Set Question : Bad equals override.

[Tom Scott]

The code as posted seems to work fine, output is a unique set of elements.

However if I replace the Statement B equals method with the commented out Statement A equals method I get a stack overflow error. I can see that the commented out equals method is not a proper override but don't understand why it causes a stack overflow. Can anyone explain?

Thanks in advance,
Tom

package ex1_football_sticker;
import java.util.*;
 
public class FootballSticker {
    
    private String name;
    private int year;
    
    /** Creates a new instance of FootballSticker */
    public FootballSticker(String name, int year) {
        this.name = name;
        this.year = year;
    }
    public static void test1() {
       FootballSticker[] stickers = { new FootballSticker("Bertie",1980), 
                                     new FootballSticker("Casey",1981),
                                     new FootballSticker("Davey",1981),
                                     new FootballSticker("Arnie",1981),
                                     new FootballSticker("Davey",1981),
                                     new FootballSticker("Eddie",1980) }    ;
       
       Set set = new HashSet();
       for (FootballSticker i : stickers) {
           set.add(i);
       }
       System.out.println("Results:");
       Iterator iter = set.iterator();       
       while (iter.hasNext()) {
           System.out.println((FootballSticker)iter.next());
       }
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return year;
    }
    public void setAge(int year) {
        this.year = year;
    }
    public boolean equals(Object o) {
        // Statement A) Bad equals method
        // return (this.equals((FootballSticker)o));
        
        // Statement B) Good equals method
        return this.name.equals(((FootballSticker)o).name) && this.year ==((FootballSticker)o).year;           
    }
    public String toString() {
        return this.name + ":" + this.year;
    }
    public int hashCode() {
        return this.name.length() + this.year;
    }      
}
 

[Barry Gaunt]

Statement A makes a recursive call to the same equals method. So your program goes into a recursive loop and blows the stack.

[Tom Scott]

Thanks. Another attack of code blindness by me

[Barry Gaunt]

Originally posted by Tom Scott:
Thanks. Another attack of code blindness by me

Perfectly normal behavior for all of us javaheads, so don't too hard.