Description
• StopWatch: One of the hallmarks of object-oriented programming is the idea of
easily modeling real-world objects by creating abstract programming objects. As a
simple example, consider StopWatch, which implements the following functions.
After you create one object, you can use method start() to start the watch, then you
can use method stop() to stop the watch. You can use method getElapsedTimeSecs()
to calculate how many seconds elapsed. You also can use method getElapsedTime()
to calculate how many milliseconds elapsed.
The code is listed in the following:
public class StopWatch {
private long startTime = 0;
private long stopTime = 0;
private boolean running = false;
public void start() {
this.startTime = System.currentTimeMillis();
this.running = true;
}
public void stop() {
this.stopTime = System.currentTimeMillis();
this.running = false;
}
//elaspsed time in milliseconds
public long getElapsedTime() {
long elapsed;
if (running) {
elapsed = (System.currentTimeMillis() – startTime);
}
else {
elapsed = (stopTime – startTime);
}
return elapsed;
}
2
//elaspsed time in seconds
public long getElapsedTimeSecs() {
long elapsed;
if (running) {
elapsed = ((System.currentTimeMillis() – startTime) / 1000);
}
else {
elapsed = ((stopTime – startTime) / 1000);
}
return elapsed;
}
//sample usage
public static void main(String[] args) {
StopWatch s = new StopWatch();
s.start();
double z =0.0;
//use scanner to get an string from keyboard
s.stop();
System.out.println(“elapsed time in milliseconds:” +
s.getElapsedTime());
}
}
Add two functions to this sample code:
1. First, please add several statements inside main() method to read one string
from keyboard. Then type string “abc”. This program will return how many
milliseconds you spend on typing.
$ java StopWatch
abc
elapsed time in milliseconds: 2399
2. Second, add method toString() to the StopWatch class. This method result a
string, which contains the elapsed time in millisecond. In addition to that,
replace the following statement in main method
System.out.println(“elapsed time in milliseconds: ” +
s.getElapsedTime());
With
System.out.println(“elapsed time in milliseconds: ” + s);
Whenever we refer to an object, JAVA will execute the toString method
automatically. In this case, object s will be replaced by the method toString(). If
we run this program, we will have
$ java StopWatch
abc
3
elapsed time in milliseconds: 1018
Compiling and running Java programs (reminder):
1. Compile your program using the command javac filename
For example: java myProgram.java
If you receive errors during the compilation phase, re-edit the source code file
and attempt to correct them.
2. Once a file successfully compiles, execute it using the java program.
For example: java MyProgram
What to turn in:
JAR your *.java files into a file called Lab8.jar. When you’re done, submit the
file to Canvas by the deadline. No extensions.
