Top 10 exceptions in java
Based on the person who is raising an exception all exceptions are divided into 2 category.
- JVM Exception
- Programmatic Exception
JVM Exception:
The exception which are raised automatically by JVM whenever a particular event occurs are called JVM exception.
Ex: ArithmeticException, NullPointerException, ......
Programmatic Exception:
The exception which are raised explicitly either by programmer or by API developer to indicate that something goes wrong are called programmatic exception.
Ex: TooOldException, TooYoungException, .....
1. ArrayIndexOutOfBoundException:-
- It is the child class of RuntimeException and it is unchecked.
- Raised automatically by JVM whenever we are trying to access array element with out of range index.
Ex:-
int[] x = new int[4]; // 0 to 3
System.out.println( x[0] );
System.out.println( x[10] ); // RE: ArrayIndexOutOfBoundException
System.out.println( x[10] ); // RE: ArrayIndexOutOfBoundException
System.out.println( x[22] ); // RE: ArrayIndexOutOfBoundException
2. NullPointerException:-
- It is the child class of RuntimeException and it is unchecked.
- Raised automatically by JVM whenever we are trying to perform any operation on null.
String s = null;
System.out.println( s.length() ); // RE: NullPointerException
3. ClassCastException:-
- It is the child class of RuntimeException and it is unchecked.
- Raised automatically by JVM whenever we are trying to type cast parent object to child object.
Ex:
Object o = new Object();
String s = (String) o ; // RE: ClassCastException
String s = new String("Raka");
Object o = (Object) s; // No error
Object o = new String();
String s = (String) o ; // No error
4. StackOverFlowError:-
- It is the child class of Error and it is unchecked.
- Raised automatically by JVM whenever we are trying to perform recursive method call.
5. NoClassDefFoundError:-
- It is the child class of Error and it is unchecked.
- Raised automatically by JVM whenever JVM unable to find required .class file.
Ex: java Test ( if Test.class file is not available then we will get RE: NoClassDefFoundError: Test)
6. ExceptionInInitializerError:-
- It is the child class of Error and it is unchecked.
- Raised automatically by JVM if any exception occurs while executing static variable assignment and static blocks
Ex:
class Test
{
static int a = 10/0;
}
RE: Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.ArithmeticException: / by zero
at com.test.Test.<clinit>(Test.java:5)
Caused by: java.lang.ArithmeticException: / by zero
at com.test.Test.<clinit>(Test.java:5)
class Test
{
static {
String s = null;
SOP( s.toString() );
}
}
RE: Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.NullPointerException
at com.test.Test.<clinit>(Test.java:7)
Caused by: java.lang.NullPointerException
at com.test.Test.<clinit>(Test.java:7)
7. IlligalArgumentException:-
- It is the child class of RunTimeException and it is unchecked.
- Raised explicitly either by programmer or by API developer to indicate that a method has been invoked with illegal argument.
Ex: The valid range of Thread priorities is 1 - 10. If we are trying to set the priority with any other value then we will get RuntimeException saying IllegalArgumentException.
Thread t = new Thread();
t.setPriority(7);
t.setPriority(15); // RE: IllegalArgumentException
8. NumberFormatException:-
- It is the direct child class of IllegalArgumentException which is child of RunTimeException and hence it is unchecked.
- Raised explicitly either by programmer or by API developer to indicate that we are trying to convert string to number and the string is not properly formated.
Ex:
int i= Integer.parseInt("100"); // No error
int i= Integer.parseInt("Raka"); // RE: NumberFormatException
9. IllegalStateException:-
- It is the child class of RunTimeException and it is unchecked.
- Raised explicitly either by programmer or by API developer to indicate that a method has been invoked at wrong time.
Ex: After starting thread, we are not allowed to restart once again, otherwise we will get run time exception saying IllegalStateException.
Thread t = new Thread();
t.start();
t.start(); // IllegalStateException
10. AssertionError:-
- It is the child class of Error and it is unchecked.
- Raised explicitly either by programmer or by API developer to indicate that assert statement that fails.
Ex: assert ( x>10 )
If x is not greater than 10 then we will get RuntimeException: AssertionError
