Step‑by‑Step Evolution of a Hello World Program from Java to Groovy

Groovy and Java are closely related languages with very similar syntax, so Java developers can learn Groovy easily; most Java programs are also valid Groovy programs simply by renaming the file extension from .java to .groovy .

The article starts with a basic Hello World Java program and shows how it evolves into Groovy through a series of incremental transformations.

Original Hello World

public class HelloWorld {

    private String name;

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public String greet() {
        return "Hello " + name;
    }

    public static void main(String[] args) {
        HelloWorld helloWorld = new HelloWorld();
        helloWorld.setName("Groovy");
        System.out.println(helloWorld.greet());
    }
}

The class defines a private name field with its getter and setter, a greet() method that returns the greeting string, and a main() method that creates an instance, sets the name, and prints the greeting.

Groovy Program – First Evolution

public class HelloWorld {

    private String name;

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public String greet() {
        return "Hello " + name;
    }

    public static void main(String[] args) {
        HelloWorld helloWorld = new HelloWorld()
        helloWorld.setName("Groovy")
        System.out.println(helloWorld.greet());
    }
}

At this stage the Groovy code is identical to the Java version; no Groovy‑specific features have been applied yet.

Groovy Program – Second Evolution

We begin “Groovy‑ifying” the program by removing semicolons and the public keyword, which are optional in Groovy.

class HelloWorld {

    private String name

    void setName(String name) {
        this.name = name
    }

    String getName() {
        return name
    }

    String greet() {
        return "Hello " + name
    }

    static void main(String[] args) {
        HelloWorld helloWorld = new HelloWorld()
        helloWorld.setName("Groovy")
        System.out.println(helloWorld.greet())
    }
}

Groovy Program – Third Evolution

Groovy’s GString allows embedding variables directly in double‑quoted strings, so the greet() method can use "Hello ${name}" instead of concatenation.

String greet() {
    return "Hello ${name}"
}

Groovy Program – Fourth Evolution

When the last expression in a method is the value to return, the return keyword can be omitted, making the method even shorter.

class HelloWorld {

    private String name

    void setName(String name) {
        this.name = name
    }

    String getName() {
        name
    }

    String greet() {
        "Hello ${name}"
    }

    static void main(String[] args) {
        HelloWorld helloWorld = new HelloWorld()
        helloWorld.name = "Groovy"
        System.out.println(helloWorld.greet())
    }
}

Both getName() and greet() are now single‑line methods.

Groovy Program – Fifth Evolution

Groovy automatically provides a private field and its getter/setter for a simple property declaration, so we can write String name without explicitly defining the field.

class HelloWorld {

    String name

    String greet() {
        "Hello ${name}"
    }
}

def helloWorld = new HelloWorld()
helloWorld.name = "Groovy"
println helloWorld.greet()

Groovy Program – Sixth Evolution

Groovy adds convenient shortcuts such as using println instead of System.out.println() and allowing omission of parentheses for top‑level method calls.

class HelloWorld {

    String name

    String greet() {
        "Hello ${name}"
    }

    static void main(String[] args) {
        HelloWorld helloWorld = new HelloWorld()
        helloWorld.name = "Groovy"
        println helloWorld.greet()
    }
}

Groovy Program – Seventh Evolution

Groovy supports dynamic typing, so we can replace explicit types with def and even omit the return type of main .

class HelloWorld {

    def name

    def greet() {
        "Hello ${name}"
    }

    static main(args) {
        def helloWorld = new HelloWorld()
        helloWorld.name = "Groovy"
        println helloWorld.greet()
    }
}

Groovy Program – Eighth Evolution

Because Groovy is also a scripting language, we can drop the main method entirely and write a script that directly creates an instance and prints the greeting.

class HelloWorld {

    def name

    def greet() {
        "Hello ${name}"
    }
}

def helloWorld = new HelloWorld()
helloWorld.name = "Groovy"
println helloWorld.greet()

The article concludes with a disclaimer about original publication and a list of other technical articles.