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Tag: code

NumberFormatException Example

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

Java Duke animated gif waving

Pointers to functions in C++

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);
}

Simple Java Chronometer

A very simple Java chronometer code (inspired in the chronometer code in Opale project) you can use for simples measures.

In the main method there’s a example of use.

public final class Chronometer{
    private long begin, end;
 
    public void start(){
        begin = System.currentTimeMillis();
    }
 
    public void stop(){
        end = System.currentTimeMillis();
    }
 
    public long getTime() {
        return end-begin;
    }
 
    public long getMilliseconds() {
        return end-begin;
    }
 
    public double getSeconds() {
        return (end - begin) / 1000.0;
    }
 
    public double getMinutes() {
        return (end - begin) / 60000.0;
    }
 
    public double getHours() {
        return (end - begin) / 3600000.0;
    }
 
    public static void main(String[] arg) {
        Chronometer ch = new Chronometer();
 
        ch.start();
        for (int i = 1;i<10000000;i++) {}
        ch.stop();
        System.out.println(ch.getTime());
 
        ch.start();
        for (int i = 10000000;i>0;i--) {}
        ch.stop();
        System.out.println(ch.getTime());
    }
}

Compiling and running this code gives you something like:

191
12

Maybe you got surprised with this. The first loop, with 10 millions of steps is slower than the second, also with 10 millions of steps.

Why?

Some processors (like x86) have an zero-flag in their ALU. Using it is faster perform the question i≠0 than i<K (for a K≠0). In a loop with 10 millions iterations this difference can be perceptible. And this is not just for Java. You can try those loops in others language and see this behavior.

Think twice next time you write a big loop. :)

Java, listing system properties

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. :)