Master Groovy List Operations: From Java to Powerful Scripting

In the previous article the author showed how Java code can be transformed into Groovy. This follow‑up demonstrates Groovy’s native support for list operations.

First, a Java class that filters a list of names longer than three characters is presented. The class contains a filter method and a main method that builds an ArrayList, adds four names, calls filter, and prints the results.

package com.fun;

import com.fun.frame.httpclient.FanLibrary;
import org.slf4j.Logger;

class TSSS extends FanLibrary {
    public static Logger logger = getLogger(TSSS.class);

    public static void main(String[] args) {
        List names = new ArrayList();
        names.add("Ted");
        names.add("Fred");
        names.add("Jed");
        names.add("Ned");
        List shortNames = filter(names, 3);
        output(shortNames.size());
        for (Iterator i = shortNames.iterator(); i.hasNext();) {
            String s = (String) i.next();
            output(s);
        }
    }

    public static List filter(List strings, int length) {
        List result = new ArrayList();
        for (String str : strings) {
            if (str.length() < length + 1) {
                result.add(str);
            }
        }
        return result;
    }
}

Using Arrays.asList() the same logic can be written more concisely in Java, but the article then rewrites the program as a Groovy script, dropping the class and static typing.

List names = new ArrayList()
names.add("Ted")
names.add("Fred")
names.add("Jed")
names.add("Ned")
List shortNames = filter(names, 3)
println shortNames.size()
for (String s : shortNames) {
    println s
}

def filter(List strings, int length) {
    List result = new ArrayList()
    for (String str : strings) {
        if (str.length() < length + 1) {
            result.add(str)
        }
    }
    return result
}

Groovy further simplifies list handling with literal syntax. A list can be created with def names = [] or populated directly: def names = ["Ted", "Fred", "Jed", "Ned"]. Elements are accessed and modified via the index operator, e.g., assert names[1] == "Fred" and names[1] = "Frederic".

Groovy also decorates core JDK collections with convenient methods such as each() for iteration, findAll() for filtering, and predicates like any and every. Example usage:

println names.any { it.length() > 3 }
println names.every { it.length() > 3 }
println names.find { it.length() > 3 }
println names.findAll { it.length() > 2 }