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Creating User Deifned Packages:
package mypack; public class Pack { public void show() { System.out.println("Inside mypack"); } } Directory name of the package should be as same as the package name From the source file directory compile in the following way:
javac -d. Pack.java Accessing Package import mypack.Pack; class PackageExample { public static void main(String arr[]) { Pack pack=new Pack(); pack.show(); } } www.ardentcollaborations.com [email protected]
Example of using system package: import java.util.Date; class { public static void main(String arr[]) { Date dt=new Date(); System.out.println (―Now=‖+dt); } } www.ardentcollaborations.com [email protected]
ASSIGNMENT: Create a packge. Define a method for addition in it. Now import the package in a class and add two numbers. Take the inputs from user using Scanner class of java.util package. www.ardentcollaborations.com [email protected]
By-Adrish Bhattacharyay
Phone:+91-
http://www.ardentcollaborations.com
CORE JAVA-EXCEPTION HANDLING
Exception Handling Fundamentals
Java has its built-in capability to ensure that
exceptions are handled within the java program.
Exceptions handled by:
Programmer
JVM(Java Runtime System)
Exception Handling Fundamentals
Basically Exceptions occurs due to some run-time
errors.
ex:
When to try to divide some number by zero.
When we try to connect to a database but the DSN is
not created in the system. i.e in case of external
resources.
Exception Handling Fundamentals
When Exception occurs Object Creation(thrown)
A method may choose to handle exception itself and
pass it on.
At the point exception is caught it can be processed or
can be passed again.
Exceptions can be generated by Java Runtime
System or can be manually generated by your
code.
Java Key Words for - Exception Handling try contains block of code that may throw exception. catch Catch the exception thrown. finally contains the block of code that must be executed in the program. throwit manually throws the Exception. throws when a method throws some exception we specify with throws key word. Ex: m1(int a,int b)throws IOException { throw new IOException(); }
try catch finally
try { int d=0; int a=42/d; S.O.P(a); } catch(ArithmeticException e) { e.printStackTrace(); } finally { int z=d*42; S.O.P(z); }
Multiple catch clauses
PSVM(String arr[]) { Scanner sc=new Scanner(System.in); int x=sc.nextLine(); int y=sc.nextLine(); int a[]={x,y}; int b=5; try { int x=a[2]/b-a[1]; } catch(ArithmeticException e) { System.out.println(e); } catch(ArrayIndexOutOfBoundException e) { e.printStackTrace(); } finally { int y=a[1]/a[ ]; System.out.println(“y=”+y); }
throw
Till now whatever be the Exceptions we handled are thrown by Java Runtime
System.
Now we will manually throw the Exception explicitly.
General Form
throw ThrowableInstance;Object of type Throwable or a subclass of
Throwable.
Two ways to obtain Throwable object Using parameters in catch block.
Creating one with new Operator.
throw
Ex:
class ThrowDemo
public void demoproc()
try
throw new NullPointerException(―demo‖);
catch(NullPointerException e)
{S.O.P(―caught‖);
e.printStackTrace();
throw e;
throws
If a method is capable of causing an exception that it does not handle , it must
specify this behaviour so that callers of the method can ground themselves
against that exception.
You do this by including a throws clause in the method declaration. A throw
clause in the method declaration. A throws clause list s the types of exceptions
that a method might throw.
Necessary for all exceptions except error and RuntimeExceptions.
FORMAT:
type mthod-name(parameter list) throws exception-list { //body of method…. }
throws
Example:
class ThrowsDemo { static void throwOne() throws IllegalAccessException { S.O.P(―inside throwOne‖); throw new IllegalAccessException(―demo‖)‘ } public static void main(String arr[]) { try { throwOne(); } catch(IllegalAccessExample e) { e.printStackTrace(); } } docsity.com
