123 lines
3.5 KiB
Plaintext
123 lines
3.5 KiB
Plaintext
== Why is this an issue?
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`Cloneable` is the marker `Interface` that indicates that `clone()` may be called on an object.
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Overriding `clone()` without implementing `Cloneable` can be helpful if you want to control how subclasses clone themselves, but
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otherwise, it's probably a mistake.
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The usual convention for `Object.clone()` according to Oracle's Javadoc is:
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. `x.clone() != x`
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. `x.clone().getClass() == x.getClass()`
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. `x.clone().equals(x)`
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Obtaining the object that will be returned by calling `super.clone()` helps to satisfy those invariants:
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. `super.clone()` returns a new object instance
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. `super.clone()` returns an object of the same type as the one `clone()` was called on
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. `Object.clone()` performs a shallow copy of the object's state.
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== How to fix it
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Ensure that the `clone()` method calls `super.clone()` and implement `Cloneable` in the class or remove the clone method.
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=== Code examples
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==== Noncompliant code example
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[source,java,diff-id=1,diff-type=noncompliant]
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----
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class BaseClass { // Noncompliant - should implement Cloneable
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@Override
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public Object clone() throws CloneNotSupportedException { // Noncompliant - should return the super.clone() instance
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return new BaseClass();
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}
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}
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class DerivedClass extends BaseClass implements Cloneable {
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/* Does not override clone() */
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public void sayHello() {
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System.out.println("Hello, world!");
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}
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}
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class Application {
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public static void main(String[] args) throws Exception {
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DerivedClass instance = new DerivedClass();
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((DerivedClass) instance.clone()).sayHello(); // Throws a ClassCastException because invariant #2 is violated
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}
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}
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----
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==== Compliant solution
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[source,java,diff-id=1,diff-type=compliant]
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----
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class BaseClass implements Cloneable {
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@Override
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public Object clone() throws CloneNotSupportedException { // Compliant
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return super.clone();
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}
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}
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class DerivedClass extends BaseClass implements Cloneable {
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/* Does not override clone() */
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public void sayHello() {
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System.out.println("Hello, world!");
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}
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}
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class Application {
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public static void main(String[] args) throws Exception {
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DerivedClass instance = new DerivedClass();
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((DerivedClass) instance.clone()).sayHello(); // Displays "Hello, world!" as expected. Invariant #2 is satisfied
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}
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}
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----
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== Resources
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* https://cwe.mitre.org/data/definitions/580[MITRE, CWE-580] - clone() Method Without super.clone()
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* https://wiki.sei.cmu.edu/confluence/x/FjZGBQ[CERT, MET53-J.] - Ensure that the clone() method calls super.clone()
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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* Use super.clone() to create and seed the cloned instance to be returned.
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* Implement "Cloneable" in this class or remove the clone method.
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'''
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== Comments And Links
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(visible only on this page)
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=== is related to: S2975
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=== on 7 Aug 2013, 09:59:21 Freddy Mallet wrote:
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Is implemented by \http://jira.codehaus.org/browse/SONARJAVA-271
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=== on 7 Aug 2013, 13:20:27 Dinesh Bolkensteyn wrote:
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I fail to see why it would be mandatory to have the method throw the CloneNotSupportedException.
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You can perfectly catch and propagate (as an unchecked exception) the instance thrown by super.clone().
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So the PMD rule does not seem to make a lot of sense.
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In any case, I doubt that this method is mean to verify this, isn't it?
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=== on 8 Aug 2013, 06:27:34 Dinesh Bolkensteyn wrote:
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Thanks for the updates Ann!
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endif::env-github,rspecator-view[]
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