Object clone method

/*Creates and returns a copy of this object. The precise meaning of "copy" may depend on the class of the object. The general intent is that, for any object x, the expression:  x.clone() != xwill be true, and that the expression:  x.clone().getClass() == x.getClass()will be true, but these are not absolute requirements. While it is typically the case that:  x.clone().equals(x)will be true, this is not an absolute requirement. By convention, the returned object should be obtained by calling super.clone. If a class and all of its superclasses (except Object) obey this convention, it will be the case that x.clone().getClass() == x.getClass(). By convention, the object returned by this method should be independent of this object (which is being cloned). To achieve this independence, it may be necessary to modify one or more fields of the object returned by super.clone before returning it. Typically, this means copying any mutable objects that comprise the internal "deep structure" of the object being cloned and replacing the references to these objects with references to the copies. If a class contains only primitive fields or references to immutable objects, then it is usually the case that no fields in the object returned by super.clone need to be modified. The method clone for class Object performs a specific cloning operation. First, if the class of this object does not implement the interface Cloneable, then a CloneNotSupportedException is thrown. Note that all arrays are considered to implement the interface Cloneable. Otherwise, this method creates a new instance of the class of this object and initializes all its fields with exactly the contents of the corresponding fields of this object, as if by assignment; the contents of the fields are not themselves cloned. Thus, this method performs a "shallow copy" of this object, not a "deep copy" operation. The class Object does not itself implement the interface Cloneable, so calling the clone method on an object whose class is Object will result in throwing an exception at run time.*/protected native Object clone() throws CloneNotSupportedException;

 

1 none of the following requirements must be met:

X. Clone ()! = X // For example, return this in the Colne method of the subclass;

X. clone (). getclass () = x. getclass () // sub-class implements the clone method, and super is not called. clone, but a new subclass object, this is not the same class

X. Clone (). Equals (x) // subclass implements the Colne method. If the field used by equals is modified, it is obviously not equal.

2. According to the Convention, the clone method implemented by the subclass should call super. clone (), and its parent class also complies with this Convention, then X. clone (). getclass () = x. getclass ()

3. In practice, cloning and itself should be independent of each other, totally two things, X. clone (). equals (x) should return false. To achieve this effect, you must call super. after cloning (), modify the variable object reference contained in the cloned object. These variable objects need to be copied in depth.

4. If a class only contains immutable objects and native types, you do not need to modify the field after super. Clone () is called.

5. The cloneclass class that implements the clone function implements the cloneable interface. Otherwise, clonenotsupportedexception will be thrown.

6. the clone () method is overloaded. Finally, super is called in the clone () method. clone (), which also means no matter what the clone class's inheritance structure is, super. clone () directly or indirectly calls Java. lang. object Class clone () method. The following is a detailed explanation of these points. The third point is the most important. Take a closer look at the clone () native method of the object class. The efficiency of the native method is generally much higher than that of the non-native method in Java. This also explains why to use the clone () method in the object instead of adding a new class, and then assigning the information in the original object to the new object, although this also achieves
Clone function. For the second point, you should also observe whether the clone () in the object class is a protected attribute method. This also means that if you want to apply the clone () method, you must inherit the object class. All classes in Java inherit the object class by default, so you don't need to care about this.

7. To allow other classes to call the clone () method of the clone class, set the attribute of the clone () method to public after the overload. ,