Groovy: Methods

Methods in Groovy are defined with a return type or with the def keyword. If a method is defined with specific type, then it should return the value of that type only.

HelloWorld.groovy

int fact(n){
 if(n == 0 || n == 1) return 1
 
 return n * fact(n-1)
}

int result = fact(5)

println "Factorial of 5 is $result"

Output

Factorial of 5 is 120

In the above example, I defined a method ‘fact’ which takes an integer as input and return an integer value as output.

If you make the return type of the method as def, then you can return value of any type.

HelloWorld.groovy

def getMeSomeData(int a){

 if(a == 1){
  return 101
 }
 
 if(a == 2){
  return "You entered 2"
 }
 
 if(a==3){
  return true
 }
 
 if(a==4){
  return 3.14
 }
 
 return null
}

println "getMeSomeData(0) : ${getMeSomeData(0)}"
println "getMeSomeData(1) : ${getMeSomeData(1)}"
println "getMeSomeData(2) : ${getMeSomeData(2)}"
println "getMeSomeData(3) : ${getMeSomeData(3)}"
println "getMeSomeData(4) : ${getMeSomeData(4)}"

Output

getMeSomeData(0) : null

getMeSomeData(1) : 101

getMeSomeData(2) : You entered 2

getMeSomeData(3) : true

getMeSomeData(4) : 3.14

If you do not return a value explicitly from the method, then the value evaluated in the last line executed will be returned.

HelloWorld.groovy

def getMeSomeData(int a){

 tempResult = null
 
 if(a == 1){
  tempResult = 101
 }
 
 if(a == 2){
  tempResult = "You entered 2"
 }
 
 if(a==3){
  tempResult = true
 }
 
 if(a==4){
  tempResult = 3.14
 }
 
 finalResult = tempResult
}

println "getMeSomeData(0) : ${getMeSomeData(0)}"
println "getMeSomeData(1) : ${getMeSomeData(1)}"
println "getMeSomeData(2) : ${getMeSomeData(2)}"
println "getMeSomeData(3) : ${getMeSomeData(3)}"
println "getMeSomeData(4) : ${getMeSomeData(4)}"

Output

getMeSomeData(0) : null

getMeSomeData(1) : 101

getMeSomeData(2) : You entered 2

getMeSomeData(3) : true

getMeSomeData(4) : 3.14

You can even omit type of a parameter in method definition.

HelloWorld.groovy

def sum(a, b){
 return a + b
}

println "sum(10, 20) : ${sum(10, 20)}"
println "sum(10.1, 20.1) : ${sum(10.1, 20.1)}"
println "sum('Hello', ' World') : ${sum('Hello', ' World')}"

Output

sum(10, 20) : 30

sum(10.1, 20.1) : 30.2

sum('Hello', ' World') : Hello World

As you see the definition of sum method, I do not specified the argument types, it is decided at run time.

For example, I updated above snippet to print the argument class names.

HelloWorld.groovy

def sum(a, b){
 println "${a.class}, ${b.class}"
 return a + b
}

println "sum(10, 20) : ${sum(10, 20)}"
println "sum(10.1, 20.1) : ${sum(10.1, 20.1)}"
println "sum('Hello', ' World') : ${sum('Hello', ' World')}"

Output

class java.lang.Integer, class java.lang.Integer

sum(10, 20) : 30

class java.math.BigDecimal, class java.math.BigDecimal

sum(10.1, 20.1) : 30.2

class java.lang.String, class java.lang.String

sum('Hello', ' World') : Hello World

Points to Remember

a.   If you do not specify the access specifier (public, private, protected and default), then the method is public by default.

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