Develop Reference

Problem java Set data replaced/wiped on add

I have actually a problem on a Set in my project (code below)
public static Set<BeanObject> mapToSetBean(Collection<Object> listModel) {
Set<BeanObject> listToReturn = new HashSet<>();
for (Iterator<Object> iterator = listModel.iterator(); iterator.hasNext();) {
Object model = iterator.next();
BeanObject bean = new BeanObject();
bean = mapToBean(model);
listToReturn.add(bean);
}
return listToReturn;
}
When some beans are added to the list they replace another one.
For example:
List{}
add object1 / List{object1}
add object2 / List{object1, object2}
add object1 / List{object1, object2, object3}
add object4 / List{object4, object2, object3}
The equals and the hashcode of the object are override the hashcode are all different and in debug mode we don't enter in the override equals.
When I use an ArrayList everything works but I prefer not to change the type it has a huge impact on my project.
---------------- EDIT ---------------
public static BeanObject mapToBean(Object model) {
BeanObject bean = new BeanObject();
if (model != null) {
bean.setId(model.getId());
if(model.getId() != null){
bean.setIdString(model.getId().toString());
}
if (model.getName() != null) {
bean.setName(model.getName().toLowerCase());
}
bean.setActif(model.getActif());
if (model.getShortName() != null) {
bean.setShortName(model.getShortName().toUpperCase());
}
}
return bean;
}
BeanObject
public class BeanObject implements Comparable<BeanObject> {
/**
* serial
*/
private static final long serialVersionUID = 1L;
private BigInteger id;
private String name;
private String shortName;
private Short actif;
private String idString;
public BeanObject() {
}
public BeanObject(BigInteger id, String libelle) {
this.id = id;
this.name = libelle;
}
/*
* (non-Javadoc)
*
* #see java.lang.Object#equals(java.lang.Object)
*/
#Override
public boolean equals(Object o) {
if (o == null) {
return false;
}
if (!(o instanceof BeanObject)) {
return false;
}
BeanObject other = (BeanObject) o;
boolean result;
if (null == this.id) {
if (null == other.id) {
result = true;
} else {
result = false;
}
} else {
result = this.id.equals(other.id);
}
return result;
}
/*
* (non-Javadoc)
*
* #see java.lang.Object#hashCode()
*/
#Override
public int hashCode() {
return this.id.intValue() * name.hashCode() * shortName.hashCode();
}
public BigInteger getId() {
return id;
}
public void setId(BigInteger id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getShortName() {
return shortName;
}
public void setShortName(String shortName) {
this.shortName = shortName;
}
public Short getActif() {
return actif;
}
public void setActif(Short actif) {
this.actif = actif;
}
public String getIdString() {
return idString;
}
public void setIdString(String idString) {
this.idString = idString;
}
}

Are you certain the BeanObject's hashcode values are unique? That hashcode method seems like it would map a lot of objects to 0 if any of its fields hashed to 0 since it is straight multiplication. I would suggest updating to a more standardized approach for it like the following:
#Override
public int hashCode() {
return Objects.hash(id, name, shortName);
}
Objects.hash is from the java.util package.
If this still doesn't solve the problem, I would double check the hashcode results for each bean object at add time.

Overridden equals and hashCode does not work on custom Object;

I have an below object
class CustomObj{
private String name;
private String dept;
public String getName(){
return this.name;
}
public String getDept(){
return this.dept;
}
private CustomObj(){
}
private CustomObj(CustomObjBuilder builder){
this.name = builder.name;
this.dept= builder.dept;
}
#Override
public boolean equals(Object o) {
if (o == this) return true;
if (o == null || getClass() != o.getClass()) return false;
CustomObj that = (CustomObj) o;
return that.name.equals(name) &&
that.dept.equals(dept);
}
#Override
public int hashCode() {
int result = 31;
result = 31 * result + name.hashCode();
result = 31 * result + dept.hashCode();
return result;
}
public static class CustomObjBuilder{
private String name;
private String dept;
public CustomObjBuilder(String name, String dept){
this.name = name;
this.dept = dept;
}
public CustomObjBuilder setName(String name){
this.name = name;
return this;
}
public CustomObjBuilder setDept(String dept){
this.dept = dept;
return this;
}
public CustomObj build(){
return new CustomObj(this);
}
}
}
and class that uses above
class XYZ{
Set<CustomObj> obj = new HashSet<CustomObj>();
public void process(String a, String b){
CustomObj o = new CustomObj.CustomObjBuilder(a,b).build();
if(!obj.contains(o)){
obj.add(o);
}
}
}
And a test class
class TestXYX{
#Test
public void test(){
XYZ xyz = new XYZ();
xyz.process("TEST","TESTABC");
xyz.process("TEST","TESTABC");
}
}
Beacuse I have overrideen hascode and equals, both the above are equal and when process is called second time, the control should not go into if(!obj.contains(o)) second time and size of the set should be 1. But when i run the test obj.add(o); is called two times. But the values of both this object and that objec inside equals methods are same, but
that.name.equals(name) && that.dept.equals(dept)
inside CustomObj returns false. Can someone please help me understand why?

