Java_Exception-CheatSheet_Edureka.pdf

JAVA EXCEPTIONS CHEAT SHEET Learn JAVA from experts at http://www.edureka.co
Fundamentals of Java Exceptions
Types of Exception in Java with Examples
Exception Hirerachy
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
ClassNotFound, IO, SQL, Remote etc.
Exception Handling Methods
Exception Handling with Method Overriding in Java
Throwable
Error
Virtual Machine Error
Assertion Error etc
Exceptions
Checked Exceptions
Example: IO or Compile
time Exception
Unchecked Exceptions
Example: Runtime or Null
Pointer Exception
Object
Java Exceptions
User -Defined Exceptions
Built-in Exceptions
1. Impossible to recover from error.
2.Errors are of type unchecked
exception.
3. All errors are of type java.lang.error.
4.They are not known to compiler.
They happen at run time.
5.Errors are caused by the enviroment
in which the application is running.
1. Possible to recover from Exception.
2.Exceptions can be checked type or
unchecked type.
3.All exceptions are of type java.lang.
Exception
4.Checked exceptions are known to
compiler where as unchecked
exceptions are not known to compiler.
5.Exceptions are caused by the
application.
class MyException extends
Exception{ String str1;
MyException(String str2) {
str1=str2;
}
public String toString(){
return ("MyException Occurred:
"+str1);
}
}
class Example1{
public static void main(String
args[]){
try{
System.out.println("Start of try
block");
throw new MyException(“Error
Message");
}
catch(MyException exp){
System.out.println("Catch
Block");
System.out.println(exp);
}
}
1.Arithmetic Exception
2.ArrayIndexOutOfBoundException
3.ClassNotFoundException
4.FileNotFoundException
5.IOException
6.InterruptedException
7.NoSuchFieldException
8.NoSuchMethodException
9.NullPointerException
10.NumberFormatException
11.RuntimeException
12.StringIndexOutOfBoundsException
Java throw example
void a(){
throw new ArithmeticException("Incorrect");}
Java throws example
void a()throws ArithmeticException {}
Java throw and throws example
void a()throws ArithmeticException{
throw new ArithmeticException("Incorrect");
}
If the superclass method does not declare an exception
class Parent{
void msg(){System.out.println("parent");}
}
class ExceptionChild extends Parent{
void msg()throws IOException{
System.out.println("ExceptionChild");
}
public static void main(String args[]){ Parent
p=new ExceptionChild();
p.msg();
}
}
Subclass overridden method declares parent
exception
class Parent{
void msg()throwsArithmeticException
{System.out.println("parent");}
}
class ExceptionChild2 extends Parent{
void msg()throws Exception{
System.out.println("child");}
public static void main(String args[]){
Parent p=new ExceptionChild2();
try{
p.msg();
}catch(Exception e){}
}
Exception Handling
User Defined Exceptions
Built-in Exceptions
Java Exceptions
public class ExceptionExample{
public static void main(Stringargs[]){
try{
//code that raise exception
int data=100/0;
}catch(ArithmeticException e){System.out.println(e);}
//rest of the program
System.out.println("rest of the code...");
}
}
Basic Exception
public String getMessage()
public Throwable getCause()
public String toString()
public void printStackTrace()
public StackTraceElement []
getStackTrace()
public Throwable fillInStackTrace()
Exception Methods Common Scenarios
1. ArithmeticException
int a=50/0;
2. NullPointerException
String a=null;
System.out.printn(a.length());
3. NumberFormatException
String s="abc";
int i=Integer.parseInt(s);
4. ArrayIndexOutOfBoundsException
int a[]=new int[5]; a[10]=50;
try - The "try" keyword is used to specify a block where we should place exception code.
catch - The "catch" block is used to handle the exception.
finally - The "finally" block is used to execute the important code of the program.
throw - The "throw" keyword is used to throw an exception.
throws - The "throws" keyword is used to declare exceptions.
try{
//code that throws exception
}catch(Exception_class_Name){}
catch block
public class Sampletrycatch1{
public static void main(String args[])
{
int data=50/0;//throws exception
System.out.println("remaning code");
}
public class SampleMultipleCatchBlock{
try{
int a[]=new int[5]; a[5]=30/0;
}
catch(ArithmeticException e)
{System.out.println("task1 is completed");}
catch(ArrayIndexOutOfBoundsException e)
{System.out.println("task 2 completed");}
catch(Exception e)
{System.out.println("task 3 completed");}
System.out.println("remaining code");
}
}
Nested try block
class Exception{
try{
try{
System.out.println("going to divide");
int b=59/0;
}catch(ArithmeticException e){System.out.println(e);}
try{
int a[]=new int[5]; a[5]=4;
}
catch(ArrayIndexOutOfBoundsException e)
{System.out.println(e);}
System.out.println("other statement);
}catch(Exception e)
{System.out.println("Exception handeled");}
System.out.println("casual flow");
}
}
class SampleFinallyBlock{
try{
int data=55/5;
System.out.println(data);
}
catch(NullPointerException e){System.out.println(e);}
finally{System.out.println("finally block is executed");}
System.out.println("remaining code");
}
}
finally finalize
final
try block
Exception Methods
finally block
Multi catch block
Error vs Exception
throw vs throws
final finally finalise
final is a keyword
Used to apply restrictions on
class, methods and variables
• Final class cannot be
inherited
• Final method cant be
overridden’
• Final variable cant be
changed
finally is a block
Used to place
important code
It will be executed
whether the exception
is handled or not
finalise is a method
Used to perform
clean up
processing just
before the object
is garbage
collected

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