Home » If there are two constructors in a class and both hold a double value but for diffrent purposes? [closed]

If there are two constructors in a class and both hold a double value but for diffrent purposes? [closed]


which constructor will be assigned the value 200.0d.

Neither. The code will not compile.

I just want to know if somehow this situation arises

It can’t.

I can’t recommend it, but here is something you could do:

public class MathEquation {
    public MathEquation(Double d1, Double d2){
        if (d1 != null)
            number1 = d1;
        if (d2 != null)
            number2 = d2;
        if (d1==null && d2 == null)
            throw new IllegalArgumentException();

// construct with just numbber1
MathEquation e1 = new MathEquation(20.0, null);
// construct with just number2
MathEquation e2 = new MathEquation(null, 30.0);
// construct wit both number1 and number2
MathEquation e3 = new MathEquation(20.0, 30.0);

As described in the comments, you can’t do this. It simply won’t compile.

This is because overloads are resolved purely by class name, method name and parameter types. These constructors have the same class name, method name (constructors have the special name <init>) and parameter types, so they are overload equivalent. You can’t have two overload equivalent methods in a class.

You can do something similar to this using static factory methods (a static method, often in the same class, which returns an instance of the class):

public static MathEquation forNumber1(double number1){
    return new MathEquation(number1*2, 0);

public static MathEquation forNumber2(double number2){
    return new MathEquation(0, number2*2);

Provided you also define a constructor:

MathEquation(double number1, double number2) {
  this.number1 = number1;
  this.number2 = number2;

These are not overload equivalent because they have different method names. In fact, one of the advantages of static factory methods (Item 1 in Effective Java) is that they act like “named constructors”.

Then you simply invoke like any other static method:

MathEquation n1 = MathEquation.forNumber1(2);
MathEquation n2 = MathEquation.forNumber2(2);

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