MyUtils

In the class Math you'll find a lot of mathematical functions and utilities that proves extrememly helpful.

In this exercise we'll start building our own class of utilities. We'll start by copying and extending a few of the methods from the Math class, but in the future as you create various methods that might be useful in general you should put a copy of the method in your own toolbox.

Start by creating the project "My utils" in NetBeans, mount a new folder and create a class MyUtils (right-click the folder, choose New -> Java class) .

max(int, int) and min(int, int)
We will start by putting two utilities (max() and min()) in this class that already exists in the Math class - but soon we'll extend their usability.

Implement the two methods using the following guidelines:

• Both methods should be static as they only needs to access values from the parameters (they are not accessing values from any object).
• 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 NOT by using the Math class!!!

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

Create a form (right-click the folder, choose New -> JFrame form), place a JPanel component (give it AbsoluteLayout) at the top.
In the panel place two labels and two text-fields.
Under the panel place a JButton and a JTextArea.

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
• 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 strObj;
If the string is empty then strObj.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 only show an error-message in the output area
• if the third text-field is empty but the first two have values you should use parseInt() to get the two int values and use the methods from MyUtils that takes two parameters
• if all three text-fields have values you should use parseInt() to get the three int values and use the methods from MyUtils that takes three parameters