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Abstract Class Java

I need to write abstract class, which looks like this.
public abstract class Value {
public abstract String toString();
public abstract Value add(Value v);
public abstract Value sub(Value v);
public abstract boolean eq(Value v);
public abstract boolean lte(Value v);
public abstract boolean gte(Value v);
public abstract boolean neq(Value v);
public abstract boolean equals(Object other);
public abstract int hashCode();
public abstract Value create(String s);
}
Now I need to make few classe, which inherit from that one. I started from Int class and implemented it like this:
public class Int extends Value {
int val;
public String toString() {
String toStr = Integer.toString(val);
return toStr;
}
public Int add(Value v) {
Int result = new Int();
if(v instanceof Int) {
Int temp = (Int) v;
result.val = val + temp.val;
}
return result;
}
public Int sub(Value v) {
Int result = new Int();
if(v instanceof Int) {
Int temp = (Int) v;
result.val = val - temp.val;
}
return result;
}
public boolean eq(Value o) {
if(this == o) return true;
if(this == null) return false;
if(getClass() != o.getClass()) return false;
Int other = (Int) o;
return toString() == other.toString();
}
public boolean lte(Value v) {
if(v instanceof Int) {
Int temp = (Int) v;
return this.val < temp.val;
}
return false;
}
public boolean gte(Value v) {
if(v instanceof Int) {
Int temp = (Int) v;
return this.val > temp.val;
}
return false;
}
public boolean neq(Value v) {
if(v instanceof Int) {
Int temp = (Int) v;
return !eq(temp);
}
return true;
}
public boolean equals(Object o) {
if(this == o) return true;
if(this == null) return false;
if(getClass() != o.getClass()) return false;
Int other = (Int) o;
return toString() == other.toString();
}
public int hashCode() {
Integer hash = val;
return hash.hashCode();
}
public Int create(String s) {
val = Integer.parseInt(s);
return this;
}
}
Everything is compiling and working, but I have no clue if my hashcode() function and equals() are good. Furthermore i want to use create() to make objects like this:
getInstance().create("1234");
Is my method also sufficient?

Everything is compiling and working, but I have no clue if my hashcode() function and equals() are good.
Your equals() should compare int val and not result of toString() of compared objects (this.val == other.val).
Your hashCode() looks good, though I would add #Override to it (same with equals()).
Furthermore i want to use create() to make objects like this: getInstance().create("1234");
Looking at its implementation, it looks fine (i.e. would work according to your needs):
public Int create(String s) {
val = Integer.parseInt(s);
return this;
}
though I don't think you really want to use it with getInstance(). Simply Int.create() would be enough:
public static Int create(String s) {
val = Integer.parseInt(s);
return new Int(val);
}
Note that you would need a private constructor.
Also, as someone noted in the comments, consider using generics instead of inheritance.

The hashCode() method is fine (although I'd add an #Override annotation, just to make the code easier to maintain and avoid mistakes), but the equals(Object) definitely isn't.
Following the logic you have in place, == isn't the right way to compare strings. You should use equals instead (see, e.g., How do I compare strings in Java?). In addition, as Joakim Danielson noted in the comments, this can never be null - you should check if o is null instead:
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null) {
return false;
}
if(getClass() != o.getClass()) {
return false;
}
Int other = (Int) o;
return toString().equals(other.toString()); // Here!
}
But in all fairness, there's no reason to use toString - you could just compare the internal val:
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null) {
return false;
}
if(getClass() != o.getClass()) {
return false;
}
Int other = (Int) o;
return val == other.val; // Here!
}

First when you override Methods please do it with #Override Annotation. Then i would implement your equals method in another way. Just do return this.val == other.val instead of doing this.toString() == other.toString(). Your toString() method implementation is ok. Your hashCode is good as well. But please remove that create method. Use a constructor instead.

Can I implement equals() method using eq() like this ?
public boolean equals(Object o) {
Value compare = (Value) o;
return eq(compare);
}

How to make custom Tuple class generic?

