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Presentation
Question

Answer

Tags

#bloch-effective-java-2ed #java

Question

Suppose we have a class


public class Point {
    private final int x;
    private final int y;

    @Override public boolean equals(Object o) {
	if (!(o instanceof Point))
	    return false;
	Point p = (Point)o;
	return p.x == x && p.y == y;
    }
    // Remainder omitted
}

and a subclass

public class ColorPoint extends Point {
    private final Color color;

    @Override public boolean equals(Object o) {
      if (!(o instanceof ColorPoint))
         return false;
      return super.equals(o) && ((ColorPoint) o).color == color;
     }

    // Remainder omitted
}

what are the consequences of implementing equals() method on ColorPoint like above?

Answer

It violates symmetry. You get different results when comparing a point to a color point and vice versa.

Tags

#bloch-effective-java-2ed #java

Question

Suppose we have a class


public class Point {
    private final int x;
    private final int y;

    @Override public boolean equals(Object o) {
	if (!(o instanceof Point))
	    return false;
	Point p = (Point)o;
	return p.x == x && p.y == y;
    }
    // Remainder omitted
}

and a subclass

public class ColorPoint extends Point {
    private final Color color;

    @Override public boolean equals(Object o) {
      if (!(o instanceof ColorPoint))
         return false;
      return super.equals(o) && ((ColorPoint) o).color == color;
     }

    // Remainder omitted
}

what are the consequences of implementing equals() method on ColorPoint like above?

Answer

Tags

#bloch-effective-java-2ed #java

Question

Suppose we have a class


public class Point {
    private final int x;
    private final int y;

    @Override public boolean equals(Object o) {
	if (!(o instanceof Point))
	    return false;
	Point p = (Point)o;
	return p.x == x && p.y == y;
    }
    // Remainder omitted
}

and a subclass

public class ColorPoint extends Point {
    private final Color color;

    @Override public boolean equals(Object o) {
      if (!(o instanceof ColorPoint))
         return false;
      return super.equals(o) && ((ColorPoint) o).color == color;
     }

    // Remainder omitted
}

what are the consequences of implementing equals() method on ColorPoint like above?

Answer

It violates symmetry. You get different results when comparing a point to a color point and vice versa.

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pdfs

owner: piotr.wasik - (no access) - Effective Java (Joshua Bloch), 2ed, p37
owner: Jack-Rustier - (no access) - Joshua Bloch-Effective Java-Addison-Wesley (2017).pdf, p62

Summary

status	not learned	measured difficulty	37% [default]	last interval [days]
repetition number in this series	0	memorised on		scheduled repetition
scheduled repetition interval		last repetition or drill

Details

No repetitions

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