Question

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Why I’m getting StackOverflowError

I am using two classes: Date and Exam. Date sets a Date object from three integers: day, month,year; Exam sets an Exam object from one String courseName and one Date Object.

I am trying to run this code:

    public Exam(String name, Date d)
    {
        courseName=name;
        examDate=new Date(d);
    }

    //**a method that checks if two dates are equal**
    public boolean equals (Date r)
    {
        return (examDate.equals(r));
    }

    public static void main(String[] args)
    {
        Date d=new Date(11,11,2011);
        String a=new String("OOP");
        Exam b=new Exam(a,d);
        Date c=new Date(11,11,2011);
        System.out.println(b.equals(c));
    }

when I try to run the code I get the error Exception in thread “main” java.lang.StackOverflowError

The error says that the problem is on a line in Date class, which checks if two dates are equal:

public boolean equals (Date d)
{
    return (this.equals(d));
}

I’ll be thankful to know why that happens.

Answer 1

As James said, return (this.equals(d)); is definitely wrong. Supposing your Date class has attributes for year, month and day, you should rather try something like

public boolean equals(Object o) {
    if (! o instanceof Date) return false;
    Date d = (Date)o;
    return this.year == d.year && this.month == d.month && this.day == d.day;
}

Note it is important that the static type of the parameter is Object, see the answer of James