Exercise: Exceptions

Create a Phone class

Task Description:

Let's get some practice handling Exceptions. First, we will create a Phone class:

Task List:

Create a new Java Project and name it lesson4.

Create a new package under the src folder named exceptionExample.

Create a new class named Phone in the ** exceptionExample** package.

Add the following variables: String phoneType;,String phoneNumber;.

Create a constructor that sets the variables.

In the constructor, before the variables are set, add a conditional check to see if the phoneType or phoneNumber are null. If they are, throw an exception: if (phoneType == null || phoneNumber == null) { throw new IllegalArgumentException("The type and number cannot be null"); }

Create getter functions for the variables.

Create the setter functions for the variables.

Override the toString method.

Task Feedback:

Nice work!

Create a PhoneExceptionTester

Task Description:

Next, let's create a PhoneExceptionTester class to test how exception flow works in Java:

Task List:

Create a new class, PhoneExceptionTester.

Create a main method: public static void main(String[] args){}

Inside the main method, create an array of phone numbers, making one of them null: String[] numbers = new String[] { "123-4567", null, "234-4567", "345-5678" };

Next, we need to create a for loop to iterate over the array: for (int i = 0; i < numbers.length; i++) {}

Inside the loop, we want to add our try and catch logic. Inside the try block, we want code that will take each of the numbers and try to create a new Phone object: System.out.println(new Phone("iPhone", numbers[i]));

For the catch block, we need to generate an illegal argument exception: catch (IllegalArgumentException ex) { }. And inside that block, we then want to print out the message for this exception: System.out.println(ex.getLocalizedMessage());.

To try it out, right click on the PhoneExceptionTester and select run.

Task Feedback:

Nice work!

Solution

ND079 C1 L4 A04 Exception Solutions

The important point to note is that without the try and catch block, the program would terminate with an exception.

public class Phone {
    private final String phoneType;
    private final String phoneNumber;

    public Phone(String phoneType, String phoneNumber) {
        super();

        if (phoneType == null || phoneNumber == null) {
            throw new IllegalArgumentException("The type and number cannot be null");
        }
        this.phoneType = phoneType;
        this.phoneNumber = phoneNumber;
    }

    public String getPhoneType() {
        return phoneType;
    }

    public String getPhoneNumber() {
        return phoneNumber;
    }

    @Override
    public String toString() {
        return phoneType + " " + phoneNumber;
    }

}

public class PhoneExceptionTester {

    public static void main(String[] args) {
        String[] numbers = new String[] { "123-4567", null, "234-4567", "345-5678" };

        for (int i = 0; i < numbers.length; i++) {
            try {
                System.out.println(new Phone("iPhone", numbers[i]));
            } catch (IllegalArgumentException ex) {
                System.out.println(ex.getLocalizedMessage());
            }

        }

        for (int i = 0; i < numbers.length; i++) {
            System.out.println(new Phone("iPhone", numbers[i]));

        }
    }

}

Remember:

You can create and throw your own exceptions by extending the Exception classes
There are two types of exceptions in Java: Checked and unchecked. Checked exceptions will get caught at compile time and will not allow the code to build until they are either in a catch block or thrown. Unchecked (or runtime) exceptions are not checked by the compiler.