Develop Reference

Simplify Overridden equals and hashcode methods

I have a person class with overridden hashcode and equals, looks something like this :
class PersonKey {
private String personUID;
private String ssnUID;
private String countryCode;
public PersonKey (
String personUID, String ssnUID, String countryCode) {
this.personUID= personUID;
this.ssnUID= countryCode;
this.countryCode= countryCode;
}
.....
}
This class already had personUID and ssnUID fields and I am introducing countryCode as a new field.
This class already had a complicated hashcode and equals method, with the inclusion of countryCode the logic got even more complicated. Is there a way I can reduce the Cyclomatic Complexity using inheritance or wrapper class?
HashCode :
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + getOuterType().hashCode();
result = prime * result;
if (personUID != null) result += personUID.hashCode();
else result += ((ssnUID == null) ? 0 : ssnUID.hashCode());
if ((personUID != null || ssnUID != null)
&& (countryCode != null)) {
result += countryCode.hashCode();
}
return result;
}
Equals :
#Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
PersonKey other = (PersonKey) obj;
if (!getOuterType().equals(other.getOuterType())) {
return false;
}
// For the purposes of mapping any "empty" Person (null
// personUID and ssnUID) is considered to be unique so return
// false
if ((ssnUID == null) && (personUID == null)) {
return false;
}
// Only evaluate ssnUID if the personUID is null
if (personUID == null) {
// If the current ssnUID matches the personUID
// from the other key the keys will be assumed to match
if (ssnUID.equals(other.personUID)) {
if (StringUtils.isBlank(countryCode) && StringUtils.isBlank(other.countryCode)) {
return true;
} else {
if (countryCode.equals(other.contryCode)) return true;
}
} else if (other.personUID != null) {
return false;
}
if (ssnUID.equals(other.ssnUID)) {
if (StringUtils.isBlank(v) && StringUtils.isBlank(other.countryCode)) {
return true;
} else {
if (countryCode.equals(other.countryCode)) return true;
}
}
}
// If the current personUID matches the personUID
// the keys will
// be considered a match regardless of the value of the ssnUID.
else if (personUID .equals(other.personUID)) {
if (StringUtils.isBlank(contryCode) && StringUtils.isBlank(other.contryCode)) {
return true;
} else {
if (countryCode.equals(other.countryCode)) return true;
}
}
// If the current personUID matches the ssnUID
// from the other key, and the other keys personUID is null
// the keys will be considered a match
else if ((other.personUID == null)
&& (personUID.equals(other.ssnUID))) {
if (StringUtils.isBlank(contryCode) && StringUtils.isBlank(other.contryCode)) {
return true;
} else {
if (countryCode.equals(other.countryCode)) return true;
}
}
return false;
}

You can use Lombok's #EqualsAndHashCode would be the fastest option.
Example and documentation can be found here: https://projectlombok.org/features/EqualsAndHashCode
If you create a new method in your class:
#EqualsAndHashCode(onlyExplicitlyIncluded = true)
class PersonKey {
private String personUID;
private String ssnUID;
private String countryCode;
...
#EqualsAndHashCode.Include
public String uidOrSsn() {
return personUID != null ? personUID : ssnUID;
}
}
This way you're telling Lombok to only create the equals and hashCode for the uidOrSsn() method declared. Whichever the non-null value of personUID or ssnUID, then it will be generated.

Check ArrayList for duplicates

Class:
public class Variant
{
private String variant;
private String quantity;
//getters and setters
}
ArrayList:
ArrayList<Variant> variantList = getVariantsList();
Now I want to check whether variantList contains a duplicate entry of variant or not? Please note that variant having two entries with different quantity are to be considered as duplicates.

You can simply ovveride your equals method in your Variant class and provide all the rules for equality in that method.
#Override
public boolean equals(Object obj) {
..
Then you can use contains method or just pass it to a Set, that eliminates all your duplicates.
If you want variant having two entries with different quantity also considered as dup, then you can add that condition in your equals.

Override equals(Object obj) method and try to compare the object on variant and quantity.
Try to loop thru the variantList and do check for duplicity using variantList.contains(variant).

