A really cool piece of code I read today in the book Ruby on Rails: Up and Running.
class Talker
def method_missing(method)
if method.to_s =~ /say_/
puts $'
end
end
end
t = Talker.new
t.say_hello
t.say_something
t.say_goodbye
And running
$ ruby Talker.rb
hello
something
goodbye
But why do that when we have parameters? Because you can do some methods really dynamic with a clear semantic, just looking for them you know are they are doing.
public class PreventTimeTravelers {
public static void main(String args[]){
long startTime = System.currentTimeMillis();
long endTime = System.currentTimeMillis();
assert endTime >= startTime: "We came back in time!";
}
}
Please do not execute this code in a time machine.
NumberFormatException: Thrown to indicate that the application has attempted to convert a string to one of the numeric types, but that the string does not have the appropriate format.
An simple example:
public class SummationExample {
public static void main(String args[]){
int sum = 0;
for(String arg: args){
System.out.println("+" + arg);
sum += Integer.parseInt(arg);
}
System.out.println("= " + sum);
}
}
$ javac SummationExample.java
$ java SummationExample 1 2 3 4 5
+1
+2
+3
+4
+5
= 15
but
$ java SummationExample 1 2 3 4 five
+1
+2
+3
+4
+five
Exception in thread “main” java.lang.NumberFormatException: For input string: “five”
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
at java.lang.Integer.parseInt(Integer.java:447)
at java.lang.Integer.parseInt(Integer.java:497)
at SummationExample.main(SummationExample.java:6)
So
public class SummationExample {
public static void main(String args[]){
int sum = 0;
for(String arg: args){
try {
sum += Integer.parseInt(arg);
System.out.println("+" + arg);
} catch (NumberFormatException e) {
// nothing
}
}
System.out.println("= " + sum);
}
}
now
$ javac BetterSummationExample.java
$ java BetterSummationExample 1 2 3 4 5
+1
+2
+3
+4
+5
= 15
and also
$ java BetterSummationExample 1 2 3 4 five
+1
+2
+3
+4
= 10
I need to implements some codes in C++. Just remembering some concepts like pointers to functions.
A simple example:
#include <stdlib.h>
#include <iostream>
using namespace std;
double evalFunction(double (*f)(double), double param){
return f(param);
}
double function(double x){
return x/2;
}
int main(int argc, char** argv) {
cout << function(5.0) << endl;
cout << evalFunction(function, 5.0) << endl;
return (EXIT_SUCCESS);
}
This code prints out your system properties.
import java.util.Properties;
public class PropertiesLister{
public static void main (String args[]){
Properties props = System.getProperties();
props.list(System.out);
}
}
In the machine I’m writing right now:
— listing properties —
java.runtime.name=Java(TM) SE Runtime Environment
sun.boot.library.path=/usr/lib/jvm/java-6-sun-1.6.0.00/jre/…
java.vm.version=1.6.0-b105
java.vm.vendor=Sun Microsystems Inc.
java.vendor.url=http://java.sun.com/
path.separator=:
java.vm.name=Java HotSpot(TM) Server VM
file.encoding.pkg=sun.io
user.country=BR
sun.java.launcher=SUN_STANDARD
sun.os.patch.level=unknown
java.vm.specification.name=Java Virtual Machine Specification
user.dir=/tmp
java.runtime.version=1.6.0-b105
java.awt.graphicsenv=sun.awt.X11GraphicsEnvironment
java.endorsed.dirs=/usr/lib/jvm/java-6-sun-1.6.0.00/jre/…
os.arch=i386
java.io.tmpdir=/tmp
line.separator=java.vm.specification.vendor=Sun Microsystems Inc.
os.name=Linux
sun.jnu.encoding=UTF-8
java.library.path=/usr/lib/jvm/java-6-sun-1.6.0.00/jre/…
java.specification.name=Java Platform API Specification
java.class.version=50.0
sun.management.compiler=HotSpot Server Compiler
os.version=2.6.20-16-generic
user.home=/home/export/silveira
user.timezone=
java.awt.printerjob=sun.print.PSPrinterJob
file.encoding=UTF-8
java.specification.version=1.6
user.name=silveira
java.class.path=.
java.vm.specification.version=1.0
sun.arch.data.model=32
java.home=/usr/lib/jvm/java-6-sun-1.6.0.00/jre
java.specification.vendor=Sun Microsystems Inc.
user.language=pt
java.vm.info=mixed mode
java.version=1.6.0
java.ext.dirs=/usr/lib/jvm/java-6-sun-1.6.0.00/jre/…
sun.boot.class.path=/usr/lib/jvm/java-6-sun-1.6.0.00/jre/…
java.vendor=Sun Microsystems Inc.
file.separator=/
java.vendor.url.bug=http://java.sun.com/cgi-bin/bugreport…
sun.cpu.endian=little
sun.io.unicode.encoding=UnicodeLittle
sun.cpu.isalist=
Try out at your home. 🙂
An side-scrolling game attempt.
I used two images, this mountain background made with Gimp (xcf sources here) and that ship above made with Inkscape (svg sources here).
import javafx.ui.*;
import javafx.ui.canvas.*;
var scroll;
scroll = [1..800] dur 60000 linear continue if true;
var mountains = Clip{
transform: bind translate(-scroll,0)
shape: Rect {x:bind scroll, y:0, width:400, height:200}
content: [ImageView {
transform: translate(0,0)
image: Image { url: "http://silveiraneto.net/downloads/mountains.png"}
},
ImageView {
transform: translate(800,0)
image: Image { url: "http://silveiraneto.net/downloads/mountains.png"}
}
]
};
var h = 50;
var ship = ImageView {
cursor: HAND
transform: bind translate(0,h)
image: Image { url: "http://silveiraneto.net/downloads/jfx_plane.png"}
onMouseDragged: operation(e) {
h += e.localDragTranslation.y;
}
};
Canvas {
content: [mountains, ship]
}