10 Cloning
Cloning¶
creating an exact copy of an existing object in the memory
clone() from class java.lang.Object
Only objects of classes which implement Cloneable interface are eligible for cloning
By default, shallow copy occurs
| Shallow | Deep | |
|---|---|---|
| definition | custom clone() | |
| original and clone | dependent on each other | independent |
| changes | affect each other | no effect |
| preferred if object has | only primitive fields | references to other objects as fields |
| performance | faster and cheaper | slower and costlier |
Deep Copy¶
class Course implements Cloneable
{
String sub1, sub2, sub3;
// constructor
protected Object clone() throws CloneNotSupportedException
{
return super.clone();
}
}
class Student implements Cloneable
{
int id;
String name;
Course c;
// constructor
// this is what defines a deep copy
// without this, it will just be a shallow copy
protected Object clone() throws CloneNotSupportedException
{
Student s = (Student) super.clone();
student.c = (Course) c.clone();
return s;
}
}
class Tester
{
public static void main(String args[])
{
Course c = new Course("Phy", "Chem", "Bio");
Student s1 = new Student(111, "John", c);
Student s2 = null;
try {
s2 = (Student) s1.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
System.out.println(s1.c.sub3); // Bio
s2.course.sub3 = "Math"; // will not affect s1
}
}