Hi KC
Very nice observation, I confess always having some headaches myself
with this kind of code.
The Comparator (java.util.Comparator) is an interface. One can define
several comparators: one for String, another for Integer and so on. This
means several small classes, one per comparator.
Instead of doing so, there is this dirty trick that allows to have
everything in a sole class.
This is the dirty trick. Let's say you have a simple (a small number of
methods) interface (or abstract class):
// MyInterface.java
public interface MyInterface {
public String sayHello(String name);
}
You can avoid writing the classes implementing this interface and use
ad-hoc inline code, such as:
// Test.java
public class Test {
public static void main(String[] args){
*MyInterface my1 = new MyInterface(){ // The implementing
class defined here**
public String
sayHello(String name){ return "Hello " + name; }
};
MyInterface my2 = new MyInterface(){ // Another implementing
class defined here
public String
sayHello(String name){ return "Bonjour " + name; }
};*
String name = "Bond, James Bond";
System.out.println( my1.sayHello(name));
System.out.println( my2.sayHello(name));
}
}
With the dirty trick, it is possible to write only two java files
(MyInterface.java and Test.java). Without it I had to write two more
classes (with all the redundant heading code). It doesn't improve the
code readability, but allows to write less code (which is important for
a sample exercise).
In the case of the Comparator, the idea was to create a sole class file
containing a "factory" and keeping together all the comparators.
Hope it helps
mihai
kc a écrit :
Hi,
I am confused on how the Comparator interface is used in Execise 5.2
public static Comparator integerComparator() {
return new Comparator() {
public int compare(Object o1, Object o2) {
int val1 = ((Integer)o1).intValue();
int val2 = ((Integer)o2).intValue();
return (val1<val2 ? -1 : (val1==val2 ? 0 : 1));
}
};
}
instead of
public class MyComparator implements Comparator {
public int compare(Object o1, Object o2) {
int val1 = ((Integer)o1).intValue();
int val2 = ((Integer)o2).intValue();
return (val1<val2 ? -1 : (val1==val2 ? 0 : 1));
}
}
Regards
KC
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