Groovy: Constructor invocation

There are four ways to invoke the constructor.

a.   Normal Java way using new operator

b.   Using coercion with as keyword

c.    Using coercion in assignment

d.   Using named parameters

For example, take below Employee class, I defined one constructor that takes employee name and id as arguments.

class Employee{

         String name

         int id

         Employee(name, id){

                  this.name = name

                  this.id = id

         }

        

}

Using new operator

Employee emp1 = new Employee("Krishna", 123)

Using coercion with as keyword

Employee emp2 = ["Krishna", 123] as Employee

Using coercion in assignment

Employee emp3 = ["Krishna", 123]

Find the below working application.

HelloWorld.groovy

class Employee{
 String name
 int id

 Employee(name, id){
  this.name = name
  this.id = id
 }
 
}

Employee emp1 = new Employee("Krishna", 123)
Employee emp2 = ["Krishna", 123] as Employee
Employee emp3 = ["Krishna", 123]

void printEmployee(Employee emp){
 println "name: ${emp.name}, id: ${emp.id}"
}

printEmployee(emp1)
printEmployee(emp2)
printEmployee(emp3)

Output

name: Krishna, id: 123

name: Krishna, id: 123

name: Krishna, id: 123

Using named parameters

If a class has default constructor, then you can create objects by passing parameters in the form of a map (property/value pairs)

HelloWorld.groovy

class Employee{
 String name
 int id
}

Employee emp1 = new Employee(name : "Krishna", id : 123)
Employee emp2 = new Employee(name : "Krishna")
Employee emp3 = new Employee()


void printEmployee(Employee emp){
 println "name: ${emp.name}, id: ${emp.id}"
}

printEmployee(emp1)
printEmployee(emp2)
printEmployee(emp3)

Output

name: Krishna, id: 123

name: Krishna, id: 0

name: null, id: 0

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