Write a Java program to create a GUI window with a label and a button. Consider three variables x, y and z with values as follows: x=12, y=34, z=87. When the user clicks the button, the program should display the output as follows: Average of these numbers is 44.3 The output should be displayed on the GUI window using a label. To display this output, you are required to use appropriate Java logic and other elements such as operators, loops, If-else etc.