seeseemelk/MockBukkit

Many consider clone and Cloneable broken in Java, largely because the rules for overriding clone are tricky and difficult to get right, according to Joshua Bloch:

Object's clone method is very tricky. It's based on field copies, and it's "extra-linguistic." It creates an object without calling a constructor. There are no guarantees that it preserves the invariants established by the constructors. There have been lots of bugs over the years, both in and outside Sun, stemming from the fact that if you just call super.clone repeatedly up the chain until you have cloned an object, you have a shallow copy of the object. The clone generally shares state with the object being cloned. If that state is mutable, you don't have two independent objects. If you modify one, the other changes as well. And all of a sudden, you get random behavior.

A copy constructor or copy factory should be used instead.

This rule raises an issue when clone is overridden, whether or not Cloneable is implemented.

Noncompliant Code Example

public class MyClass {
  // ...

  public Object clone() { // Noncompliant
    //...
  }
}

Compliant Solution

public class MyClass {
  // ...

  MyClass (MyClass source) {
    //...
  }
}

See

• Copy Constructor versus Cloning

See Also

• {rule:java:S2157} - "Cloneables" should implement "clone"
• {rule:java:S1182} - Classes that override "clone" should be "Cloneable" and call "super.clone()"

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 70.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76