There are two things you need to do:
Override the equals() in your Variant class(minimal code below):
Please note that the below code only checks for quantity and not the variant prop. Your IDE might help you to generate the equals() as well.
#Override
public boolean equals(Object object) {
boolean isEqual = (this == object);
if(object instanceof Variant){
Variant variant = (Variant) object;
isEqual = this.quantity.equals(variant.quantity);
}else{
isEqual = false;
}
return isEqual;
}
Check if the List contains the object - which will use the equals() to check if both are equal.
for (Variant variant : variantList) {
if (variantList.contains(variant)) {
//do logic if its present
}
}

Just check one object with other objects of list
Override equals method in Variant class
#Override
public boolean equals(Object obj) {
if (obj != null) {
if (obj instanceof Variant) {
Variant temp = (Variant) obj;
return this.quantity.equals(temp.quantity); //for different quantity
} else {
return false;
}
}
return false;
}
Then check :
for (int i = 0; i < variantList.size(); i++) {
for (int j = 0; j < variantList.size(); j++) {
if (i != j) {
if (iList.get(i).equals(iList.get(j))) {
//logic when duplicate
break;
}
}
}
}

Follow the below guidelines:
Your Class Variant must override the equals method, since you define a duplicate condition based on quality hence in the equals method check for quality attribute value i.e.
public class Variant {
private String variant;
private String quantity;
public Variant(String variant, String quantity) {
this.variant = variant;
this.quantity = quantity;
}
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result
+ ((quantity == null) ? 0 : quantity.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;
Variant other = (Variant) obj;
if (quantity == null) {
if (other.quantity != null)
return false;
} else if (!quantity.equals(other.quantity))
return false;
return true;
}
}
Create a method which basically checking whether your list contains the duplicate entries(Variant) or not and return true and false accordingly:
private static boolean isListContainsDuplicateEntries(
ArrayList variantList) {
final List setToReturn = new ArrayList();
for (Variant v : variantList) {
if (!setToReturn.contains(v)) {
setToReturn.add(v);
} else {
return true;
}
}
return false;
}
Now, test the functionality:
public static void main(String[] args) {
Variant variant1 = new Variant("1", "100");
Variant variant2 = new Variant("2", "200");
Variant variant3 = new Variant("3", "200");
ArrayList<Variant> variantList = new ArrayList<>();
variantList.add(variant1);
variantList.add(variant2);
variantList.add(variant3);
System.out.println(Variant.isListContainsDuplicateEntries(variantList));
Output: true

You can use contains():
if (variantList.contains(**<some other Variant object>**)){
...
}

You can simply override your equals method in your Variant and try like this
List<Varient> list =getVariantsList();
System.out.println("here list size"+list.size());
Set<Varient> set = new HashSet<Varient>(list);
System.out.println("here"+set.size());

Create a varient Object:
public class Varient {
private String variant;
private String quantity;
public String getVariant() {
return variant;
}
public void setVariant(String variant) {
this.variant = variant;
}
public String getQuantity() {
return quantity;
}
public void setQuantity(String quantity) {
this.quantity = quantity;
}
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof Varient)) return false;
Varient varient = (Varient) o;
if (!quantity.equals(varient.quantity)) return false;
if (!variant.equals(varient.variant)) return false;
return true;
}
#Override
public int hashCode() {
int result = variant.hashCode();
result = 31 * result + quantity.hashCode();
return result;
}
}
Here is your main Program;
public class Test {
public static void main (String [] args){
// getVariantsList() here your list
List<Varient> list =getVariantsList();
Set<Varient> set = new LinkedHashSet<Varient>(list);
}
}

public class Variant {
private String variant;
private String quantity;
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((variant == null) ? 0 : variant.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;
Variant other = (Variant) obj;
if (variant == null) {
if (other.variant != null)
return false;
} else if (!variant.equals(other.variant))
return false;
return true;
}
public String getVariant() {
return variant;
}
public void setVariant(String variant) {
this.variant = variant;
}
public String getQuantity() {
return quantity;
}
public void setQuantity(String quantity) {
this.quantity = quantity;
}
public static void main(String[] args) {
// HashSet<Variant> set = new HashSet<>();
// LinkedHashSet<Variant> linkedSet = new LinkedHashSet<>(); // stores
// in input order
/*
* You can use treeset to store data in custom order, in this case
* lexicographically
*/
TreeSet<Variant> treeSet = new TreeSet<>(new VariantComparator());
}
}

overriding equals and hashcode methods in java?

