Handling errors during the execution of programs

During the execution of a program, various conditions can occur that cause an unexpected and abnormal termination of the program.

Example: Consider the following program:

public class TestException {
  public static void main (String[] args) {
    int falseNumber = Integer.parseInt("OK");
    System.out.println("this println statement is not executed");
  }
}

the following message is printed on the screen:

Exception in thread "main" java.lang.NumberFormatException: For input string: "OK"
  at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
  at java.lang.Integer.parseInt(Integer.java:468)
  at java.lang.Integer.parseInt(Integer.java:518)
  at TestException.main(TestException.java:3)

Hence, the string "this println statement is not executed" is not printed.

In Java, the errors that occur at runtime are represented by means of exceptions. Java offers a predefined set of exceptions that can be thrown during program execution.

To avoid that a program terminates unexpectedly, Java allows us to handle exceptions by means of a suitable construct.