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Java Function/Constructor Overloading Puzzle

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  • Difficulty Level : Expert
  • Last Updated : 03 Sep, 2018

Predict the output of the program

public class GFG {
    private GFG(Object o) {
    private GFG(double[] d) {
        System.out.println("double array");
    public static void main(String[] args) {
        new GFG(null);

The parameter passed to the constructor is the null object reference and arrays are reference types too. If we try running the program, we get following.
The program prints double array.

We can notice that the compiler doesn’t cause ambiguous call error. Java’s overload resolution process operates in two phases.
The first phase selects all the methods or constructors that are accessible and applicable.
The second phase selects the most specific of the methods or constructors selected in the first phase. One method or constructor is less specific than another if it can accept any parameters passed to the other.
In our program, both constructors are accessible and applicable. The constructor GFG(Object) accepts any parameter passed to GFG(double[]), so GFG(Object) is less specific. (Every double array is an Object, but not every Object is a double array.)

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