I have below class.
Request.java
public class Request implements Serializable {
private String id;
private String name;
private String hid;
// getters and setters
// This class does not override any equals() and hashCode() methods
}
public class EmpRequest implements Serializable {
private Request request;
//Now here in this class I need override equals() and hashCode() methods based on **request**
}
In EmpRequest class, I need to override equals() and hashCode() based on properties of Request object.
If two request objects id is equal then i need to return true.
If two objects ids are not equal then i need to check for name and hid properties.
If name and hid properties of both the objects are equals then i need to return true.
Else false
How can I do that? I tried overriding equals() and hashCode() but eclipse gave me below the warning.
The field type 'com.mycompany.Request' does not implement equals() and hashCode() - the resulting code may not work correctly.
At the same type I cannot modify Request class as I don't have control over it.
How can I write equals() and hashCode() considering above conditions?

you can just generate equals() and hashCode() from IDE (Eclipse, IntelliJ IDEA) . That will enough for your scenario.
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof Result)) return false;
Result result = (Result) o;
if (hid != null ? !hid.equals(result.hid) : result.hid != null) return false;
if (id != null ? !id.equals(result.id) : result.id != null) return false;
if (name != null ? !name.equals(result.name) : result.name != null) return false;
return true;
}
#Override
public int hashCode() {
int result = id != null ? id.hashCode() : 0;
result = 31 * result + (name != null ? name.hashCode() : 0);
result = 31 * result + (hid != null ? hid.hashCode() : 0);
return result;
}

Edit:
public class Request implements Serializable{
private String id;
private String name;
private String hid;
public String getId()
{
return id;
}
public String getName()
{
return name;
}
public String getHid()
{
return hid;
}
}
public class EmpRequest implements Serializable{
private Request request;
public Request getRequest()
{
return request;
}
#Override
public boolean equals(Object obj) {
if(obj==null)
return false;
if(((EmpRequest) obj).getRequest().getId().equals(this.getRequest().getId()))
return true;
else if(((EmpRequest) obj).getRequest().getName().equals(this.getRequest().getName())
&&((EmpRequest) obj).getRequest().getHid().equals(this.getRequest().getHid())) {
return true;
}
else
return false;
}
}
Here is the hashcode too:
#Override
public int hashCode()
{
final int prime = 31;
int result = 1;
result = prime * result + ((getRequest().getId() == null) ? 0 : getRequest().getId().hashCode());
result = prime * result + ((getRequest().getName() == null) ? 0 : getRequest().getName().hashCode());
result = prime * result + ((getRequest().getHid() == null) ? 0 : getRequest().getHid().hashCode());
return result;
}

Method that adds elements to set always throwing custom exception

Ok, so I've got a method which adds elements to a list but it is always throwing my custom exception, no matter what, even when there are no elements in the Set I made.
private Set<Plan> planSet = new HashSet<Plan>();
public Plan createPlan(String name) throws DuplicatePlan{
Plan plan = new Plan(name);
if(!planSet.contains(plan)){
planSet.add(plan);
} else {
throw(new DuplicatePlan("Error, duplicate plan"));
}
return plan;
}
I'm thinking that my equals() and hashCode() methods are causing this. Currently I'm using the default overridden Eclipse hashCode() and equals(), this is what I've got there:
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((name == null) ? 0 : name.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;
}
Plan other = (Plan) obj;
if (name == null) {
if (other.name != null){
return false;
}
} else if (!name.equals(other.name)){
return false;
}
return true;
}
This is what Plan does:
private String name;
private Set<Tables> tablesSet;
public Plan(String name){
this.name = name ;
}
Here's what's supposed to happen if a user sets the same name in the TextField:
newPlan.setOnAction(new EventHandler<ActionEvent>(){
#Override
public void handle(ActionEvent action){
if(!newPlan.getText().isEmpty()){
try {
String name = planName.getText();
plan.createPLan(name);
esquema = esquemas.createPlan(planName.getText());
optionsPlans.getItems().add(plan.getName());
} catch (DuplicatePlan e) {
dialog.errorDialog(planError, duplicate);
}
} else {
dialog.errorDialog(empty, emptySpace);
}
}
});

Had to use Answer because it was too long for comment.
This here looks suspicious to me:
String name = planName.getText();
plan.createPLan(name);
esquema = esquemas.createPlan(planName.getText());
I.e. what's up with createPLan and createPlan? Copy & paste error? Or are you calling the same method twice (which would explain the behavior)?

How to sort an ArrayList using multiple sorting criteria?

