함수형 프로그래밍 with 자바 - POJO 와 불변POJO 그리고 record

함수형 프로그램을 위해

SAM (Single Abstract Method ) 필요

불변성 유지 필요 ( record 로 구현함 jdk 14 미리보기 에 나옴 )

 

POJO 를 이용한 불변성 구현

 

1. 일반

package kr.samdogs.study.func.pojo;

import java.time.LocalDateTime;
import java.util.Objects;

//변경불가능 유지를 위해 final class
public final class User {
	private String username;
	private boolean active;
	private LocalDateTime lastLogin;
	
	public User(String username,
			boolean active,
			LocalDateTime lastLogin) {
		this.username = username;
		this.active = active;
		this.lastLogin = lastLogin;
	}

	/* getter setter, hashCode, equals 이클립스 자동생성  */
	public void setUsername(String username) {
		this.username = username;
	}

	public void setActive(boolean active) {
		this.active = active;
	}

	public void setLastLogin(LocalDateTime lastLogin) {
		this.lastLogin = lastLogin;
	}

	public String getUsername() {
		return username;
	}

	public boolean isActive() {
		return active;
	}

	public LocalDateTime getLastLogin() {
		return lastLogin;
	}

	@Override
	public int hashCode() {
		return Objects.hash(active, lastLogin, username);
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		User other = (User) obj;
		return active == other.active && Objects.equals(lastLogin, other.lastLogin)
				&& Objects.equals(username, other.username);
	}
	
	//자동생성에서 조금 수정함
	@Override
	public String toString() {
		return new StringBuilder().append("User [username=")
				.append(username)
				.append(", active=")
				.append(active)
				.append(", lastLogin=")
				.append(lastLogin)
				.append("]").toString();
	}
	
	
}

 

2. 불변 POJO 만들기

package kr.samdogs.study.func.pojo;

import java.time.LocalDateTime;
import java.util.Objects;

//변경불가능 유지를 위해 final class
public final class User {
	//변수의 불변을 위해 final 추가
	private final String username;
	private final boolean active;
	private final LocalDateTime lastLogin;
	
	public User(String username,
			boolean active,
			LocalDateTime lastLogin) {
		this.username = username;
		this.active = active;
		this.lastLogin = lastLogin;
	}

	/* getter setter, hashCode, equals 이클립스 자동생성  */
	// 불변변수이므로 set 함수 삭제
	public String getUsername() {
		return username;
	}

	public boolean isActive() {
		return active;
	}

	public LocalDateTime getLastLogin() {
		return lastLogin;
	}

	@Override
	public int hashCode() {
		return Objects.hash(active, lastLogin, username);
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		User other = (User) obj;
		return active == other.active && Objects.equals(lastLogin, other.lastLogin)
				&& Objects.equals(username, other.username);
	}
	
	//자동생성에서 조금 수정함
	@Override
	public String toString() {
		return new StringBuilder().append("User [username=")
				.append(username)
				.append(", active=")
				.append(active)
				.append(", lastLogin=")
				.append(lastLogin)
				.append("]").toString();
	}
	
	
}

 

3. record 이용해서 만들기 (JDK14 이상부터 가능)

public record User(String username,
			boolean active,
			LocalDateTime lastLogin) {
            //생략
}