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Eduardo Jiménez
Asked: 2022-05-27 12:46:18 +0800 CST 2022-05-27 12:46:18 +0800 CST

Java: Create methods with default values

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There are languages ​​like javascript which accept that their functions have a default value. For example:

function times(number = 3, mult = 2) {
    return number * mult;
}

times();                // --> 6
times(5);               // --> 10
times(undefined, 4);    // --> 12
times(5, 3);            // --> 15

Is it possible to achieve this behavior in Java?

java

1 Answers

  1. Best Answer

    Although in Java there is no concept as such, the concept of default parameters can implement method overloading , which allows us to have the same method with different parameters.

    What should be done is to consider each case:

    public class Main {

    public static void main(String[] args) {

        System.out.println(times());
        System.out.println(times(5));
        System.out.println(times(null, 4));
        System.out.println(times(5, 3));

    }

    // No params
    private static double times() {
        return times(3, 2);
    }
    // Just the first param
    private static double times(double a) {
        return times(a, 2);
    }
    // Just the second param
    private static double times(Double a, double b) {
        return times(3, b);
    }
    // The two params
    private static double times(double a, double b) {
        return a * b;
    }
}

    As you can see, it times(Double a, double b)is used when the first argument does not exist, however this is because you are working with a primitive data type. Ideally, the implementation should be similar to this:

    private static void customMethod() {
    customMethod(default_1, default_2);
}

private static void customMethod(CustomObject a) {
    customMethod(a, default_2);
}

private static void customMethod(CustomObject a, CustomObject b) {
    // Just the second param
    if (null == a) {
        a = default_1;
    } 

    /* Tu código con ambos parámetros va aquí*/
    
}

    Another way to achieve the same behavior is with a Fluent Interface , which works similarly to a sequence of setters, only that they return the same object they belong to.

    public class Main {

    public static void main(String[] args) {

        System.out.println(new Times().times());
        System.out.println(new Times().setFirstNumber(5).times());
        System.out.println(new Times().setSecondNumber(4).times());
        System.out.println(new Times().setFirstNumber(5).setSecondNumber(3).times());

    }

    private static class Times {
        private double first_number = 3;
        private double second_number = 2;

        public Times setFirstNumber(double number) {
            this.first_number = number;
            return this;
        }

        public Times setSecondNumber(double number) {
            second_number = number;
            return this;
        }

        public double times() {
            return this.first_number * this.second_number;
        }
    }

}

    I personally think that the FluentInterface design is much more scalable and useful for this type of case.

    • 2