I'm trying to make a generic tuple class. It stores its elements as an ArrayList. Of course, this class should override hashcode and equals methods.
How could I make hashcode method for this class? You see, in the code, I am having trouble.
Also, for the equals method, why does the compiler force me to use the '?'. Why couldn't I just use the T?
public static class Tuple<T> {
ArrayList<T> tuple = new ArrayList<>();
public Tuple(ArrayList<T> items) {
for (T item : items) {
tuple.add(item);
}
}
#Override
public int hashCode() {
T sum = ???;
for (T item : tuple) {
sum += item.hashCode();
}
return sum;
}
#Override
public boolean equals(Object o) {
if (o instanceof Tuple<?>) {
Tuple<?> tup= (Tuple<?>) o;
if (tup.tuple.size() != this.tuple.size()) {
return false;
}
for (int i = 0; i < this.tuple.size(); i++) {
if (this.tuple.get(i) != tup.tuple.get(i)) {
return false;
}
}
return true;
} else {
return false;
}
}
}

As mentioned in the comments, we should delegate the hashCode and the equals methods to the ArrayList<T> tuple instance variable. For the hashCode it's trivial. For the equals it's just a little more complicated than that because we don't want our custom Tuple to be equals with an ArrayList. So here it is:
public class Tuple<T> {
// I made this private because I'm pedantric ;)
private final ArrayList<T> tuple = new ArrayList<>();
// this does the same as your code, it's just easier to read
public Tuple(ArrayList<T> items) {
tuple.addAll(items);
}
#Override
public int hashCode() {
return tuple.hashCode();
}
// generated by eclipse
#Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Tuple other = (Tuple) obj;
if (tuple == null) {
if (other.tuple != null)
return false;
} else if (!tuple.equals(other.tuple))
return false;
return true;
}
}
If you want to deal with the case when the tuple can be null, then you can use a slightly more complex hashCode:
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((tuple == null) ? 0 : tuple.hashCode());
return tuple.hashCode();
}
In general, I don't like to write these methods myself. Usually, I make my IDE to generate the stuff. All I need to take care of is to re-generate it when I add new fields. Apache HashCodeBuilder and EqualsBuilder are also great alternatives.

Equals method does not return true for same object

#IdClass=(value = TripleKey.class)
class Triple {
String subject;
String predicate;
String object;
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
if (!super.equals(o)) return false;
Triple triple = (Triple) o;
if (!subject.equals(triple.subject)) return false;
return predicate.equals(triple.predicate);
}
#Override
public int hashCode() {
int result = super.hashCode();
result = 31 * result + subject.hashCode();
result = 31 * result + predicate.hashCode();
return result;
}
}
my objects are:
{
"subject": "http://www.someurl.com/thing/resources/<owner>#SenMLJSON",
"predicate": "probes_in",
"object":"http://sweet.jpl.nasa.gov/2.3/matrSediment.owl#clay"
}
and
{
"subject": "http://www.someurl.com/thing/resources/<owner>#SenMLJSON",
"predicate": "probes_in",
"object":"http://sweet.jpl.nasa.gov/2.3/matrSediment.owl#sand"
}
When I try the following I still have duplicates :
public static List<Triple> mergeTripleLists(List<Triple> oldList, List<Triple> newList) {
Set<Triple> tripleSet = new HashSet<>(oldList);
tripleSet.removeAll(newList);
tripleSet.addAll(newList);
return new ArrayList<>(tripleSet);
}

The problem is in:
if (!super.equals(o)) return false;
If should work after removing it.

The problem is the call to the equals method of the super class which uses object reference to test equality, so remove the line with
!super.equals(o)
You also need to remove the call to the hashCode method of the super class.

how to subtract ArrayList using removeall() in java?