I have an array list that contains Quote objects. I want to be able to sort alphabetically by name, by change, and by percent change. How can I sort my arraylist?
package org.stocktwits.model;
import java.io.Serializable;
import java.text.DecimalFormat;
public class Quote implements Serializable {
private static final long serialVersionUID = 1L;
public String symbol;
public String name;
public String change;
public String percentChange;
public String open;
public String daysHigh;
public String daysLow;
public String dividendYield;
public String volume;
public String averageDailyVolume;
public String peRatio;
public String marketCapitalization;
public String yearHigh;
public String yearLow;
public String lastTradePriceOnly;
public DecimalFormat df = new DecimalFormat("#,###,###,###,###,##0.00");
public DecimalFormat vf = new DecimalFormat("#,###,###,###,###,##0");
public String getSymbol() {
return symbol;
}
public void setSymbol(String symbol) {
this.symbol = symbol;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getChange() {
return change;
}
public void setChange(String change) {
if(change.equals("null")){
this.change = "N/A";
}
else{
float floatedChange = Float.valueOf(change);
this.change = (df.format(floatedChange));
}
}
public String getPercentChange() {
return percentChange;
}
public void setPercentChange(String percentChange) {
if(percentChange.equals("null"))
percentChange = "N/A";
else
this.percentChange = percentChange;
}
public String getOpen() {
return open;
}
public void setOpen(String open) {
if(open.equals("null"))
this.open = "N/A";
else
this.open = open;
}
public String getDaysHigh() {
return daysHigh;
}
public void setDaysHigh(String daysHigh) {
if(daysHigh.equals("null"))
this.daysHigh = "N/A";
else{
float floatedDaysHigh = Float.valueOf(daysHigh);
this.daysHigh = (df.format(floatedDaysHigh));
}
}
public String getDaysLow() {
return daysLow;
}
public void setDaysLow(String daysLow) {
if(daysLow.equals("null"))
this.daysLow = "N/A";
else{
float floatedDaysLow = Float.valueOf(daysLow);
this.daysLow = (df.format(floatedDaysLow));
}
}
public String getVolume() {
return volume;
}
public void setVolume(String volume) {
if(volume.equals("null")){
this.volume = "N/A";
}
else{
float floatedVolume = Float.valueOf(volume);
this.volume = (vf.format(floatedVolume));
}
}
public String getDividendYield() {
return dividendYield;
}
public void setDividendYield(String dividendYield) {
if(dividendYield.equals("null"))
this.dividendYield = "N/A";
else
this.dividendYield = dividendYield;
}
public String getAverageDailyVolume() {
return averageDailyVolume;
}
public void setAverageDailyVolume(String averageDailyVolume) {
if(averageDailyVolume.equals("null")){
this.averageDailyVolume = "N/A";
}
else{
float floatedAverageDailyVolume = Float.valueOf(averageDailyVolume);
this.averageDailyVolume = (vf.format(floatedAverageDailyVolume));
}
}
public String getPeRatio() {
return peRatio;
}
public void setPeRatio(String peRatio) {
if(peRatio.equals("null"))
this.peRatio = "N/A";
else
this.peRatio = peRatio;
}
public String getMarketCapitalization() {
return marketCapitalization;
}
public void setMarketCapitalization(String marketCapitalization) {
if(marketCapitalization.equals("null"))
this.marketCapitalization = "N/A";
else
this.marketCapitalization = marketCapitalization;
}
public String getYearHigh() {
return yearHigh;
}
public void setYearHigh(String yearHigh) {
if(yearHigh.equals("null"))
this.yearHigh = "N/A";
else
this.yearHigh = yearHigh;
}
public String getYearLow() {
return yearLow;
}
public void setYearLow(String yearLow) {
if(yearLow.equals("null"))
this.yearLow = "N/A";
else
this.yearLow = yearLow;
}
public String getLastTradePriceOnly() {
return lastTradePriceOnly;
}
public void setLastTradePriceOnly(String lastTradePriceOnly) {
if(lastTradePriceOnly.equals("null")){
this.lastTradePriceOnly = "N/A";
}
else{
float floatedLastTradePriceOnly = Float.valueOf(lastTradePriceOnly);
this.lastTradePriceOnly = (df.format(floatedLastTradePriceOnly));
}
}
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((change == null) ? 0 : change.hashCode());
result = prime * result
+ ((daysHigh == null) ? 0 : daysHigh.hashCode());
result = prime * result + ((daysLow == null) ? 0 : daysLow.hashCode());
result = prime
* result
+ ((lastTradePriceOnly == null) ? 0 : lastTradePriceOnly
.hashCode());
result = prime
* result
+ ((marketCapitalization == null) ? 0 : marketCapitalization
.hashCode());
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result + ((open == null) ? 0 : open.hashCode());
result = prime * result + ((peRatio == null) ? 0 : peRatio.hashCode());
result = prime * result
+ ((percentChange == null) ? 0 : percentChange.hashCode());
result = prime * result + ((symbol == null) ? 0 : symbol.hashCode());
result = prime * result + ((volume == null) ? 0 : volume.hashCode());
result = prime * result
+ ((yearHigh == null) ? 0 : yearHigh.hashCode());
result = prime * result + ((yearLow == null) ? 0 : yearLow.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;
Quote other = (Quote) obj;
if (change == null) {
if (other.change != null)
return false;
} else if (!change.equals(other.change))
return false;
if (daysHigh == null) {
if (other.daysHigh != null)
return false;
} else if (!daysHigh.equals(other.daysHigh))
return false;
if (daysLow == null) {
if (other.daysLow != null)
return false;
} else if (!daysLow.equals(other.daysLow))
return false;
if (lastTradePriceOnly == null) {
if (other.lastTradePriceOnly != null)
return false;
} else if (!lastTradePriceOnly.equals(other.lastTradePriceOnly))
return false;
if (marketCapitalization == null) {
if (other.marketCapitalization != null)
return false;
} else if (!marketCapitalization.equals(other.marketCapitalization))
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
if (open == null) {
if (other.open != null)
return false;
} else if (!open.equals(other.open))
return false;
if (peRatio == null) {
if (other.peRatio != null)
return false;
} else if (!peRatio.equals(other.peRatio))
return false;
if (percentChange == null) {
if (other.percentChange != null)
return false;
} else if (!percentChange.equals(other.percentChange))
return false;
if (symbol == null) {
if (other.symbol != null)
return false;
} else if (!symbol.equals(other.symbol))
return false;
if (volume == null) {
if (other.volume != null)
return false;
} else if (!volume.equals(other.volume))
return false;
if (yearHigh == null) {
if (other.yearHigh != null)
return false;
} else if (!yearHigh.equals(other.yearHigh))
return false;
if (yearLow == null) {
if (other.yearLow != null)
return false;
} else if (!yearLow.equals(other.yearLow))
return false;
return true;
}
}

