SOLID - Interface Segregation Principle

/* Interface Segregation Principle */

// Before
class Person {

    private final String firstName;
    private final String lastName;
    private final float gpa;
    private final String accountNumber;

    public Person(String firstName, String lastName, float gpa, String accountNumber) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.gpa = gpa;
        this.accountNumber = accountNumber;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public float getGpa() {
        return gpa;
    }

    public String getAccountNumber() {
        return accountNumber;
    }

}

class Accountant {

    public void paySalary(Person person) {
        System.out.println("Account number: " + person.getAccountNumber());
    }

}

// After
interface Employee {

    public String getFirstName();

    public String getLastName();

    public String getAccountNumber();

}

interface Student {

    public String getFirstName();

    public String getLastName();

    public float getGpa();

}

class Person implements Student, Employee {

    private final String firstName;
    private final String lastName;
    private final float gpa;
    private final String accountNumber;

    public Person(String firstName, String lastName, float gpa, String accountNumber) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.gpa = gpa;
        this.accountNumber = accountNumber;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public float getGpa() {
        return gpa;
    }

    public String getAccountNumber() {
        return accountNumber;
    }

}

class Accountant {

    public void paySalary(Employee employee) {
        System.out.println("Account number: " + employee.getAccountNumber());
    }

}