Checked Exceptions in Java
These are the exceptions that are checked at compile time. If some code within a method throws a checked exception, then the method must either handle the exception or it must specify the exception using the throws keyword. In checked exceptions, there are two types: fully checked and partially checked exceptions. A fully checked exception is a checked exception where all its child classes are also checked, like IOException, and InterruptedException. A partially checked exception is a checked exception where some of its child classes are unchecked, like an Exception.
For example, consider the following Java program that opens the file at location “C:\test\a.txt” and prints the first three lines of it. The program doesn’t compile, because the function main() uses FileReader(), and FileReader() throws a checked exception FileNotFoundException. It also uses readLine() and close() methods, and these methods also throw checked exception IOException
Example:
Java
// Java Program to Illustrate Checked Exceptions// Where FileNotFoundException occurred// Importing I/O classesimport java.io.*;// Main classclass GFG { // Main driver method public static void main(String[] args) { // Reading file from path in local directory FileReader file = new FileReader("C:\\test\\a.txt"); // Creating object as one of ways of taking input BufferedReader fileInput = new BufferedReader(file); // Printing first 3 lines of file "C:\test\a.txt" for (int counter = 0; counter < 3; counter++) System.out.println(fileInput.readLine()); // Closing file connections // using close() method fileInput.close(); }} |
Output:
To fix the above program, we either need to specify a list of exceptions using throws, or we need to use a try-catch block. We have used throws in the below program. Since FileNotFoundException is a subclass of IOException, we can just specify IOException in the throws list and make the above program compiler-error-free.
Example:
Java
// Java Program to Illustrate Checked Exceptions// Where FileNotFoundException does not occur// Importing I/O classesimport java.io.*;// Main classclass GFG { // Main driver method public static void main(String[] args) throws IOException { // Creating a file and reading from local repository FileReader file = new FileReader("C:\\test\\a.txt"); // Reading content inside a file BufferedReader fileInput = new BufferedReader(file); // Printing first 3 lines of file "C:\test\a.txt" for (int counter = 0; counter < 3; counter++) System.out.println(fileInput.readLine()); // Closing all file connections // using close() method // Good practice to avoid any memory leakage fileInput.close(); }} |
Output:
First three lines of file "C:\test\a.txt"
Checked vs Unchecked Exceptions in Java
In Java, Exception is an unwanted or unexpected event, which occurs during the execution of a program, i.e. at run time, that disrupts the normal flow of the program’s instructions.
In Java, there are two types of exceptions:
- Checked exceptions
- Unchecked exceptions