Class implements `Cloneable` but has not overridden the `clone` methodJAVA-S0046

This class implements Cloneable but does not define or use the clone method. This may be because This is a violation of the Cloneable contract, as stated in the JavaDocs:

By convention, classes that implement this interface should override Object.clone (which is protected) with a public method.

If other code attempts to clone an instance of this class, it may get an uninitialized or partially initialized version of the original object.

Examples

Problematic Code

class SomeClass implements Cloneable {

    public Object field1 = new Object();

    @Override
    public Object clone() {
        SomeClass cloned = null;
        
        try {
            cloned = (SomeClass)super.clone();

        } catch (CloneNotSupportedException e) {
            // ...
        }

        cloned.field1 = new Object();

        return cloned;
    }
}

class SomeOtherClass extends SomeClass implements Cloneable {

    public Object field2 = new Object();

    // No implementation of clone...

}


// Elsewhere...

SomeOtherClass a = new SomeOtherClass();
a.field2 = 3;

// ...

SomeOtherClass b = (SomeOtherClass)a.clone();

a.field1 != b.field1; // True
a.field2 != b.field2; // false?! This should not be false! - a contract violation.

Recommended

Define a clone method for the class to ensure that this does not occur:

class SomeOtherClass extends SomeClass implements Cloneable {

    public Object field2;

    // ...

    @Override
    public Object clone() {
        SomeOtherClass other = null
        
        
        try {
            other = (SomeOtherClass)super.clone();

        } catch (CloneNotSupportedException e) {
            // ...
        }

        other.field2 = new Object();
        return other;
    }

}

References

• Spotbugs - CN_IDIOM