when i search this on google then it show that error means compile time error and exception is runtime error? but i think that it is not that so....

CodePudding user response：

That is generally correct. Although the terms are colloquially interchangeable in many domains.

An Error, also known as a compile-time error, is a statement of fact. (Or NOT fact) The compiler is unable to compile the output.

• Technically an error is a state in code that has raised an exception in the compiler's runtime :)

An Exception is raised at runtime and is the result of an exceptional combination of values.

Because an Exception is raised at runtime, we can generally write code to catch and handle or workaround an exception within your script or code. An Error prevents the code from being compiled and thus executed at all, so our only option is to modify the code to resolve an Error.

A compiler may perform syntax and sometimes type checking to ensure that the code follows a set of pre-determined rules and can be compiled into executable statements, but it is not until invalid values are passed into those statements that an Exception can occur, that is harder for a compiler to do and so is generally only detected at Runtime.

Some advanced or specialised compilers may perform checks against common values and as a programer you can write unit tests to try and pre-emptively detect exceptions before releasing your code.

CodePudding user response：

An Error "indicates serious problems that a reasonable application should not try to catch."

while

An Exception "indicates conditions that a reasonable application might want to catch."

Error along with RuntimeException & their subclasses are unchecked exceptions. All other Exception classes are checked exceptions.

Checked exceptions are generally those from which a program can recover & it might be a good idea to recover from such exceptions programmatically. Examples include FileNotFoundException, ParseException, etc. A programmer is expected to check for these exceptions by using the try-catch block or throw it back to the caller

On the other hand we have unchecked exceptions. These are those exceptions that might not happen if everything is in order, but they do occur. Examples include ArrayIndexOutOfBoundException, ClassCastException, etc. Many applications will use try-catch or throws clause for RuntimeExceptions & their subclasses but from the language perspective it is not required to do so. Do note that recovery from a RuntimeException is generally possible but the guys who designed the class/exception deemed it unnecessary for the end programmer to check for such exceptions.

Errors are also unchecked exception & the programmer is not required to do anything with these. In fact it is a bad idea to use a try-catch clause for Errors. Most often, recovery from an Error is not possible & the program should be allowed to terminate. Examples include OutOfMemoryError, StackOverflowError, etc.

Do note that although Errors are unchecked exceptions, we shouldn't try to deal with them, but it is ok to deal with RuntimeExceptions(also unchecked exceptions) in code. Checked exceptions should be handled by the code.