When the flow of instructions is disrupted during the execution of the code, exceptions occur and they should be dealt with to avoid any serious circumstances. 
Java provides a rich set of classes for working with exceptions in java.lang package. These classes include 
● Exception: This is the base class for all exceptions in Java. 
● RuntimeException: This is the base class for all exceptions that occur during the execution of a program. 
● IOException: This is the base class for all exceptions related to I/O operations.

The following code reads a file and catches an IOException if the file is not found:

try { 
FileReader reader = new FileReader("example.txt"); 
// code that reads the file 
reader.close(); 
} catch (IOException e) { 
System.out.println("File not found."); 
} 

You can also throw exceptions explicitly using the "throw" keyword. 
For example, the following code throws an IllegalArgumentException if a negative value is passed to a method: 

public void setValue(int x) { 
if (x < 0) { 
throw new IllegalArgumentException("Value cannot be negative."); 
} 
// code that sets the value 
} 

To handle multiple exceptions, ‘|’ is used: 

try { 
// code that reads a file 
} catch (IOException | FileNotFoundException e) { 
System. out.println("Error reading file."); 
} 

Java also provides a way to define your own exception classes by extending the Exception class. 
Example: 

public class MyException extends Exception { 
public MyException(String message) { 
super(message); 
} 
}