The code is fine. To verify add an sysout to check Set size:
class XYZ {
Set<CustomObj> obj = new HashSet<CustomObj>();
public void process(String a, String b) {
CustomObj o = new CustomObj.CustomObjBuilder(a, b).build();
if (!obj.contains(o)) { // Fails second time for your use case.
obj.add(o);
}
System.out.println(obj.size()); // This is 1 in your use case.
}
}

How to create own Custom Predicate to compare composite id in hazelcast

I want to create my own custome predicate to compare composite id's inside object. The need is to because i have to write specific date comparison logic on object inside object (composite id). I don't want to compare individual attributes.i want to use composite id because it comes from invoker and I can't get result using Predicate.in and Predicate.equals
My Object structure is like below
Birth{id=BirthId{name='b3', dob=Wed Jan 01 10:53:20 IST 1902}, name='b3', dob=Wed Jan 01 10:53:20 IST 1902, description='MNP'}
and inside IMap it is stored like below
key : BirthId{name='b3', dob=Wed Jan 01 10:53:20 IST 1902}
value : Birth{id=BirthId{name='b3', dob=Wed Jan 01 10:53:20 IST 1902}, name='b3', dob=Wed Jan 01 10:53:20 IST 1902, description='MNP'}
My Java Classes(Birth and Birthid) Structure is below
public class Birth implements Serializable, Portable {
private static final long serialVersionUID = 1L;
private BirthId id;
private String name;
private Date dob;
private String description;
public BirthId getId() {
return id;
}
public void setId(BirthId id) {
this.id = id;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Date getDob() {
return dob;
}
public void setDob(Date dob) {
this.dob = dob;
}
public int hashCode() {
return (new HashCodeBuilder()).append(this.id).append(this.name).append(this.dob).toHashCode();
}
public boolean equals(Object other) {
if (other == this) {
return true;
} else if (!(other instanceof Birth)) {
return false;
} else {
Birth rhs = (Birth) other;
return (new EqualsBuilder()).append(this.id, rhs.id).append(this.name, rhs.name).append(this.dob, rhs.dob).isEquals();
}
}
#Override public String toString() {
return "Birth{" + "id=" + id + ", name='" + name + '\'' + ", dob=" + dob + ", description='" + description + '\'' + '}';
}
public int getFactoryId() {
return 1;
}
public int getClassId() {
return 1;
}
public void writePortable(PortableWriter portableWriter) throws IOException {
portableWriter.writePortable("idComposite", getId());
portableWriter.writeUTF("id", getId().toString());
portableWriter.writeUTF("name", getName());
portableWriter.writeUTF("description", getDescription());
Date date = getDob();
portableWriter.writeLong("dob", ((date == null) ? -1 : date.getTime()));
}
public void readPortable(PortableReader portableReader) throws IOException {
setId((BirthId) portableReader.readPortable("idComposite"));
setName(portableReader.readUTF("name"));
setDescription(portableReader.readUTF("description"));
long date = portableReader.readLong("dob");
setDob(((date == -1) ? null : new Date(date)));
}
}
public class BirthId implements Comparable<BirthId>, Serializable, Portable {
private static final long serialVersionUID = 1L;
private String name;
private Date dob;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Date getDob() {
return dob;
}
public void setDob(Date dob) {
this.dob = dob;
}
public int hashCode() {
return (new HashCodeBuilder()).append(this.name).append(this.dob).toHashCode();
}
public boolean equals(Object other) {
if (other == this) {
return true;
} else if (!(other instanceof BirthId)) {
return false;
} else {
BirthId rhs = (BirthId) other;
return (new EqualsBuilder()).append(this.name, rhs.name).append(this.dob, rhs.dob).isEquals();
}
}
public int compareTo(BirthId rhs) {
return this == rhs ? 0 : (null == rhs ? -1 : (new CompareToBuilder()).append(this.name, rhs.name).append(this.dob, rhs.dob).toComparison());
}
#Override public String toString() {
return "BirthId{" + "name='" + name + '\'' + ", dob=" + dob + '}';
}
public int getFactoryId() {
return 1;
}
public int getClassId() {
return 2;
}
public void writePortable(PortableWriter portableWriter) throws IOException {
portableWriter.writeUTF("name", getName());
Date date = getDob();
portableWriter.writeLong("dob", ((date == null) ? -1 : date.getTime()));
}
public void readPortable(PortableReader portableReader) throws IOException {
setName(portableReader.readUTF("name"));
long date = portableReader.readLong("dob");
setDob(((date == -1) ? null : new Date(date)));
}
public static ClassDefinition getClassDefinition(int portableVersion) {
ClassDefinitionBuilder result = new ClassDefinitionBuilder(1, 2, portableVersion);
result.addUTFField("name");
result.addLongField("dob");
return result.build();
}
}
I have created own custom Predicate to compare dates like below
public class DatePredicate extends AbstractPredicate<Comparable, BirthId> {
Comparable[] values;
private volatile Set<Comparable> convertedInValues;
public DatePredicate() {
}
public DatePredicate(String attribute, Comparable... values) {
if (values == null) {
throw new NullPointerException("Array can't be null");
} else {
this.values = values;
}
}
protected boolean applyForSingleAttributeValue(Map.Entry entry, Comparable attributeValue) {
//My own date comparison logic
return true;
}
public int getId() {
return 99;
}
}
Caller code is
Predicate p = new DatePredicate("id", new BirthId("12345",passSpecifiedDate()));
Result res = imap.values(p);
I am getting below error
Exception in thread "main" com.hazelcast.nio.serialization.HazelcastSerializationException: com.hazelcast.internal.serialization.impl.ArrayDataSerializableFactory#5f007be3 is not be able to create an instance for id: 99 on factoryId: -32
I do not know the best way to create own custom predicate and hazelcast doc does not specify the also.
Could any please guide me how to do this?

