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Which methods do we need to override to use an object as key in a HashMap?

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Pragya Keshap answered on February 4, 2023 Popularity 3/10 Helpfulness 1/10

answer Which methods do we need to override to use an object as key in a HashMap?

Which methods do we need to override to use an object as key in a HashMap?

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If we want to use an object as a key in a HashMap in Java, then we

have to make sure that it has the implementation of equals() and

hashCode() methods.

class Employee
{
    private String name;
    private int age;
 
    public Employee(String name, int age)
    {
        this.name = name;
        this.age = age;
    }
 
    @Override
    public boolean equals(Object o)
    {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
 
        Employee employee = (Employee) o;
 
        if (age != employee.age) {
            return false;
        }
        if (!name.equals(employee.name)) {
            return false;
        }
 
        return true;
    }
 
    @Override
    public int hashCode()
    {
        int result = name.hashCode();
        result = 31 * result + age;
        return result;
    }
 
    @Override
    public String toString()
    {
        return "{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
 
class Main
{
    public static void main(String[] args)
    {
        Employee e1 = new Employee("John", 20);
        Employee e2 = new Employee("John", 20);
 
        Set<Employee> employees = new HashSet<>();
        employees.add(e1);
        employees.add(e2);
 
        System.out.println(employees);
    }
}

https://www.techiedelight.com/use-object-as-key-hashmap-hashset-java/#:~:text=Therefore%2C%20to%20use%20an%20object,check%20for%20the%20instance%20equality.

Popularity 3/10 Helpfulness 1/10 Language java

Source: Grepper

Tags: java key methods object

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Contributed on Feb 04 2023

Pragya Keshap

0 Answers Avg Quality 2/10

Which methods do we need to override to use an object as key in a HashMap?

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