CODEWITHSUNDEEP
javahashsetlinkedhashset
user3488019
user3488019

Reputation: 51

How to look though a list of Objects to find a match?

I'm trying to compare a bunch of Objects of the same class to search for matching ID's? This is the GroupClass, when a new entry is entered it will test against the idNumber to see if there is a match.

Public GroupClass {

private int idNumber;
private String name;
private double income;


public GroupClass(int id, String name, double income){
    this.idNumber = id;
    this.name = name;
    this.income = income;
}

public int getIdNumber() {
    return idNumber;
}

public void setIdNumber(int idNumber) {
    this.idNumber = idNumber;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public double getIncome() {
    return income;
}

public void setIncome(double income) {
    this.income = income;
 }
}

This is the Main Method

import static java.lang.reflect.Array.set;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Scanner;
import java.util.Set;


    public class ListTester {
    public static void main(String[] args) {
    Scanner input = new Scanner(System.in);

    Set<GroupClass> groupArray = new LinkedHashSet<>();
    System.out.println("Enter a ID Number");
    int id = input.nextInt();
    System.out.println("Enter a First Name");
    String name = input.next();
    System.out.println("Enter a an Income");
    double income = input.nextDouble();


    groupArray.add(new GroupClass(1111, "Billy", 178000));
    groupArray.add(new GroupClass(1112, "Sam", 78000));
    groupArray.add(new GroupClass(1113, "Mark", 79000));

    groupArray.add(new GroupClass(id, name, income));
    printTheClass(groupArray);


}

public static void printTheClass(Set group){
    for(Object theArray: group){
        System.out.println(theArray + " ");
    }
}

}

Ive seen a few questions like it but just cant get it to work for my particular case, thanks in advance.

Upvotes: 0

Views: 66

Answers (2)

lnyng
lnyng

Reputation: 965

Not quite sure what is your goal. If you want to reject any new entry if the id already exist, you need to override the hashCode and equals methods of the GroupClass so that LinkedHashSet knows if two GroupClass objects are different:

@Override
public int hashCode() {
    return this.idNumber;
}

@Override
public boolean equals(Object obj) {
    return obj instanceof GroupClass && ((GroupClass) obj).getIdNumber() == this.idNumber;
}

However, in most cases, you might want to retrieve an entry using its id number. Then it might be better to use a map with id as key, and the GroupoClass object itself as value

Map<Integer, GroupClass> groupmap = new HashMap<>()
groupmap.put(id, new GroupClass(id, name, income));

and you will have to use groupmap.keySet() to iterate the map.

Upvotes: 0

Scary Wombat
Scary Wombat

Reputation: 44854

As per the above comment you override the equals method, but this may not be suitable for the long term growth of the class.

But using your existing code try

public static void printTheClass(Set<GroupClass> group){
    for(GroupClass theArray: group){
        System.out.println(theArray + " ");
    }
}

and 

public static GroupClass findTheClass(Set<GroupClass> group, int id){
    for(GroupClass obj: group){
        if(obj.getIdNumber == id) return obj;
    }
    return null;
}

This can be used as

if (findTheClass (groupArray, id) == null) {
  groupArray.add (new GroupClass(id, name, income));
}

Upvotes: 1

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