Checked Exceptions vs UnChecked Exceptions - Java

Here is it with the image of Exception class hierarchy - [image courtesy: JavaTpoint].

There are 3 key class to remember - Throwable, Exception and Error in this hierarchy. Among these classes exception can be divided into two types - "Checked Exception" and "Unchecked Exception"

Checked Exception:

• The classes that extend Throwable class except RuntimeException and Error are known as checked exceptions.
• Also known as compile time exception because these type of exceptions are checked at compile time. That means if we ignore these exception (not handled with try/catch or throw the exception) then a compilation error occurred.
• They are programmatically recoverable problems which are caused by unexpected conditions outside control of code (e.g. database down, file I/O error, wrong input, etc)
• We can avoid them using try/catch block.
• Example: IOException, SQLException etc

Unchecked Exception:

• The classes that extend RuntimeException are known as unchecked exceptions
• Unchecked exceptions are not checked at compile-time rather they are checked at runtime.And thats why they are also called "Runtime Exception"
• They are also programmatically recoverable problems but unlike checked exception they are caused by faults in code flow or configuration.
• Example: ArithmeticException,NullPointerException, ArrayIndexOutOfBoundsException etc
• Since they are programming error, they can be avoided by nicely/wisely coding. For example "dividing by zero" occurs ArithmeticEceeption. We can avoid them by a simple if condition - if(divisor!=0). Similarly we can avoid NullPointerException by simply checking the references - if(object!=null) or using even better techniques

Error:

• Error refers irrecoverable situation that are not being handled by try/catch
• Example: OutOfMemoryError, VirtualMachineError, AssertionError etc.