Exception Handling in Java PDF

EXCEPTION HANDLING Presented By : Prof.Honey Parmar  EXCEPTION HANDLING IN JAVA The Exception Handling in Java is one of the powerful mechanism to handle the runtime errors so that the normal flow of the application can be maintained. What is Exception in Java? an exception is an...

EXCEPTION HANDLING Presented By : Prof.Honey Parmar  EXCEPTION HANDLING IN JAVA The Exception Handling in Java is one of the powerful mechanism to handle the runtime errors so that the normal flow of the application can be maintained. What is Exception in Java? an exception is an event that disrupts the normal flow of the program. It is an object which is thrown at runtime. What is Exception Handling? Exception Handling is a mechanism to handle runtime errors such as ClassNotFoundException, IOException, SQLException, RemoteException, etc.  EXCEPTION HANDLING IN JAVA Advantage of Exception Handling 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 need to handle exceptions. Let's consider a scenario:  EXCEPTION HANDLING IN JAVA statement 1; statement 2; statement 3; statement 4; statement 5;//exception occurs statement 6; statement 7; statement 8; statement 9; statement 10;  EXCEPTION HANDLING IN JAVA Suppose there are 10 statements in a Java program and an exception occurs at statement 5; the rest of the code will not be executed, i.e., statements 6 to 10 will not be executed. However, when we perform exception handling, the rest of the statements will be executed. That is why we use exception handling in Java.  EXCEPTION HANDLING IN JAVA Hierarchy of Java Exception classes The java.lang.Throwable class is the root class of Java Exception hierarchy inherited by two subclasses: Exception and Error. The hierarchy of Java Exception classes is given below: EXCEPTION HANDLING IN JAVA  EXCEPTION HANDLING IN JAVA Types of Java Exceptions There are mainly two types of exceptions: checked and unchecked. An error is considered as the unchecked exception. Checked Exception Unchecked Exception  EXCEPTION HANDLING IN JAVA 1) Checked Exception The classes that directly inherit the Throwable class except RuntimeException and Error are known as checked exceptions. For example, IOException, SQLException, etc. Checked exceptions are checked at compile-time. 2) Unchecked Exception The classes that inherit the RuntimeException are known as unchecked exceptions. For example, ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException, etc. Unchecked exceptions are not checked at compile-time, but they are checked at runtime.  EXCEPTION HANDLING IN JAVA Java Exception Keywords 1. try The "try" keyword is used to specify a block where we should place an exception code. It means we can't use try block alone. The try block must be followed by either catch or finally. 2. 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.  EXCEPTION HANDLING IN JAVA 3. finally The "finally" block is used to execute the necessary code of the program. It is executed whether an exception is handled or not. 4. throw The "throw" keyword is used to throw an exception. 5. throws The "throws" keyword is used to declare exceptions. It specifies that there may occur an exception in the method. It doesn't throw an exception. It is always used with method signature.  EXCEPTION HANDLING IN JAVA Common Scenarios of Java Exceptions There are given some scenarios where unchecked exceptions may occur. They are as follows: 1) A scenario where ArithmeticException occurs If we divide any number by zero, there occurs an ArithmeticException. int a=50/0;//ArithmeticException  EXCEPTION HANDLING IN JAVA 2) A scenario where ArrayIndexOutOfBoundsException occurs When an array exceeds to it's size, the ArrayIndexOutOfBoundsException occurs. there may be other reasons to occur ArrayIndexOutOfBoundsException. Consider the following statements. int a[]=new int; a=50; //ArrayIndexOutOfBoundsException  EXCEPTION HANDLING IN JAVA Java try-catch block Java try block Java try block is used to enclose the code that might throw an exception. It must be used within the method. If an exception occurs at the particular statement in the try block, the rest of the block code will not execute. So, it is recommended not to keep the code in try block that will not throw an exception. Java try block must be followed by either catch or finally block.  EXCEPTION HANDLING IN JAVA Syntax of Java try-catch try{ //code that may throw an exception }catch(Exception_class_Name ref){}  EXCEPTION HANDLING IN JAVA Java catch block Java catch block is used to handle the Exception by declaring the type of exception within the parameter. The catch block must be used after the try block only. You can use multiple catch block with a single try block.  EXCEPTION HANDLING IN JAVA Internal Working of Java try-catch block  EXCEPTION HANDLING IN JAVA Problem without exception handling  EXCEPTION HANDLING IN JAVA Solution by exception handling  EXCEPTION HANDLING IN JAVA print a custom message on exception  EXCEPTION HANDLING IN JAVA resolve the exception in a catch block  EXCEPTION HANDLING IN JAVA handle another unchecked exception  EXCEPTION HANDLING IN JAVA Java Catch Multiple Exceptions Java Multi-catch block A try block can be followed by one or more catch blocks. Each catch block must contain a different exception handler. So, if you have to perform different tasks at the occurrence of different exceptions, use java multi-catch block.  EXCEPTION HANDLING IN JAVA Flowchart of Multi-catch Block  EXCEPTION HANDLING IN JAVA Java finally block Java finally block is a block used to execute important code such as closing the connection, etc. Java finally block is always executed whether an exception is handled or not. Therefore, it contains all the necessary statements that need to be printed regardless of the exception occurs or not. EXCEPTION HANDLING IN JAVA CASE 1: WHEN AN EXCEPTION DOES NOT OCCUR CASE 2: WHEN AN EXCEPTION OCCURR BUT NOT HANDLED BY THE CATCH BLOCK  EXCEPTION HANDLING IN JAVA throw Exception throw keyword is used to throw an exception explicitly. We specify the exception object which is to be thrown. The Exception has some message with it that provides the error description. We can throw either checked or unchecked exceptions in Java by throw keyword.  EXCEPTION HANDLING IN JAVA We can also define our own set of conditions and throw an exception explicitly using throw keyword. For example, we can throw ArithmeticException if we divide a number by another number. Here, we just need to set the condition and throw exception using throw keyword. The syntax of the Java throw keyword is given below. throw new exception_class("error message"); Example throw new IOException("device error");  EXCEPTION HANDLING IN JAVA Throwing Unchecked Exception we have created a method named validate() that accepts an integer as a parameter. If the age is less than 18, we are throwing the ArithmeticException otherwise print a message welcome to vote. EXCEPTION HANDLING IN JAVA  EXCEPTION HANDLING IN JAVA Throwing checked Exception If we throw a checked exception using throw keyword, it is must to handle the exception using catch block or the method must declare it using throws declaration. EXCEPTION HANDLING IN JAVA  EXCEPTION HANDLING IN JAVA throws keyword Java throws keyword is used to declare an exception. It gives an information to the programmer that there may occur an exception. So, it is better for the programmer to provide the exception handling code so that the normal flow of the program can be maintained. Syntax of Java throws return_type method_name() throws exception_class_name{ //method code } EXCEPTION HANDLING IN JAVA