Java程序辅导

1001ICT Introduction To Programming
Lecture Notes
School of Information and Communication Technology
Griffith University
Semester 2, 2015
1
5 Hello, NXT!
In this section we learn how to compile Making Stuff Happen (MaSH) (and
Java) programs for the NXT, and how to upload them.
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5.1 Procedures come from environments
In our first MaSH program:
import console;
println("Hello, World!");
• We import the console environment, because the program will run
on a PC and we want to print stuff on the console screen.
• We use the println(String) procedure, because that is one of
the procedures in the console environment that will output a string
to a personal computer (PC)’s console.
• Procedures are not built into or predefined in the language.
• In a different environment, there will be different procedures.
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5.2 A Hello program for the NXT
Let’s write a program that puts a hello message on the screen of an NXT.
Some considerations:
• We must import the right environment: nxt.
• A procedure in the nxt environment that puts text on the screen is
drawString(String, int, int).
Where int and int indicate we have to supply numbers, not just the
string.
The numbers are the column and row on the screen at which to start
drawing the string.
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• When the program ends, the screen reverts to the Lejos menus, so we
need to get the program to pause until we have read the text.
We can make the program wait until a touch sensor is pressed, before
it ends.
There’s a procedure for that: waitForPush(int).
The number is the input port number that a touch sensor is plugged
into.
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• If a program uses a sensor, that sensor has to be set up.
There’s a procedure for that: setUpSensor(int, int).
The first number is the input port number.
The second number is a number used to select the kind of sensor that
is plugged into that port.
To avoid having programs littered with numbers with special mean-
ings that you would not remember and would need to look up, the
nxt environment defines some symbolic constants: TOUCH, SOUND,
...
• If we choose input port 4, this program will work on a Tricorder.
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Putting it all together:
import nxt;
setUpSensor(4, TOUCH);
drawString("Hello, NXT!", 0, 4);
waitForPush(4);
This is the program you compile and run in Lab 2.
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5.3 Compiling and running a MaSH NXT program
5.3.1 Step 1: Create the program file
Use your favourite text editor to create a text containing the text of the
program.
The file must have a name that ends with the extension .mash.
The main part of file name must be a Java identifier, starting with an upper
case letter.
5.3.2 Step 2: Compile with mashc
Compile a MaSH program with a command like:
$ mashc Program.mash
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5.3.3 Step 3: Compile with nxjc
Different! Compile the Java program with a command like:
$ nxjc Program.java
nxjc.bat is a batch file that makes javac use the Lejos NXJ libraries.
5.3.4 Step 4: Link with nxjlink
Linking means bundling up all the compiled code into one file.
Do this with a command like:
$ nxjlink Program -o Program.nxj
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5.3.5 Step 5: Upload to the NXT with nxjupload
Do this with a command like:
$ nxjupload Program
5.3.6 Step 4 and 5 shortcut
The nxj command can be used to link and upload in one step.
$ nxj Program
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5.4 Convenience batch files for Windows
This is getting to be a lot of steps!
We have installed batch files in the lab PCs.
5.4.1 For console programs
As mentioned before, command:
> mash Program
will compile a program with mashc then javac and then run it with
java. (Don’t type any filename extension!)
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5.4.2 For NXT programs
The command:
> mashn Program
will compile a program with mashc and nxjc, then link and upload it with
nxj.
5.4.3 For RCX programs
The command:
> mashl Program
performs the equivalent for Robotic Command eXplorer (RCX) programs.
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5.5 Convenience shell script for Macs and Linux
For Unix (that is Mac OS X) and Linux, the previously mentioned bash
shell script works for all MaSH environments.
] mc Program
mc will compile a program with mashc then javac or nxjc and then run
it with java or link and upload it with nxj. (Don’t type any extension
other than .mash.)
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5.6 Section summary
This section covered:
• an example program that uses the nxt environment;
• how to compile, link, and upload an nxt program; and
• the batch files for convenient compiling.
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5.7 End of section feedback questions
Send us your answers to these questions any time you like by clicking on
them.
• What was the most useful topic in this section?
• What was the least useful topic in this section?
• What was the least clear topic in this section?
• What topic in this section would you like to know more about?
• Did you find an error in this section?
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