Productive programming with groovy - an introduction

Productive Programming with
Groovy
S G Ganesh
http://ocpjp7.blogspot.in

How I Felt Programming in Groovy vs.
Java!

Simple (first) Example
import java.io.*;
class Type {
public static void main(String []files) {
// process each file passed as argument
for(String file : files) {
// try opening the file with FileReader
try (FileReader inputFile = new FileReader(file)) {
int ch = 0;
while( (ch = inputFile.read()) != -1) {
// ch is of type int - convert it back to char
System.out.print( (char)ch );
}
} catch (FileNotFoundException fnfe) {
System.err.printf("Cannot open the given file %s ", file);
}
catch(IOException ioe) {
System.err.printf("Error when processing file %s; skipping it", file);
}
// try-with-resources will automatically release FileReader object
}
}
}
args.each { println new File(it).getText() }

Mere Syntactic Sugar?
Map<String, String> inglishWords = new HashMap<>();
inglishWords.put("Shampoo", "'Chapmo' (Hindi)");
inglishWords.put("Sugar", "'Sarkkarai' (Tamil)");
inglishWords.put("Copra", "'Koppara' (Malayalam)");
inglishWords.put("Jute", "'Jhuto' (Bengali)");
inglishWords.put("Cot", "'Khatva' (Sanskrit)");
for(Map.Entry<String, String> word : inglishWords.entrySet()) {
System.out.printf("%s => %s n", word.getKey(), word.getValue());
}
def inglishWords = [ "Shampoo" : "'Chapmo' (Hindi)",
"Sugar" : "'Sarkkarai' (Tamil)",
"Copra" : "'Koppara' (Malayalam)",
"Jute" : "'Jhuto' (Bengali)",
"Cot" : "'Khatva' (Sanskrit)" ]
inglishWords.each {
key, value ->
println "$key => $value"
}

Just Concise Expression?
System.out.println("The (key-based) sorted map is: ");
Map<String, String> keySortedMap = new TreeMap<>(inglishWords);
for(Map.Entry<String, String> word : keySortedMap.entrySet()) {
}
println "The (key-based) sorted map is: "
def keySortedMap = inglishWords.sort()
keySortedMap.each {
key, value ->
}

Now for the Real Magic! 
class MapUtil {
// this code segment from http://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java
public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue( Map<K, V> map ) {
List<Map.Entry<K, V>> list =
new LinkedList<Map.Entry<K, V>>( map.entrySet() );
Collections.sort( list, new Comparator<Map.Entry<K, V>>() {
public int compare( Map.Entry<K, V> o1, Map.Entry<K, V> o2 )
{
return (o1.getValue()).compareTo( o2.getValue() );
}
} );
Map<K, V> result = new LinkedHashMap<K, V>();
for (Map.Entry<K, V> entry : list) {
result.put( entry.getKey(), entry.getValue() );
}
return result;
}
}
System.out.println("The (value-based) sorted map is: ");
Map<String, String> valueSortedMap = MapUtil.sortByValue(inglishWords);
for(Map.Entry<String, String> word : valueSortedMap.entrySet()) {
}
println "The (value-based) sorted map is: "
def valueSortedMap = inglishWords.sort { it.value }
valueSortedMap.each {
key, value ->
}

HTML Creation Example
try (PrintWriter pw = new PrintWriter(new FileWriter("./index.java.html"))) {
pw.println("<html> <head> <title>Words from Indian origin in English</title> </head>
<body>");
pw.println("<h1>Words from Indian origin in English</h1>");
pw.println("<table border='1'> <tr> <th>Inglish word</th> <th>Origin</th></tr>");
pw.printf("<tr> <td> %s </td> <td> %s </td> </tr>", word.getKey(),
word.getValue());
}
pw.println("</table> <p style='font-style:italic;font-size:small;float:right'>Results obtained at
" + new Date() + "</p> </body> </html>");
}

HTML Creation Example
def writer = new StringWriter()
def doc = new MarkupBuilder(writer)
doc.html() {
head {
title("Words from Indian origin in English")
}
body {
h1("Words from Indian origin in English")
table(border:1) {
tr {
th("Inglish word")
th("Origin")
}
inglishWords.each { word, root ->
tr {
td("$word")
td("$root")
}
}
}
p(style:'font-style:italic;font-size:small;float:right', "Results obtained at ${new Date().dateTimeString}")
}
}
def filename = 'index.groovy.html'
new File(filename).write(writer.toString())

Not Convinced?! Check XML Creation
Example
try (PrintWriter pw = new PrintWriter(new FileWriter("./words.xml"))) {
pw.println("<inglishwords>");
pw.printf("t<language word='%s'> n tt <origin>
'%s'</origin> n t </language> n", word.getKey(), word.getValue());
}
pw.println("</inglishwords>");
}
xmlbuilder = new groovy.xml.MarkupBuilder()
xmlbuilder.inglishwords {
words.each { key, value ->
language(word:key) { origin(value) }
}
}

Where to Learn More About Groovy?

Some Dynamic Languages for .NET
World

Productive programming with groovy - an introduction

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