Error, Exception and Its types

Error Vs. Exception

• Error: An Error “indicates serious problems that a reasonable application should not try to catch.”
• Exceptions : An Exception “indicates conditions that a reasonable application might want to catch.”

• There are three types of Errors in Java.
• 1.Compile-time errors.
• 2. Run time errors.
• 3.Logical errors.
  
  

Compile-time errors.

• Errors that occur during compiling the program.
• Example:
• missing a semicolon at the end of a statement
• missing braces
• class not found
• These errors will be detected by java compiler and displays the error.
• Full Example:

class CompileTimeDemo
{
public static void main(String args[])
{
int i=10;
//Missing semicolon at the end of statement
System.out.println(i)
}
}

Run time errors.

• Run Time errors are occurs during execution of program. 
• Java compiler will not detect Run Time errors.
• These are detected by the JVM while the program is running.
• Full Example:

class  RunTimeErrorDemo
{
public static void main(String args[])
{
int arr[] = new int[4];
arr[5] = 100;
System.out.println("Success");
}
}

Logical errors.

• Logical error means no errors during compile & run time but not proper output. 
• It will not be detected by a compiler nor by the JVM. 
• Errors may be generate due to wrong idea or concept used by a programmer while coding.
• Full Example:

class  LogicalErrorDemo
{
public static void main(String args[])
{
int i = Integer.parseInt("Hello");
System.out.println(i);
}
}

Exception:

• Exception is a runtime error which can be handled or prevented.
• It appears during the execution of the program. 
• There two types of exceptions:
• 1. Checked Exception (also called Compile time exception)
• The exceptions can be detected by java compiler while compiling are called checked exceptions.
• 2. Unchecked Exception (also called Run time exception)
• The exception detected by JVM during runtime is called unchecked exceptions.
• Full Example:

class RunTimeErrorDemo{
public static void main(String args[])
{
try
{
int arr[] = new int[4];
arr[5] = 100;
}
catch(Exception e)
{
System.out.println(e);
}
System.out.println("Success");
}
}

Exception Class:

• Both Errors and Exceptions are the subclasses of java.lang.Throwable class.
• Throwable is a class in java.lang package.
• It is represents all errors and exceptions.
• It surely cause termination of the program abnormally.

Error Vs. Exceptions:

• Recovering from Error is not possible.
• We can recover from exceptions by either using try-catch block or throwing exceptions back to caller.

• All errors in java are unchecked type.
• Exceptions include both checked as well as unchecked type.

• Errors are mostly caused by the environment in which the program is running.
• The program itself is responsible for causing exceptions.

• Errors occur at runtime and not known to the compiler.
• All exceptions occur at runtime but checked exceptions are known to the compiler while unchecked are not.

• They are defined in java.lang.Error package.
• They are defined in java.lang.Exception package

• Examples: java.lang.StackOverflowError, java.lang.OutOfMemoryError
• Examples: 
• Checked Exceptions: SQLException, IOException
• Unchecked Exceptions : ArrayIndexOutOfBoundException, NullPointerException, ArithmeticException.