面试题与答案

An exception is an event that disrupts the normal flow of the program's instructions during runtime.

Example:

int result = 10 / 0; // This will throw an ArithmeticException

The 'finally' block is used to execute important code such as closing resources, whether an exception is thrown or not.

The 'throw' keyword is used to explicitly throw an exception.

Example:

throw new CustomException("This is a custom exception");

Yes, you can have a try block without a catch block if there is a finally block.

Example:

try { /* code */ } finally { /* cleanup code */ }

The 'NullPointerException' is thrown when attempting to access or modify an object reference that is null.

Example:

String str = null;
int length = str.length(); // This will throw NullPointerException

The 'try' block is used to enclose a block of code where exceptions might occur.

Example:

try { /* code that may throw exceptions */ } catch (Exception e) { /* handle exception */ }

'RuntimeException' is the superclass of those exceptions that can be thrown during the normal operation of the Java Virtual Machine.

'AssertionError' is thrown to indicate that an assertion has failed. It extends 'Error' class.

'Error' class represents serious errors that are not meant to be caught or handled by applications.

You can catch custom exceptions like any other exception by specifying the custom exception type in the catch block.

Example:

try { /* code */ } catch (CustomException ce) { /* handle custom exception */ }

'FileNotFoundException' is thrown when an attempt to open the file denoted by a specified pathname has failed.

Example:

try { FileReader fr = new FileReader("nonexistent.txt"); } 
catch (FileNotFoundException e) { /* handle file not found exception */ }

Checked exceptions are checked at compile-time, while unchecked exceptions are checked at runtime.

You can use multiple catch blocks or a catch block with multiple exception types separated by '|'.

Example:

try { /* code that may throw exceptions */ } catch (ExceptionType1 | ExceptionType2 e) { /* handle exception */ }

'try-with-resources' is a feature introduced in Java 7 to automatically close resources like files or sockets when they are no longer needed.

Example:

try (FileReader fr = new FileReader("file.txt")) { /* code that uses fr */ }

'Error' is thrown by the JVM and is not meant to be caught or handled, while 'Exception' is meant to be caught and handled.

The 'throws' clause is used to declare that a method may throw one or more types of exceptions. It is part of the method signature.

Example:

void myMethod() throws CustomException { /* method code */ }

'throw' is used to explicitly throw an exception, while 'throws' is used in method signature to declare that the method may throw one or more types of exceptions.

To create a custom exception, you need to extend the 'Exception' class or one of its subclasses.

Example:

class CustomException extends Exception { /* constructor and additional code */ }

No, there can be at most one 'finally' block associated with a 'try-catch' statement.

'System.exit(0)' terminates the Java Virtual Machine, while throwing an exception allows for a controlled termination of a specific part of the program.

'try-with-resources' simplifies resource management by automatically closing resources that are declared in the try statement. Resources must implement the 'AutoCloseable' interface.

Example:

try (BufferedReader br = new BufferedReader(new FileReader("file.txt"))) { /* code using br */ }

Yes, you can rethrow an exception by using the 'throw' statement without an argument inside a catch block.

Example:

catch (Exception e) { /* handling code */ throw e; }

'Error' is meant to indicate serious problems that should not be caught or handled, while 'RuntimeException' is a subclass of 'Exception' and represents exceptions that can be caught and handled.

'NullPointerException' occurs when you try to access or modify an object reference that is null. You can prevent it by checking for null before accessing the object.

Example:

if (obj != null) { /* code using obj */ }

Assertions are used to test assumptions about the program. They help in identifying logical errors during development and testing.

Example:

assert x > 0 : "x should be greater than 0";

In servlets, exceptions can be handled using the 'try-catch' block or by declaring them in the 'throws' clause of the method.

'finally' is used in exception handling to define a block of code that will be executed whether an exception is thrown or not. 'final' is a keyword used to apply restrictions on class, method, and variable.

Suppressed exceptions are exceptions that are not propagated up the call stack and are associated with try-with-resources. They are added to the primary exception as suppressed exceptions.

You can use try-catch blocks inside the run() method of a thread or implement the 'Thread.UncaughtExceptionHandler' interface.

'try' is used to enclose a block of code where exceptions might occur. 'catch' is used to handle exceptions. 'finally' is used to define a block of code that will be executed whether an exception is thrown or not. 'throw' is used to explicitly throw an exception.