We give the specifications of some of the method of class JFrame in Fig. 1.6.
We encourage you to experiment with class JFrame in your IDE. Create a
JFrame and assign its name to a variable such as window . Then, practice using
the methods of Fig. 1.6. For example, you can find out the width of window win-
dow by evaluating the call window.getWidth() and set the position of the win-
dow to ( 200 , 300) by having this statement executed:
As a more complex example, we develop statements that will change the
height of window window to its width, thus making the window a square. To do
this, we do two things:
1. Obtain the width of the window and store it in variable jfWidth ;
2. Change the height of the window to jfWidth .
When determining how to perform a programming task, it helps to write it
down in English as a sequence of steps to be performed, as above. Then, we can
figure out how to write each of the steps in Java. Separating what to do from how
to do it is an example of separation of concerns , which is an important strategy
in any problem-solving task. Use it consciously to focus on one thing at a time.
We are also using a methodology called stepwise refinement . The develop-
ment consists of a series of steps. At each step, we “refine” part of the task into
more detailed steps, some of them in English and some of them in Java, until the
whole task has been written in Java. We discuss stepwise refinement in Sec. 2.5.
We return to the task of refining the two steps given above into Java. To see
how to obtain the width of the window (step 1), we look through the list of meth-
ods described in Fig. 1.6. There it is: method getWidth will do the trick. So, we
can write a statement:
window.show(); Show window window .
window.hide(); Hide window window .
window.getHeight() = height of window window , in pixels
window.getWidth() = width of window window , in pixels
window.setSize(w,h); Set width and height of window window to w and h
window.getX() = x - coordinate of top left corner of window window
window.getY() = y - coordinate of top left corner of window window
window.setLocation(x,y); Set x - and y -coordinates of top left corner of window to x , y
= the title of window window (in the title bar)
Set the title of window window to s (a String ).
= “window window can be resized by dragging it”
If b is true ( false ) make window resizable (not resizable).
Calls on some methods in an instance window of a JFrame