#oomph-fortuity, your DatePredicate extends AbstractPredicate which implements IdentifiedDataSerializable and used by built-in Hazelcast predicates. Built-in Predicate Serializable Factory try to deserialize your class & fails since it only knows how to serialize/deserialize built-in Predicates.
Instead, just implement com.hazelcast.query.Predicate interface:
class DatePredicate implements Predicate<BirthId, Birth> {
BirthId birthIdToCompare;
public DatePredicate() {
}
public DatePredicate(BirthId birthId) {
this.birthIdToCompare = birthId;
}
#Override
public boolean apply(Map.Entry<BirthId, Birth> mapEntry) {
BirthId key = mapEntry.getKey();
///your custom logic
return true;
}
}
And call like this
Predicate p = new DatePredicate(new BirthId("12345",passSpecifiedDate()));
Result res = imap.values(p);
Let me know if that works.

Search in ArrayList using Comparator

I had an interview today and I have given two java classes and asked to search dog details by registration number. I know that Java.util.ArrayList.contains(Object) but do not know how to implement when there are more than one fields.
The second question was: what is the most efficient search techniques you can use in this example? I thought about Collections.binarySearch but not sure that it is the most efficient in this example. If so, how can I implement it?
DogSort.java
public class DogSort {
public static void main(String[] args) {
ArrayList<Dog> listDog = new ArrayList<Dog>();
Scanner sc = new Scanner(System.in);
listDog.add(new Dog("Max", "German Shepherd", "33"));
listDog.add(new Dog("Gracie","Rottweiler","11"));
Collections.sort(listDog, Dog.COMPARE_BY_NAME);
System.out.println(listDog);
}
}
Dog.java
class Dog {
private String name;
private String breed;
private String registrationNumber;
public Dog(String name, String breed, String registrationNumber) {
this.name = name;
this.breed = breed;
this.registrationNumber = registrationNumber;
}
public static Comparator<Dog> COMPARE_BY_NAME = new Comparator<Dog>() {
public int compare(Dog one, Dog other) {
return one.name.compareTo(other.name);
}
};
//getter and setter methods for all private variable
}