I have array list in java:
List<Correction> Auv=new ArrayList<>();
List<Correction> Produv=new ArrayList<>();
then I want to substract Produv value by Auv, here's an example:
Produv.add(new Correction("a","b"));
Produv.add(new Correction("a","c"));
Produv.add(new Correction("b","d"));
Produv.add(new Correction("b","c"));
Auv.add(new Correction("c","a"));
Auv.add(new Correction("b","c"));
Produv.removeall(Auv);
but nothing subtracted, the array still contain it initial value, is there any way to do this?
I try to override equals(), and still got the same result
here the code of my Correction class:
public class Correction {
private String node0;
private String node1;
public Correction(String node0, String node1) {
this.node0 = node0;
this.node1 = node1;
}
public void setNode0(String node0){
this.node0=node0;
}
public void setNode1(String node1){
this.node1=node1;
}
public String getNode0(){
return node0;
}
public String getNode1(){
return node1;
}
#Override
public boolean equals(Object object){
boolean same = false;
if (object != null && object instanceof Correction)
{
same = this.node0 == ((Correction) object).node1 && this.node1 == ((Correction) object).node1;
}
return same;
}
}
Solved!!
it just simply a mistake on overriding equals() method(thank's guys)
here my correction:
#Override
public boolean equals(Object object){
boolean same = false;
if (object != null && object instanceof Correction)
{
same = (this.node0 == ((Correction) object).node1 && this.node1 == ((Correction) object).node0)||(this.node0 == ((Correction) object).node0 && this.node1 == ((Correction) object).node1);
}
return same;
}

Your equals method looks wrong. It makes more sense to compare this.node0 to ((Correction) object).node0.
I think it should be:
public boolean equals(Object object){
boolean same = false;
if (object != null && object instanceof Correction)
{
same = this.node0.equals(((Correction) object).node0) && this.node1.equals(((Correction) object).node1);
}
return same;
}
Also, is this a typo?
Auv.add("c","a");
Auv.add("b","c");
It should probably be :
Auv.add(new Correction ("c","a"));
Auv.add(new Correction ("b","c"));

How to remove duplicates in the Java HashSet

I have a set of this structure. How to remove duplicates of equal object of that class? Equals means field File plik is the same.
EDIT:
But the problem gut bigger I don't have duplicates but I would like to replace old SET member by new.
Withoud 3rd party libraries.
import java.io.*;
public class WordInfo implements Serializable {
File plik;
Integer wystapienia;
public WordInfo(File plik, Integer wystapienia) {
this.plik = plik;
this.wystapienia = wystapienia;
}
public String toString() {
// if (plik.getAbsolutePath().contains("src") && wystapienia != 0)
return plik.getAbsolutePath() + "\tWYSTAPIEN " + wystapienia;
// return "";
}
}
EDIT
I don't have this HashCodeBuilder I want to use Java standard libraries
public int hashCode() {
return new HashCodeBuilder(17, 31).append(plik).append(wystapienia).toHashCode();
}
public boolean equals(Object obj) {
File f = (File) obj;
return(plik.getAbsoluteFile().equals(f.getAbsolutePath()));
}

As discussed here, override equals.
public class Person {
private String name;
private int age;
// ...
public int hashCode() {
return new HashCodeBuilder(17, 31). // two randomly chosen prime numbers
// if deriving: appendSuper(super.hashCode()).
append(name).
append(age).
toHashCode();
}
public boolean equals(Object obj) {
if (obj == null)
return false;
if (obj == this)
return true;
if (obj.getClass() != getClass())
return false;
Person rhs = (Person) obj;
return new EqualsBuilder().
// if deriving: appendSuper(super.equals(obj)).
append(name, rhs.name).
append(age, rhs.age).
isEquals();
}
}

public class WordInfo implements Serializable {
File plik;
Considering that following is how you can override the equals and hashCode method as per your requirement:
#Override
public boolean equals(Object obj) {
if(this == obj) return true;
if(!(obj instanceof WordInfo)) return false;
return this.plik.equals(((WordInfo) obj).plik);
}
#Override
public int hashCode() {
return this.plik.hashCode();
}