The Exception Handling in Java is one of the powerful mechanism to handle the runtime errors so that normal flow of the application can be maintained.
In this page, we will learn about Java exceptions, its type and the difference between checked and unchecked exceptions.
Dictionary Meaning: Exception is an abnormal condition.
In Java, an exception is an event that disrupts the normal flow of the program. It is an object which is thrown at runtime.
Exception Handling is a mechanism to handle runtime errors such as ClassNotFoundException, IOException, SQLException, RemoteException, etc.
The core advantage of exception handling is to maintain the normal flow of the application. An exception normally disrupts the normal flow of the application that is why we use exception handling. Let's take a scenario:
statement 1; statement 2; statement 3; statement 4; statement 5;//exception occurs statement 6; statement 7; statement 8; statement 9; statement 10;
Suppose there are 10 statements in your program and there occurs an exception at statement 5, the rest of the code will not be executed i.e. statement 6 to 10 will not be executed. If we perform exception handling, the rest of the statement will be executed. That is why we use exception handling in Java.
The java.lang.Throwable class is the root class of Java Exception hierarchy which is inherited by two subclasses: Exception and Error. A hierarchy of Java Exception classes are given below:
There are mainly two types of exceptions: checked and unchecked. Here, an error is considered as the unchecked exception. According to Oracle, there are three types of exceptions:
The classes which directly inherit Throwable class except RuntimeException and Error are known as checked exceptions e.g. IOException, SQLException etc. Checked exceptions are checked at compile-time.
The classes which inherit RuntimeException are known as unchecked exceptions e.g. ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException etc. Unchecked exceptions are not checked at compile-time, but they are checked at runtime.
Error is irrecoverable e.g. OutOfMemoryError, VirtualMachineError, AssertionError etc.
There are 5 keywords which are used in handling exceptions in Java.
| Keyword | Description |
|---|---|
| try | The "try" keyword is used to specify a block where we should place exception code. The try block must be followed by either catch or finally. It means, we can't use try block alone. |
| catch | The "catch" block is used to handle the exception. It must be preceded by try block which means we can't use catch block alone. It can be followed by finally block later. |
| finally | The "finally" block is used to execute the important code of the program. It is executed whether an exception is handled or not. |
| throw | The "throw" keyword is used to throw an exception. |
| throws | The "throws" keyword is used to declare exceptions. It doesn't throw an exception. It specifies that there may occur an exception in the method. It is always used with method signature. |
Let's see an example of Java Exception Handling where we using a try-catch statement to handle the exception.
public class JavaExceptionExample{
public static void main(String args[]){
try{
//code that may raise exception
int data=100/0;
}catch(ArithmeticException e){System.out.println(e);}
//rest code of the program
System.out.println("rest of the code...");
}
}In the above example, 100/0 raises an ArithmeticException which is handled by a try-catch block.
There are given some scenarios where unchecked exceptions may occur. They are as follows:
If we divide any number by zero, there occurs an ArithmeticException.
int a=50/0;//ArithmeticException
If we have a null value in any variable, performing any operation on the variable throws a NullPointerException.
String s=null; System.out.println(s.length());//NullPointerException
The wrong formatting of any value may occur NumberFormatException. Suppose I have a string variable that has characters, converting this variable into digit will occur NumberFormatException.
String s="abc"; int i=Integer.parseInt(s);//NumberFormatException
If you are inserting any value in the wrong index, it would result in ArrayIndexOutOfBoundsException as shown below:
int a[]=new int[5]; a[10]=50; //ArrayIndexOutOfBoundsException