I agree with #Pritam Banerjee's answer. The most efficient search technique is to use HashMap in this scenario. I would recommend to use HashSet but the HashSet#contains method returns boolean, so just use map. Here is the code snippet.
Just for Information When using hash based collection/map dont forget to implement hashCode and equals method properly.
public class DogSearch {
public static void main(String[] args) {
Map<String, Dog> dogs = new HashMap<String, Dog>();
Dog max = new Dog("Max", "German Shepherd", "1001");
Dog gracie = new Dog("Gracie", "Rottweiler", "1002");
Dog luca = new Dog("Luca", "Labrador", "1003");
Dog tiger = new Dog("Tiger", "Beagle", "1004");
Dog meemo = new Dog("Meemo", "Bulldog", "1005");
Dog lacie = new Dog("Lacie", "German Shorthaired Pointer", "1006");
dogs.put(max.getRegistrationNumber(), max);
dogs.put(gracie.getRegistrationNumber(), gracie);
dogs.put(luca.getRegistrationNumber(), luca);
dogs.put(tiger.getRegistrationNumber(), tiger);
dogs.put(meemo.getRegistrationNumber(), meemo);
dogs.put(lacie.getRegistrationNumber(), lacie);
Dog result = dogs.get("1002");
if (result == null) {
System.out.println("Dog not found");
} else {
System.out.println(result);
}
}
}
class Dog {
private String name;
private String breed;
private String registrationNumber;
public Dog(String name, String breed, String registrationNumber) {
this.name = name;
this.breed = breed;
this.registrationNumber = registrationNumber;
}
public static Comparator<Dog> COMPARE_BY_NAME = new Comparator<Dog>() {
public int compare(Dog one, Dog other) {
return one.name.compareTo(other.name);
}
};
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getBreed() {
return breed;
}
public void setBreed(String breed) {
this.breed = breed;
}
public String getRegistrationNumber() {
return registrationNumber;
}
public void setRegistrationNumber(String registrationNumber) {
this.registrationNumber = registrationNumber;
}
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((breed == null) ? 0 : breed.hashCode());
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result + ((registrationNumber == null) ? 0 : registrationNumber.hashCode());
return result;
}
#Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Dog other = (Dog) obj;
if (breed == null) {
if (other.breed != null)
return false;
} else if (!breed.equals(other.breed))
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
if (registrationNumber == null) {
if (other.registrationNumber != null)
return false;
} else if (!registrationNumber.equals(other.registrationNumber))
return false;
return true;
}
#Override
public String toString() {
return "Dog [name=" + name + ", breed=" + breed + ", registrationNumber=" + registrationNumber + "]";
}
}
Time Complexity
Insertion : O(1)
Search : O(1)

Add it to a HashMap with Registration as Key and Dog object as the value and then search the Map.
O(1) insertion and O(1) searching.
Binary Search O(log n).

