I'm trying to generate a hashCode() method for my simple class but i'm not getting anywhere with it. I would appreciate any help. I've implemented the equals() method, which looks as follows, and would also like to know if I need to implement compareTo() method. I've imported java.lang.Character to use character.hashCode() but it doesn't seem to work.
private class Coord{
private char row;
private char col;
public Coord(char x, char y){
row = x;
col = y;
}
public Coord(){};
public char getX(){
return row;
}
public char getY(){
return col;
}
public boolean equals(Object copy){
if(copy == null){
throw new NullPointerException("Object entered is empty");
}
else if(copy.getClass()!=this.getClass()){
throw new IllegalArgumentException("Object entered is not Coord");
}
else{
Coord copy2 = (Coord)copy;
if(copy2.row==this.row && copy2.col==this.col)
return true;
else
return false;
}
}
}
Thanks in advance...
The comparTo() method that is giving me java.lang.Comparable casting error..
public int compareTo(Object copy){
if(copy==null){
throw new NullPointerException("Object entered is empty");
}
else if(copy.getClass()!=this.getClass()){
throw new IllegalArgumentException("Object entered is not Coord");
}
else{
Coord copy2 = (Coord)copy;
if(copy2.row==this.row && copy2.col==this.col){
return 0;
}
else if(copy2.col < this.col){
return -1;
}
else{
return 1;
}
}
}
thanks...
Java Object hashCode() is a native method and returns the integer hash code value of the object.
Simply put, hashCode() returns an integer value, generated by a hashing algorithm. Objects that are equal (according to their equals()) must return the same hash code. Different objects do not need to return different hash codes.
In this program, after getting a list of Method objects of a class object by calling getMethods() method of class object, hashCode() method of Method object is called for each method object of the list. At last, the hashcode is printed along with the method name.
To implement hashCode, you override the default implementation from Object:
@Override
public int hashCode()
{
return row ^ col;
}
This isn't really an ideal hash, since its results are very predictable and it is easy for two different Coord
objects to return the same value. A better hash would make use of the built-in Arrays
class from java.util
(http://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html):
@Override
public int hashCode()
{
return Arrays.hashCode(new Object[]{new Character(row), new Character(col)});
}
You can use this method to generate a pretty good hash with any number of fields.
To implement compareTo, you'll want your class to implement Comparable:
public class Coord implements Comparable<Coord>
Once you've done this, you can make compareTo take an argument of type Coord
rather than type Object
, which will save you the trouble of checking its type.
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