do we need this Assertion? Note that the assertion should be used to deal with unrecoverable errors or errors that will disrupt operation of the entire program.Mostly it will not be used to deal withrecoverable conditions. one of the most common example where assertion can be used is explained through the sorting program.In the sorting program it would be used tocheck the validity of parameters passed. If we want to sort an array of elements then before sorting it we should ensure that the array is not null.For this case assertion can be used.If an assertion error occurs then we can terminate the program rather than applying the sorting operations on that array. The two different implementations of the sorting program that throws assertion error and also an other program which throws NullPointerException is given below. program 1: ------------ class Desc1 { public void sort(int[] a) { int t; for(int j=0;j<=5;j++) { f
for a little while also. What's the difference between assert and AssertionError? People often ask what's the difference between assert and manually throwing an AssertionError given that an assert statement will throw the AssertionError anyway? Learning by Example Let's look at a super short example to paint a better picture: /** * Example 1: assert statement, this is a totally goofy example but bear with me. */ public class Test { public static void main(String[] args) { assert false; } } Compile and run javac Test.java && java Test You may (or may not) be surprised to see no output. This is because java is ignoring your assertions. Simply re-run your application with assertions enabled, using the -ea switch: java -ea Test Exception in thread "main" java.lang.AssertionError at Test.main(Test.java:3) Now let's try throwing an AssertionError manually and see what happens: /** * Example 2: Using AssertionError() */ public class Test { public static void main(String[] args) { throw new AssertionError(); } } Build & run: javac Test.java && java Test Exception in thread "main" java.lang.AssertionError at Test.main(Test.java:3) It seems like if we throw an AssertionError it guarantees that our program will crash. You might be wondering how that could possibly be a good thing, but first let me explain the semantics behind