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.
}
}
Related
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.
So i have 2 classes, and in the class race i have a method ( public Athlete getAthlete(int codAthlete) ) that
should return the object corresponding to the Athlete with the code passed by parameter, but i am not sure how to
implement it. Can someone give me a hand?
public class Athlete {
private int codAthlete;
private String name;
public Athlete(int codAthlete){
this.codAthlete = codAthlete;
}
public int getCodAthlete() {
return this.codAthlete;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return this.name;
}
public String getInformation() {
return "Code: " + this.codAthlete +
" Name " + this.name;
}
}
.
public class Race {
private String idRace;
private Set<Athlete> athletes;
public Race(String idRace) {
athletes = new HashSet<>();
this.idRace = idRace;
}
public String getIdRace () {
return this.idRace;
}
public Athlete getAthlete(int codAthlete){
for(Athlete a: Athlete){
if(a.getCodAthlete() == codAthlete)
a.getInformation();
}
return (????);
// Returns the object corresponding to the Athlete with the code passed by parameter.
}
}
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()));
I am using a custom class object as the key for a HashMap. In this class definition, I have overridden the equals() and hashCode() methods.
public class TimeTableDataModel {
Map <Course, List <Timings>> tm;
TimeTableDataModel() {
tm = new HashMap<>();
}
void addCourseItem(Course course) {
tm.put(course, new ArrayList<Timings>());
}
void addNewTimeTableItem(Course course, Timings newTiming) {
List <Timings> t;
if(!tm.containsKey(course)) {
addCourseItem(course);
}
t = tm.get(course);
t.add(newTiming);
tm.put(course, t);
}
public static final class Course {
private final String courseCode;
private final String courseName;
private final String section;
private final String group;
Course(String code, String courseName, String section, String group) {
this.courseCode = code;
this.courseName = courseName;
this.section = section;
this.group = group;
}
public String getCourseCode() { return courseCode; }
public String getCourseName() { return courseName; }
public String getSection() { return section; }
public String getGroup() { return group; }
#Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof Course)) {
return false;
}
Course otherObj = (Course) obj;
return Objects.equals(courseCode,otherObj.courseCode)
&& Objects.equals(courseName, otherObj.courseName)
&& Objects.equals(section, otherObj.section)
&& Objects.equals(group, otherObj.group);
}
#Override
public int hashCode() {
return Objects.hash(courseCode, courseName, section, group);
}
}
public static class Timings {
String time;
String day;
String room;
Timings(String time, String day) {
setTime(time);
setDay(day);
}
public String getTime() { return time; }
public String getday() { return day; }
public void setTime(String time) { this.time = time; }
public void setDay(String day){this.day = day;}
}
}
In above code I have created Course class to be used as the key for the HashMap and using a List<Timings> for values. What I intend is to get a List of timings when a Course is passed to hm.get(course). So far I can get a keyset then sequentially get values for each course.
for(Course c : timetable.tm.keySet()) {
System.out.println(c.getCourseCode() + " " + c.getCourseName());
for(Timings t : timetable.tm.get(c)) {
System.out.println(t.time + " " +t.room + " "+ t.day);
}
};
Here's the code that populates the HashMap
static TimeTableDataModel timetable = new TimeTableDataModel();
Course course = new Course(courseCode,null,section,group);
Timings dt = new Timings(time, getDayOfWeek(i));
dt.room = roomNo;
timetable.addNewTimeTableItem(course, dt);
So to get the timings for a particular course I have to traverse the whole HashMap until the desired course Key is found. What I want is a way to distinguish between each course object contained in the HashMap Key, so I can get Timings for any random course without traversing the whole KeySet.
Thanks in advance. Please ask if somethings is unclear in code
Problem what I see here is
if(!tm.containsKey(course)){
addCourseItem(course);
}
and
if (this == obj) {
return true;
}
because you are comparing the object. Since both are same class objects equals will always return true and map concludes it as duplicate key.
How to check following object is blank or not? I have below class and how could I check that my sample class has nothing data without checking every member of it?
public class Test {
public static void main(String[] args){
Sample sample = new Sample();
if(sample!=null){
System.out.println("Object is blank..");
}
}
}
class Sample {
private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
First you need to define what "blank" means in business terms. What exactly is a "blank" object? Is it an object with a null name? With an empty string name? With some other combination of empty parameters?
Once you've defined what a "blank" object actually is, I recommend adding a method to perform that logic based on the object's current contents and return the results:
public boolean isBlank () {
return ...; // whatever "blank" means
}
If possible I advise against using a flag-based approach. While there are certainly valid reasons for it, adding a flag means your setters must maintain the correct value of the flag at all times (and you must also update it after deserialization).
I am assuming that by emptiness of object, you mean that the instance variables are not initialized. I don't think there is any available method to check such emptiness of an object.
If you have to do this, then you may need to write your own method checking the fileds. You should check for the default values of the primitives and null check for object types. An example of such a method for your class is:
public boolean isEmpty() {
if(this.id == 0 && this.name == null)
return true;
else
return false;
}
Please don't consider this as the perfect implementation, so customize as per your need.
One option to create a boolean flag and manipulate it in setters.
Make a private isBlank:
private boolean isBlank=true;
then have setters call isBlank=false. Any setter calls will make the object not blank. Then add a getter checkIsBlank( that returns isBlank.
Note that the setters should detect a set to null. In that case, they'll need to check all fields. This is left as an exercise to the reader.
What I would do, provide a constructor that takes id and name, therefore you know the object will never be blank:
public class Sample{
private int id;
private String name;
public Sample(int id, String name){
this.id = id;
this.name = name;
}
}
A hack that you could do with your current class is override the toString method:
class Sample {
private int id;
private String name;
#Override
public String toString(){
try{
return Integer.toString(id) + name;
} catch(Execption e){
return "";
}
}
}
if(sample.toString().isEmpty())
System.out.println("Object is blank");
You could check if the object is blank by either comparing it to a newly-instantiated object.
public boolean isBlank() {
return this.equals(new Sample());
}
#Override
public boolean equals(Object o) {
boolean toRet;
if(o == null || !o instanceof Sample) {
toRet = false;
}
else {
Sample b = (Sample) o;
toRet = this.id == b.id
&& (this.name == null ? b.name == null : this.name.equals(b.name));
}
return toRet;
}
Old answer: What you can do is create a modified boolean, which is initialized as false, then set to true any time a setter is called.
class Sample {
public static final int INVALID_ID = -1;
private int id = Sample.INVALID_ID;
private String name = null;
private boolean modified = false;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
modified = true;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
modified = true;
}
public boolean isModified() {
return modified;
}
}