CS1110 Lab 02. Creating objects, calling their methods, and writing
subclasses Fall 2008
Name _________________ Netid _____ Section time __________ Section instructor
___________________
We ask you to experiment with creating objects, calling their methods, and writing subclasses. At the end of
this handout is a list of oft-used methods of class JFrame.
Task 1. Practicing calling methods of objects
(a) In DrJava, using the interactions pane, create two different objects of class javax.swing.JFrame and show
them. You can drag them to different places. See Sec. 1.3.2 of the text. You create a JFrame folder and
store its name in a variable jf1 using the assignment "jf1= new javax.swing.JFrame();". Or, use the import
statement —execute
import javax.swing.*;
jf1= new JFrame();
(b) Try out these method calls. In the table below, we show calls on the methods, using three dots ... to
denote the position of an argument, which you have to fill in when you type in the call in the DrJava
interactions pane. For a function call, write the value that the function call returns, so that we know that you
tried such a call. For a procedure call, just put a check next to it. You can call these methods as many times
as you want. Experiment.
show(); getWidth()
setSize(..., ...); getHeight()
setLocation(..., ...); getX()
setTitle(...); getY()
Describe BRIEFLY, below, the syntactic and semantic differences between the methods (and calls on them)
being called in the left column and those being called in the right. Hint: what kind of method is called in the
left column and what kind on the right? Syntax refers to grammar, structure. Semantics refers to meaning —
in programming, how a statement is executed or an expression is evaluated.
Task 2. Positioning JFrames
Reset the Interactions pane (by clicking button "reset"). Create two new JFrames (assigning their names to
variables).
Make the first window 120 x220 pixels and the second window 220 x 120 pixels (by calling appropriate
methods). Which coordinate comes first, the horizontal or vertical coordinate? (Write your answer below).
Check your answer by calling methods getWidth and getHeight of one of the JFrames.
