...
By convention, the returned object should be obtained by calling
super.clone. If a class and all of its superclasses (exceptObject) obey this convention, it will be the case thatx.clone().getClass() == x.getClass().
Noncompliant Code Example
In this noncompliant code example, the clone() method in the class Base does not call super.clone(). Hence, the object devClone ends up being of type Base instead of Derived, with resulting incorrect application of the doLogic() method.
| Code Block | ||
|---|---|---|
| ||
class Base implements Cloneable {
public Object clone() throws CloneNotSupportedException {
return new Base();
}
protected void doLogic() {
System.out.println("Superclass doLogic");
}
}
class Derived extends Base {
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
protected void doLogic() {
System.out.println("Subclass doLogic");
}
public static void main(String[] args) {
Derived dev = new Derived();
try {
Base devClone = (Base)dev.clone(); // has type Base instead of Derived
devClone.doLogic(); // prints "Superclass doLogic" instead of "Subclass doLogic"
} catch (CloneNotSupportedException e) { /* ... */ }
}
}
|
Compliant Solution
This compliant solution correctly calls super.clone() in the Base class's clone() method.
| Code Block | ||
|---|---|---|
| ||
class Base implements Cloneable {
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
protected void doLogic() {
System.out.println("Superclass doLogic");
}
}
class Derived extends Base {
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
protected void doLogic() {
System.out.println("Subclass doLogic");
}
public static void main(String[] args) {
Derived dev = new Derived();
try {
Base devClone = (Base)dev.clone(); // has type Derived, as expected
devClone.doLogic(); // prints "Subclass doLogic", as expected
} catch (CloneNotSupportedException e) { /* ... */ }
}
}
|
Risk Assessment
Failing to call super.clone() may result in a cloned object having the wrong type, with resulting unexpected or incorrect results when it is used.
Guideline | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
MET55MET53-J JG | medium | probable | low | P12 | L1 |
Automated Detection
Automated detection is straightforward.
Bibliography
MET15-J. Do not use deprecated or obsolete classes or methods 05. Methods (MET) MET17-J. Do not increase the accessibility of overridden or hidden methods