If you (almost) always want to use that order you can add the Comparable interface to Quote and implement a compareTo method.
public int compareTo(Quote quote) {
int result = this.getName().compareTo(quote.getName());
if (result == 0) {
result = this.getChange().compareTo(quote.getChange());
}
if (result == 0) {
result = this.getPercentChange().compareTo(quote.getPercentChange());
}
return result;
}
Then use a sorted collection, or sort a list, and the quotes will be sorted.
For ad hoc sorting, a separate, possibly anonymous, Comparator is better.

Everybody is right that you want to use Comparators. Extending on that idea, if you want to be able to sort on multiple criteria, then a class like this will work for you:
public class MultiComparator<T> implements Comparator<T> {
private List<Comparator<T>> comparators;
public MultiComparator(List<Comparator<T>> comparators) {
this.comparators = comparators;
}
public int compare(T o1, T o2) {
for (Comparator<T> comparator : comparators) {
int comparison = comparator.compare(o1, o2);
if (comparison != 0) return comparison;
}
return 0;
}
}
Then you just write really simple comparators for whichever fields you desire and you can combine them into more complex comparators more easily and with more reuse.

Have a look at the ComparatorChain from the Apache Commons Collection. This should do the job. Don't implement logic if is already available and tested.
At the following site I have a tutorial: Sorting Objects By Multiple Attributes"

Create an appropiate Comparator that will compare two items according to your desired criteria. Then use Collections.sort() on your ArrayList.
If at a later time you want to sort by different criteria, call Collections.sort() again with a different Comparator.

Sun has devoted big part of its tutorial to sorting in Java collections:
http://download.oracle.com/javase/tutorial/collections/interfaces/order.html
It discusses both Comparable and Comparator interfaces with examples.

See Collections.sort with an explicit Comparator (or the Collections.sort kind that requires the input to implement Comparable, if you prefer).

There are two things:
Sorting on multiple fields of an object
Multilevel sorting (Here sorting done on first field and then next sorting applied on grouping done on similar items in previous sort)
For #2: I found this below article very much close to what i desire
http://strangeoptics.blogspot.com/2011/09/sorting-objects-by-multiple-attributes.html