public interface Predicate {
public boolean evaluate(Object obj);
}
class Man {
private int age;
private String name;
private Predicate predicate; //Strategy.
public Man(int a, String n){
this.age = a;
this.name = n;
}
//override equals
public boolean equals(Object obj) {
if(predicate != null)
return predicate.evaluate(obj);
else //Override equals here.
//Do normal comparison }
public static Collection grouped(Collection sourceCollection, Predicate p, Man type) {
predicate = p;
return sourceCollection.retainAll(new ArrayList().add(type));
}
}
public class FindPredicate{
public static void main(String[] args){
ArrayList men = new ArrayList();
for(int i = 0 ;i < 30; i++)
men.add(new Man("Name: " + 1, i);
//From the above collection get all men with age 25
System.out.println(Man.grouped(men, new Predicate() {
public boolean evaluate(Object obj) {
//Compare ages.
if(age == (Man)obj.age) return true;
return false;
}
}, new Man("", 25));
}
}
Roman Rytov wrote:
Assume a collection of objects exists and there is an object
implementing Predicate interface. Also let's say that evaluate(Object
obj) method returns a number of distinct objects (out of this
collection) and the number is noticeably less than total amount of
objects in the collection. Is there a way to get all collections grouped
by the predicator? An example may be schematically written like:
class Man {
String name;
int age;
}
class AgePredicator implements Predicate {
int age;
boolean evaluate (Object obj) {
Man man = (Man)obj;
return man.age == this.age;
}
collection men = { ('Isac', 35), ('Jerry', 32), ('Gonsales', 35),
('Moshe' , 22), ('Hans', 32), ('Mussa', 32)}
afer grouping it's supposed to get 3 collections:
('Isac', 35), ('Gonsales', 35), ('Jerry', 32), ('Hans', 32), ('Mussa', 32)}
('Moshe' , 22),
Do we have something in the API do achieve it easily?
_______________________
Roman Rytov
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