how to set default method argument values?

Question

Hi,

Is it possible to set the default method parameter values in Java?

Example: If there is a method

public int doSomething(int arg1, int arg2)
{
//some logic here
 return 0;
}

is it possible to modify the given method in order to be able to call it with and without parameters?

example:

doSomething(param1, param2);
doSomething();

Thanks!

Answer 1

No. Java doesn't support default parameters like C++. You need to define a different method:

public int doSomething()
{
   return doSomething(value1, value2);
}

Answer 2

You can accomplish this via method overloading.

public int doSomething(int arg1, int arg2)
{
        return 0;
}

public int doSomething()
{
        return doSomething(defaultValue0, defaultValue1);
}

By creating this parameterless method you are allowing the user to call the parameterfull method with the default arguments you supply within the implementation of the parameterless method. This is known as overloading the method.

Answer 3

You can't declare default values for the parameters like C# (I believe) lets you, but you could simply just create an overload.

public int doSomething(int arg1, int arg2) {
    //some logic here
    return 0;
}

//overload supplies default values of 1 and 2
public int doSomething() {
    return doSomething(1, 2);
}

If you are going to do something like this please do everyone else who works with your code a favor and make sure you mention in Javadoc comments what the default values you are using are!

Answer 4

You can overload the method with different parameters:

public int doSomething(int arg1, int arg2)
{
//some logic here
        return 0;
}

public int doSomething(
{
doSomething(0,0)
}

Answer 5

If your arguments are the same type you could use varargs:

public int something(int... args) {
    int a = 0;
    int b = 0;
    if (args.length > 0) {
      a = args[0];
    }
    if (args.length > 1) {
      b = args[1];
    }
    return a + b
}

but this way you lose the semantics of the individual arguments, or

have a method overloaded which relays the call to the parametered version

public int something() {
  return something(1, 2);
}

or if the method is part of some kind of initialization procedure, you could use the builder pattern instead:

class FoodBuilder {
   int saltAmount;
   int meatAmount;
   FoodBuilder setSaltAmount(int saltAmount) {
       this.saltAmount = saltAmount;
       return this;
   }
   FoodBuilder setMeatAmount(int meatAmount) {
       this.meatAmount = meatAmount;
       return this;
   }
   Food build() {
       return new Food(saltAmount, meatAmount);
   }
}

Food f = new FoodBuilder().setSaltAmount(10).build();
Food f2 = new FoodBuilder().setSaltAmount(10).setMeatAmount(5).build();

Then work with the Food object

int doSomething(Food f) {
    return f.getSaltAmount() + f.getMeatAmount();
}

The builder pattern allows you to add/remove parameters later on and you don't need to create new overloaded methods for them.

Answer 6

It's not possible to default values in Java. My preferred way to deal with this is to overload the method so you might have something like:

public class MyClass
{
  public int doSomething(int arg1, int arg2)
  {
    ...
  }

  public int doSomething()
  {
    return doSomething(<default value>, <default value>);
  }
}