Overloading Methods and Constructors

One very interesting property of Java is how it allows you to define methods that have the same conceptual functionality as each other by using the same name but changing either the type or number of parameters. Let's see how this could work.

class Age {

    public double a = 0;

    public void setAge ( double _a ) {

        a = _a;

    }

    public void setAge ( int year, int month ) {

        a = year + (double) month / 12;

    }

    public double getAge () {

        return a;

    }

}

class Example09 {

    public static void main(String[] args) {

        Age age = new Age();

        age.setAge(12.5);

        System.out.println(age.getAge());

        age.setAge(9, 3);

        System.out.println(age.getAge());

    }

}

Note

Look at the highlighted portion in the preceding code. As we are taking the integer parameter month and dividing it by a number, the result of the operation will be a double. To avoid possible errors, you need to convert the integer into a floating comma number. This process, called casting, is done by adding the new type between brackets in front of the object, variable, or operation we want to convert.

The result of this example is:

12.5

9.25

Process finished with exit code 0

This shows that both methods modify the a variable in the Age class by taking different sets of parameters. This same mechanism for having conceptually equivalent results from different blocks of code can be used for the constructors of a class, as shown in the following example.

class Age {

    public double a = 0;

    Age ( double _a ) {

        a = _a;

    }

    Age ( int year, int month ) {

        a = year + (double) month / 12;

    }

    public double getAge () {

        return a;

    }

}

class Example10 {

    public static void main(String[] args) {

        Age age1 = new Age(12.5);

        Age age2 = new Age(9, 3);

        System.out.println(age1.getAge());

        System.out.println(age2.getAge());

    }

}

In this case, as a way to show the functionality, instead of instantiating a single object and calling the different methods to modify its variables, we had to create two different objects, age1 and age2, with one or two parameters, as those are the possible options offered by the constructors available in the Age class.