MyUtils

 

In this exercise we'll start building our own class of utilities.

Start by creating the project "MyUtils" in NetBeans, uncheck the "Create Main Class", and create a class MyUtils.

max(int, int) and min(int, int)
We will start by putting two utilities - max() and min() in this class.

Implement the two methods using the following guidelines:

• Both methods should be static as hey are not accessing values from any object - thus they should be class-methods.
• Both methods are public, returns an int value and takes two int values as parameters.
• The method max() returns the largest of the two parameters and min()returns the smallest of the two parameters.
• You should implement the code in the two methods using an if-else statement!

Testing the utilities
Now we'll build a program that tests the utilities.

You can copy the the form from "Readinput03" or create e new form from scratch. If you copy from "Readinput03" you must remember to adapt the labels and maybe also names of some of the components.

Your form should look something like this:

The code associated with click on the button should do the following:

• read values from the two text-fields and store the values in two Strings
• transfer the two strings into two int values (using Integer.parseInt())
• clear the two text-fields (using setText("");)
• use the two int values to activate the two methods max() and min() and store the results (in int variables)
• output a message that shows the input for the methods and the results

If you used -2 and 14 as input the window should look something like:

Checking for no input (optional)
Before we move on we'd like to be able to check whether the user actually entered any input in the two text-fields.

Remember that we store the result from the text-fields in Strings using the getText() method?
So what we would like to do is to check whether these strings are empty or not.
To check the value of a String we use the method equals() defined in the String class:

Assume we have the following declaration: String myString;
If the string is empty then myString.equals("") will return true (and otherwise false)

• Adapt the method associated with click on the button so it checks whether the strings from the text-fields are empty.
  

If they are empty it would be a mistake to perform the parseInt() (there is nothing to parse from).

• So if the strings are empty the method should only give an error-message in the output area.
  If they are not empty the method should do what it did before.

Please note that another mistake could be that the strings actually do have a value, but it is not expressing an int value (like "Hi 123"). In that case the parseInt() method will show error-messages in the NetBeans Output area - later we'll learn how to solve this problem more elegantly.

Extending to three input values
Now we'll extend the utility class.

• Implement a max() method that takes three int values as parameters and returns the largest of these.
  Also implement a min() method that takes three parameters.

The form should be changed so it can test these new methods as well:

• Add a label and a text-field so the user can enter three values.

In the method associated with click on the button you should now do the following:

• if one (or both) of the first two text-fields are empty you should simply show an error-message in the output area
• if the third text-field is empty but the first two have values you should simply use the methods from MyUtils that takes two parameters
• if all three text-fields have values you should use the methods from MyUtils that takes three parameters