Application layers

package com.example.demo2.businesslayer;

import javax.persistence.Entity;
import javax.persistence.Column;
import javax.persistence.Table;
import javax.persistence.Id;

@Entity 
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public class User {
	
    @Id
    private long id;

    @Column(name = "username")
    private String username;

    @Column(name = "firstName")
    private String firstName;

    @Column(name = "lastName")
    private String lastName;
	
    public User() {
		
    }
	
    public User(long id, String username, String firstName, String lastName) {
        this.id = id;
        this.username = username;
        this.firstName = firstName;
        this.lastName = lastName;
    }

    // getters and setters
}

@Entity
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class User(
    @Id
    var id: Long = 0,

    @Column(name = "username")
    var username: String? = null,

    @Column(name = "firstName")
    var firstName: String? = null,

    @Column(name = "lastName")
    var lastName: String? = null
)