Some basics for java

java_2_exam

Some Arrays and stuff to use with them....

private String[] receivers; // definition...
this.receivers = targets.clone() // not just this.recievers = recievers !! unsafe

for each is kinda usefull here...
for (int i: recievers) {
  System.out.println(recievers[i].name);
}

Equals with hashcode for integer values (integer is primitive therefore no hasCode() for it)

public boolean equals(Object obj) {
  if (!(obj instanceof Point)) return false;
  Point point = (Point) obj;
  return (this.x == point.x) && (this.y == point.y) && (this.name.equals(point.name));
}
    
public int hashCode() {
  int hash = 1;    // universal --> hash = hash + hash * prime + attr
  hash += hash * 31 +x;
  hash += hash * 31 +y;
  hash += hash * 31 + name.hashCode();
  return hash;
}

Here is the eqauls with hashcode for objects (list has a function hashCode())

public boolean equals(Object object) {
  if (!(object instanceof ListPolygon)) return false;
  return vertices.equals(((ListPolygon)object).vertices);
}
    
public int hashCode() {
  return vertices.hashCode();
}

Exceptions

classes - inheriting from Exception

   public MessengerException() {
       super();
   }
   public MessengerException(String msg) {
       super(msg);
   }
   public MessengerException(Throwable cause) {
       super(cause);
   }
   public MessengerException(String msg, Throwable cause) {
        super(msg, cause);
   }

Collections

List - ArrayList
     \ HashList
Set - HashSet
    \ TreeSet
Map - HashMap

private List<Country> countries = new ArrayList<Country>(); // definition


safely return collection so they cannot mess with it

return Collections.unmodifiableList(countries);

sure can use iterator with those collections

for (Iterator it = countries.iterator(); it.hasNext(); ) {
Country c = (Country) it.next();
result += c.getPopulation();
}

additionally maybe these imports can be useful also for those collections...

import java.util.List;
import java.util.ArrayList;
import java.util.Collection; // is the implementation of the below intefrace
import java.util.Collections;
import java.util.Iterator;

and with those exceptions:

try and catch block is used to catch and throw them the right way....

try {
} catch(NoRouteToHostException e) {
throw new TargetUnreachableException("not reachable", e);
}

and dont forget that everytime in function one gets thrown like :
throw new TargetUnreachableException("not reachable", e);
it has to be mentioned in header of the function like extends, but :
throws TargetUnreachableException

simple as that

see this one for more :P https://gist.github.com/1584289