For the first question ie to search details by registration number here is the code
import java.util.Comparator;
import java.util.TreeMap;
public class DogSort {
public static void main(String[] args) {
TreeMap<Integer, Dog> listDogs = new TreeMap<>();
listDogs.put(33, new Dog("Max", "German Shepherd", "33"));
listDogs.put(11, new Dog("Gracie", "Rottweiler", "11"));
System.out.println(listDogs);
System.out.println(listDogs.containsKey(11));
System.out.println(listDogs.get(11));
}
}
class Dog {
private String name;
private String breed;
private String registrationNumber;
public Dog(String name, String breed, String registrationNumber) {
this.name = name;
this.breed = breed;
this.registrationNumber = registrationNumber;
}
public static Comparator<Dog> COMPARE_BY_NAME = new Comparator<Dog>() {
public int compare(Dog one, Dog other) {
return one.name.compareTo(other.name);
}
};
#Override
public String toString() {
return "Dog [name=" + name + ", breed=" + breed + ", registrationNumber=" + registrationNumber + "]";
}
}
It is very difficult to get the details of dog by registration number using arraylist, but with map it is quite easy.
And you can override the hashcode and equals method like this but the arraylist compare method works differently.
What you can do is you can write a method which can search details by registration number. The method will have to iterate the list and find the Dog object,and if the list is sorted then you need to implement your own binary search to get the Dog object according to the registration number.
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class DogSort {
public static void main(String[] args) {
ArrayList<Dog> listDog = new ArrayList<Dog>();
listDog.add(new Dog("Max", "German Shepherd", "33"));
listDog.add(new Dog("Gracie", "Rottweiler", "11"));
Collections.sort(listDog, Dog.COMPARE_BY_NAME);
System.out.println(listDog);
System.out.println(listDog.contains(new Dog("Max", "Rottweiler", "33")));
}
}
class Dog {
private String name;
private String breed;
private String registrationNumber;
public Dog(String name, String breed, String registrationNumber) {
this.name = name;
this.breed = breed;
this.registrationNumber = registrationNumber;
}
public static Comparator<Dog> COMPARE_BY_NAME = new Comparator<Dog>() {
public int compare(Dog one, Dog other) {
return one.name.compareTo(other.name);
}
};
#Override
public String toString() {
return "Dog [name=" + name + "]";
}
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((registrationNumber == null) ? 0 : registrationNumber.hashCode());
return result;
}
#Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Dog other = (Dog) obj;
if (registrationNumber == null) {
if (other.registrationNumber != null)
return false;
} else if (!registrationNumber.equals(other.registrationNumber))
return false;
return true;
}
}

cqengine cant index by equals

I'm trying to add an index where my override equals() determines if two objects are the same or not.
Car.java
public static class Car {
final String id;
private String name;
public Car(String id, String name) {
this.id = id;
this.name = name;
}
public String getId() {
return id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public static final Attribute<Car, Car> CAR = new SimpleAttribute<Car, Car>() {
#Override
public Car getValue(Car car, QueryOptions queryOptions) {
return car;
}
};
#Override
public String toString() {
return "Car{" + "id=" + id + ", name=" + name + '}';
}
}
Fetcher.java
public static final ResultSet<Car> get(final IndexedCollection<Car> indexedCollection, final Car car) {
return indexedCollection.retrieve(QueryFactory.equal(Car.CAR, car));
}
Main.java
public static void main(String args[]) {
IndexedCollection<Car> cars = new ConcurrentIndexedCollection<>();
cars.addIndex(NavigableIndex.onAttribute(Car.CAR));
}
The problem is on this line cars.addIndex(NavigableIndex.onAttribute(Car.CAR)); where the error message is no suitable method found for onAttribute(Attribute<Car,Car>). Am I doing something wrong here or is there another call I should be using instead?

Remove cars.addIndex(NavigableIndex.onAttribute(Car.CAR));, because it is not really an usefull index... and I think this was not a motivation of the developer. You should create Attributes for CAR_ID and CAR_NAME and create an Query for comparison. In this case I misuse (to achieve what you expect) IndexedCollection as a simple Set. But... here is a possible solution, if I have understood you correctly:
Override equals in Car:
class Car {
private final int id;
private String name;
public Car(int i, String name) {
this.id = i;
this.name = name;
}
public int getId() {
return id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
#Override
public boolean equals(Object obj) {
if(this == obj) return true;
if(obj == null) return false;
if (!(obj instanceof Car)) return false;
Car car = (Car) obj;
if(car.getId() == this.getId())
if(car.getName().equals(this.getName()))
return true;
return false;
}
public static final Attribute<Car, Car> CAR = new SimpleAttribute<Car, Car>() {
#Override
public Car getValue(Car car, QueryOptions queryOptions) {
return car;
}
};
#Override
public String toString() {
return "Car{" + "id=" + id + ", name=" + name + '}';
}
}
Main:
IndexedCollection<Car> cars = new ConcurrentIndexedCollection<>();
cars.add(new Car(1, "test"));
cars.add(new Car(2, "test2"));
cars.add(new Car(3, "test3"));
Car s = new Car(2, "test2");
ResultSet<Car> cs= cars.retrieve(QueryFactory.equal(Car.CAR, s));
cs.forEach(c -> System.out.println(c.toString()));