Checked exceptions are the subclass of the Exception class. These types of exceptions need to be handled during the compile time of the program. These exceptions can be handled by the try-catch block or by using throws keyword otherwise the program will give a compilation error.
ClassNotFoundException, IOException, SQLException etc are the examples of the checked exceptions.
I/O Exception: This Program throws an I/O exception because of due FileNotFoundException is a checked exception in Java. Anytime, we want to read a file from the file system, Java forces us to handle error situations where the file is not present in the given location.
Implementation: Consider GFG.txt file does not exist.
Example 1-A:
Java
// Java Program to Handle Checked Exception// Where FileInputStream Exception is thrown// Importing required classesimport java.io.*;// Main classclass GFG { // Main driver method public static void main(String args[]) { // Reading content from file by passing local directory path // where file should exists FileInputStream GFG = new FileInputStream("/Desktop/GFG.txt"); // This file does not exist in the location // This constructor FileInputStream // throws FileNotFoundException which // is a checked exception }} |
Output:
Now let us do discuss how to handle FileNotFoundException. The answer is quite simple as we can handle it with the help of a try-catch block
- Declare the function using the throw keyword to avoid a Compilation error.
- All the exceptions throw objects when they occur try statement allows you to define a block of code to be tested for errors and catch block captures the given exception object and perform required operations.
- Using a try-catch block defined output will be shown.
Example 1-B:
Java
// Java Program to Illustrate Handling of Checked Exception// Importing required classesimport java.io.*;import java.util.*;// Main classclass GFG { // Main driver method public static void main(String[] args) throws FileNotFoundException { // Assigning null value to object of FileInputStream FileInputStream GFG = null; // Try block to check for exceptions try { // Giving path where file should exists to read // content GFG = new FileInputStream( "/home/mayur/GFG.txt"); } // Catch block to handle exceptions catch (FileNotFoundException e) { // Display message when exception occurs System.out.println("File does not exist"); } }} |
File does not exist
Now let us discuss one more checked exception which is ClassNotFoundException. This Exception occurs when methods like Class.forName() and LoadClass Method etc. are unable to find the given class name as a parameter.
Example 2-A
Java
// Java Program to Handle Checked Exception// Importing required classesimport java.io.*;// Main classclass GFG { // Main driver method public static void main(String[] args) { // Calling the class gfg which is not present in the // current class temp instance of calling class Class temp = Class.forName("gfg"); // It will throw ClassNotFoundException }} |
Output:
Again now let us handle ClassNotFoundException using the try-Catch block.
Example 2-B
Java
// Java Program to Handle Checked Exceptionimport java.io.*;// Classclass GFG { // Main driver method public static void main(String[] args) throws ClassNotFoundException { // Try block to check for exceptions try { Class temp = Class.forName( "gfg"); // calling the gfg class } // Catch block to handle the exceptions catch (ClassNotFoundException e) { // block executes when mention exception occur System.out.println( "Class does not exist check the name of the class"); } }} |
Class does not exist check the name of the class
SQLException – The SQLException is a checked exception that we need to handle explicitly.
- The SQL exception mainly occurs during the connection of the database from Java program.
In this example, we are trying to connect the PostgreSQL database from the Java program, here everything is syntactically correct but we haven’t said to the compiler that the main method will be going to throw a SQLException. Because of this, it will give us a compile time error as shown in the below output image.
Example 3-A
Java
// Importing required classesimport java.io.*;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;// Classpublic class sql_excep { // Main driver method public static void main(String[] args) { Connection con = getConnection("javaDb", "postgres", "abrar"); } public static Connection getConnection(String dbname, String user, String pass) throws SQLException { Connection con_obj = null; con_obj = DriverManager.getConnection(url + dbname, user, pass); if (con_obj != null) { System.out.println( "Connection established successfully !"); } else { System.out.println("Connection failed !!"); } return con_obj; }} |
Output:
We can handle this in two ways.
- Using throws keyword at main method signature.
- Using try/catch block.
Example 3-B: throws
Java
// Importing required classesimport java.io.*;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;// Classpublic class sql_excep { // Main driver method public static void main(String[] args) throws SQLException { Connection con=getConnection("javaDb","postgres","abrar"); } public static Connection getConnection(String dbname,String user,String pass) throws SQLException { Connection con_obj=null; con_obj= DriverManager.getConnection(url+dbname,user,pass); if(con_obj!=null) { System.out.println("Connection established successfully !"); } else { System.out.println("Connection failed !!"); } return con_obj; }} |
Output:
Example 3-C: try/catch
Java
import java.io.*;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;// Classpublic class sql_excep { public static void main(String[] args) { Connection con=getConnection("javaDb","postgres","abrar"); } public static Connection getConnection(String dbname,String user,String pass) { Connection con_obj = null; // Try block t ocheck for exceptions try { con_obj= DriverManager.getConnection(url+dbname,user,pass); if(con_obj!=null) { System.out.println("Connection established successfully !"); } else { System.out.println("Connection failed !!"); } } // Catch block to hanadle exceptions catch (Exception e) { System.out.println(e.getMessage()); } return con_obj; }} |
Output:
