groovy/groovy-core/xdocs/beans.wiki

1 Groovy Beans

GroovyBeans are JavaBeans but using a much simpler syntax. 
Here's an example 

{code:gsh}
import java.util.Date

class Customer {
    // properties
    Integer id
    String name
    Date dob
    
    // sample code
    static void main(args) {
        customer = new Customer(id:1, name:"Gromit", dob:new Date())
        println("Hello ${customer.name}")
    }
}
{code}
{code:output}
Hello Gromit
{code}

Notice how the properties look just like public fields. You can also set
named properties in a bean constructor in Groovy. In Groovy fields and properties
have been merged so that they act and look the same. So the above is equivlent to the
following Java code...

{code:java}
import java.util.Date;

public class Customer {
    // properties
    private Integer id;
    private String name;
    private Date dob;
    
    public Integer getId() {
        return id;
    }
    
    public Integer getId() {
        return id;
    }
    
    public Integer getId() {
        return id;
    }
    
    public void setId(Integer id) {
        this.id = id;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public void setDob(Date dob) {
        this.dob = dob;
    }
    
    // sample code
    public static void main(String[] args) {
        Customer customer = new Customer();
        customer.setId(1);
        customer.setName("Gromit");
        
        println("Hello " + customer.getName());
    }
}
{code}

1.1 Property and field rules

When Groovy is compiled to bytecode the following rules are used.

- if the property is private, then a Java field is used to represent the property
- if a public or protected property is declared (properties are public by default) then a public or protected getter and setter are created along with a private Java field
- if you don't declare any getters or setters they are automatically created for you at the bytecode level for public or protected properties. 
- if you create a public or protected property you can overload any auto-created methods

So for example you could create a public read only property with a protected setter
or a read only property like this

{code:gsh}
class Foo {
    // read only property
    private String name
    public String getName() { return name }
    
    // read only property with protected setter
    Integer amount
    protected void setAmount(Integer amount) { this.amount = amount }
    
    // dynamically typed property
    cheese
}
{code}