Checked and Unchecked Exceptions in Java

There are two types of exceptions in Java i.e. checked and unchecked exceptions. Below I have explained about these two exceptions with examples.

Checked and Unchecked Exceptions in Java

Checked Exceptions

Those exceptions that are checked at compilation time are called checked exceptions.
Checked exception includes the classes that extend Throwable class except RuntimeException and Error.

Some examples of checked exceptions are:
- InvocationTargetException
- SQLException
- ClassNotFoundException
- IOException

If a method throws checked exceptions then it must handle them by try catch block or declare the exceptions by throws keyword.

Consider below example.

package com;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class JDBCMySQL {
	public static void main(String args[]) {
		Class.forName("com.mysql.jdbc.Driver");
			
		Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","root");
			
		Statement st = con.createStatement();
		ResultSet rs = st.executeQuery("select * from login");
			
		while(rs.next()){
			System.out.println(rs.getString(1)+" "+rs.getString(2)+" "+rs.getString(3));
		}
			
		con.close();
	}
}

package com;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

public class JDBCMySQL {

public static void main(String args[]) {

Class.forName("com.mysql.jdbc.Driver");

Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","root");

Statement st = con.createStatement();

ResultSet rs = st.executeQuery("select * from login");

while(rs.next()){

System.out.println(rs.getString(1)+" "+rs.getString(2)+" "+rs.getString(3));

}

con.close();

}

When you will run this program you will get following compilation error.

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
	Unhandled exception type ClassNotFoundException
	Unhandled exception type SQLException
	Unhandled exception type SQLException
	Unhandled exception type SQLException
	Unhandled exception type SQLException
	Unhandled exception type SQLException
	Unhandled exception type SQLException
	Unhandled exception type SQLException
	Unhandled exception type SQLException

	at com.JDBCMySQL.main(JDBCMySQL.java:10)

Exception in thread "main" java.lang.Error: Unresolved compilation problems:

Unhandled exception type ClassNotFoundException

Unhandled exception type SQLException

at com.JDBCMySQL.main(JDBCMySQL.java:10)

This error can be solved in two ways.

1. Using try catch block

We can handle the exception using try catch block in following way.

package com;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class JDBCMySQL {
	public static void main(String args[]){
		try{
			Class.forName("com.mysql.jdbc.Driver");
			
			Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","root");
			
			Statement st = con.createStatement();
			ResultSet rs = st.executeQuery("select * from login");
			
			while(rs.next()){
				System.out.println(rs.getString(1)+" "+rs.getString(2)+" "+rs.getString(3));
			}
			
			con.close();
		}
		catch(SQLException e){
			System.out.println("(SQLException Occured");
			e.printStackTrace();
		}
		catch(ClassNotFoundException e){
			System.out.println("(ClassNotFoundException Occured");			
		}
	}
}

package com;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

public class JDBCMySQL {

public static void main(String args[]){

try{

Class.forName("com.mysql.jdbc.Driver");

Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","root");

Statement st = con.createStatement();

ResultSet rs = st.executeQuery("select * from login");

while(rs.next()){

System.out.println(rs.getString(1)+" "+rs.getString(2)+" "+rs.getString(3));

}

con.close();

}

catch(SQLException e){

System.out.println("(SQLException Occured");

e.printStackTrace();

}

catch(ClassNotFoundException e){

System.out.println("(ClassNotFoundException Occured");

}

2. Using throws keyword

We can also handle exception using throws keyword in following way.

package com;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class JDBCMySQL {
	public static void main(String args[]) throws ClassNotFoundException, SQLException{
		Class.forName("com.mysql.jdbc.Driver");
			
		Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","root");
			
		Statement st = con.createStatement();
		ResultSet rs = st.executeQuery("select * from login");
			
		while(rs.next()){
			System.out.println(rs.getString(1)+" "+rs.getString(2)+" "+rs.getString(3));
		}
			
		con.close();
	}
}

package com;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

public class JDBCMySQL {

public static void main(String args[]) throws ClassNotFoundException, SQLException{

Class.forName("com.mysql.jdbc.Driver");

Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","root");

Statement st = con.createStatement();

ResultSet rs = st.executeQuery("select * from login");

while(rs.next()){

System.out.println(rs.getString(1)+" "+rs.getString(2)+" "+rs.getString(3));

}

con.close();

}

Unchecked Exceptions

The exceptions that are not checked at compilation time are called unchecked exceptions.
These exceptions occur at run time due to some bad data. For example if a program tries to divide a number with zero then it will cause ArithmeticException and result in program termination if not handled.

Unchecked exception includes the classes that extend RuntimeExcpetion class.
Some examples of unchecked exceptions are:
- IllegalArgumentException
- NullPointerException
- ArithmeticException
- ArrayIndexOutOfBoundsException

Although these exceptions are not checked at compilation time but we must handle them properly.

Consider below example.

package com;

public class ExceptionDemo {
	public static void main(String args[]){
		int a=5, b=0, c;
		
		c = a/b;	//this will cause ArithmeticException
	}
}

package com;

public class ExceptionDemo {

public static void main(String args[]){

int a=5, b=0, c;

c = a/b; //this will cause ArithmeticException

}

The above program will compile perfectly but will show following error when you will run it.

Exception in thread "main" java.lang.ArithmeticException: / by zero
	at com.ExceptionDemo.main(ExceptionDemo.java:7)

1 2	Exception in thread "main" java.lang.ArithmeticException: / by zero at com.ExceptionDemo.main(ExceptionDemo.java:7)

We can handle it using try catch block.

package com;

public class ExceptionDemo {
	public static void main(String args[]){
		int a=5, b=0, c;
		try{
			c = a/b;	//this will cause ArithmeticException
		}
		catch(ArithmeticException e){
			System.out.println("ArithmeticException Occurred\nYou are trying to divide by zero");
		}
	}
}

package com;

public class ExceptionDemo {

public static void main(String args[]){

int a=5, b=0, c;

try{

c = a/b; //this will cause ArithmeticException

}

catch(ArithmeticException e){

System.out.println("ArithmeticException Occurred\nYou are trying to divide by zero");

}

Comment below if you found anything incorrect or have queries related to above tutorial for checked and unchecked exceptions in java.

Checked and Unchecked Exceptions in Java

Checked and Unchecked Exceptions in Java

Checked Exceptions

1. Using try catch block

2. Using throws keyword

Unchecked Exceptions

1 thought on “Checked and Unchecked Exceptions in Java”

Leave a Comment Cancel Reply

Checked and Unchecked Exceptions in Java

Checked Exceptions

1. Using try catch block

2. Using throws keyword

Unchecked Exceptions

Related Posts

1 thought on “Checked and Unchecked Exceptions in Java”

Leave a Comment Cancel Reply