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General Java Questions II
the array[].length but it does not work, how can I solve this problem?
Answer: Java doesn't really have "multidimensional arrays", only arrays of arrays. So
try: array[0].length and you will get this dimension.
I guess what I'm asking is "Is java.util.Hashtable thread safe?"
Q: It's been a while since I've used hashtables for anything significant, but I seem to
recall the get() and put() methods being synchronized.
The JavaDocs don't reflect this. They simply say that the class Hashtable is
synchronized. What can I assume? If several threads access the hashtable at the
same time (assuming they are not modifying the same entry), the operations will
succeed, right? I guess what I'm asking is "Is java.util.Hashtable thread safe?"
Answer: That is right! It is recommendable, if you have questions like these, always
look at source for the API, it's freely available.
Q: I try to copy an object of my own using the clone() method from
java.lang.Object, but this is a protected method so I can't use it. Is there some other
way to get my objective of duplicating an arbitrary object?
Answer: If you want to clone your object, you need to make it cloneable. To achieve
this, you need to do two things:
1. implement the interface Cloneable
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;
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