Question

In Java, how a compiler will identify that there is a checked exception? I mean how it is identifying it?

Answer 1

Right from the docs:

A compiler for the Java programming language checks, at compile time,
that a program contains handlers for checked exceptions, by analyzing
which checked exceptions can result from execution of a method or
constructor. For each checked exception which is a possible result,
the throws clause for the method (§8.4.6) or constructor (§8.8.5) must
mention the class of that exception or one of the superclasses of the
class of that exception. This compile-time checking for the presence
of exception handlers is designed to reduce the number of exceptions
which are not properly handled.

The unchecked exceptions classes are the class RuntimeException and
its subclasses, and the class Error and its subclasses. All other
exception classes are checked exception classes. The Java API defines
a number of exception classes, both checked and unchecked. Additional
exception classes, both checked and unchecked, may be declared by
programmers. See §11.5 for a description of the exception class
hierarchy and some of the exception classes defined by the Java API
and Java virtual machine.

So basically it looks at the code, if it comes across an exception, looks up the inheritance hierarchy of the exception to decide if it is checked or unchecked.

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