330 Java Tips.pdf - FTP Server

General Java Questions I
2. override the method clone(), so that it
a. becomes public
b. calls super.clone()
c. if necessary, clones any members, or
d. if a member can't be cloned, creates a new instance.
Simple example:
public MyClass implements Cloneable {
int someNumber;
String someString;
public Object clone() {
// primitives and Strings are no
// problem
return super.clone();
}
}
In this case the method clone() of the class MyClass returns a new instance of
MyClass, where all members have exactly the same value. That means, the object
reference 'someString' points to the same object. This is called a shallow
copy. In many cases this is no problem. Strings are immutable and you do not
need a new copy. But if you need new copies of members, you have to do it in
the clone() method. Here is another simple example:
public class SomeMember implements Cloneable {
long someLong;
}
public Object clone() {
return super.clone();
}
public AnotherClass extends MyClass {
SomeMember someMember;
}
public Object clone() {
AnotherClass ac = (AnotherClass)(super.clone());
if (someMember != null) {
ac.someMember = (SomeMember)(someMember.clone());
}
return ac;
}
Note that the class AnotherClass, that extends MyClass, automatically becomes
Cloneable, because MyClass is Cloneable.
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