Difference between Checked and Unchecked Exceptions in Java

There are two types of exceptions - checked and unchecked. The main difference between checked and unchecked exception is that checked exceptions are checked at compile-time, while unchecked exceptions are checked at runtime.

Exception hierarchy

Here, all the classes under RuntimeException and Error are Unchecked Exceptions, while all the classes direcly under Exception class are Checked Exceptions.

Checked exceptions 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 throws keyword.

FileNotFoundException is a checked exception in Java. Anytime, we want to read a file from filesystem, Java forces us to handle error situation where file may not be present in place.

public class Demo {
	public static void main(String[] args) 
	{
		FileReader file = new FileReader("somefile.txt");
	}
}

In above case, you will get compile time error with message – Unhandled exception type FileNotFoundException.

We can reslove this error in two ways either we can propogate this exception further using throws keyword or we can handle this exception using try-catch blocks.

// Method 1: Declare the exception using throws keyword.
public class Test {
    public static void main(String[] args) throws FileNotFoundException
    {
        FileReader file = new FileReader("somefile.txt");
    }
} 
 
// Method 2: Handle the exception using try-catch blocks.
public class Demo {
	public static void main(String[] args) 
	{
		try
		{
			FileReader file = new FileReader("somefile.txt");
		} 
		catch (FileNotFoundException e) 
		{
			//Alternate logic
			e.printStackTrace();
		}
	}
}

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