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Tags

#bloch-effective-java-2ed #equality #java

Question

Suppose we have a class that tries to cooperate with String. What is wrong with it?


public final class CaseInsensitiveString {

    private final String s;

    @Override public boolean equals(Object o) {
        if (o instanceof CaseInsensitiveString)
            return s.equalsIgnoreCase(((CaseInsensitiveString) o).s);
        if (o instanceof String)
            return s.equalsIgnoreCase((String) o);
       return false;
    }

    // rest of the code
}

Answer

It violates symmetry of equality - "BlaBla".equals(whatever) will do case-sensitive comparison, even if whatever is CaseInsensitiveString (in which case the result is false)

Tags

#bloch-effective-java-2ed #equality #java

Question

Suppose we have a class that tries to cooperate with String. What is wrong with it?


public final class CaseInsensitiveString {

    private final String s;

    @Override public boolean equals(Object o) {
        if (o instanceof CaseInsensitiveString)
            return s.equalsIgnoreCase(((CaseInsensitiveString) o).s);
        if (o instanceof String)
            return s.equalsIgnoreCase((String) o);
       return false;
    }

    // rest of the code
}

Answer

Tags

#bloch-effective-java-2ed #equality #java

Question

Suppose we have a class that tries to cooperate with String. What is wrong with it?


public final class CaseInsensitiveString {

    private final String s;

    @Override public boolean equals(Object o) {
        if (o instanceof CaseInsensitiveString)
            return s.equalsIgnoreCase(((CaseInsensitiveString) o).s);
        if (o instanceof String)
            return s.equalsIgnoreCase((String) o);
       return false;
    }

    // rest of the code
}

Answer

It violates symmetry of equality - "BlaBla".equals(whatever) will do case-sensitive comparison, even if whatever is CaseInsensitiveString (in which case the result is false)

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pdf

owner: piotr.wasik - (no access) - Effective Java (Joshua Bloch), 2ed, p35

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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