The document discusses the differences between Java and Kotlin in terms of class structure, property management, and null handling. It showcases code examples for creating articles and members in both languages, emphasizing aspects like getters, setters, and dependency injection. Additionally, it reflects on annotations, compile-time checks, and various coding practices in both programming environments.

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21. // Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public String getTitle() {
return this.title;
}
public void setTitle(String title) {
this.title = title;
}
@Override
public String toString() { ... }
...
}

22. // Kotlin
data class Aritcle(
var articleId: Int? = null,
var viewCount: Int = 0,
var title: String = “”
...
)
// Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public String getTitle() {
return this.title;
}
public void setTitle(String title) {
this.title = title;
}
@Override
public String toString() { ... }
...
}

23. // Kotlin
data class Aritcle(
var articleId: Int? = null,
var viewCount: Int = 0,
var title: String = “”
...
)
// Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public String getTitle() {
return this.title;
}
public void setTitle(String title) {
this.title = title;
}
@Override
public String toString() { ... }
...
}
getter()
setter()

24. // Kotlin
data class Aritcle(
var articleId: Int? = null,
var viewCount: Int = 0,
var title: String = “”
...
)
// Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public String getTitle() {
return this.title;
}
public void setTitle(String title) {
this.title = title;
}
@Override
public String toString() { ... }
...
}
equals()
hashCode()
copy()
toString()
componentsN()

25. // Kotlin
data class Aritcle(
var articleId: Int? = null,
var viewCount: Int = 0,
var title: String = “”
...
)
// Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public String getTitle() {
return this.title;
}
public void setTitle(String title) {
this.title = title;
}
@Override
public String toString() { ... }
...
}

26. // Kotlin
data class Aritcle(
var articleId: Int? = null,
var viewCount: Int = 0,
var title: String = “”
...
)
// Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public String getTitle() {
return this.title;
}
public void setTitle(String title) {
this.title = title;
}
@Override
public String toString() { ... }
...
}

27. // Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public void setViewCount(int viewCount) {
this.viewCount = viewCount;
}
}
// use case
Integer nullableNum = null;
article.setViewCount(nullableNum);

28. // Java
public class Member {
private Integer memberId;
private int age;
private String name;
public void setMemberId(Integer memberId) {
if(memberId == null) {
// do something
}
this.memberId = memberId;
}
...
}
Integer nullableNumber = null;
member.setAge(nullableNumber);
// runtime error!!
// Kotlin
data class Aritcle(
var articleId: Int? = null,
var viewCount: Int = 0,
var title: String = “”
...
)
// use case
var nullableNum: Int? = null
article.viewcount = nullableNum
// Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public void setViewCount(int viewCount) {
this.viewCount = viewCount;
}
}
// use case
Integer nullableNum = null;
article.setViewCount(nullableNum);

29. // Java
public class Member {
private Integer memberId;
private int age;
private String name;
public void setMemberId(Integer memberId) {
if(memberId == null) {
// do something
}
this.memberId = memberId;
}
...
}
Integer nullableNumber = null;
member.setAge(nullableNumber);
// runtime error!!
// Kotlin
data class Aritcle(
var articleId: Int? = null,
var viewCount: Int = 0,
var title: String = “”
...
)
// use case
var nullableNumber: Int? = null
article.viewcount = nullableNumber
// Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public void setViewCount(int viewCount) {
this.viewCount = viewCount;
}
}
// use case
Integer nullableNum = null;
article.setViewCount(nullableNum);

30. // Java
public class Article {
private Integer articleId;
private int viewCount;
private String title;
...
public void setViewCount(int viewCount) {
this.viewCount = viewCount;
}
}
Integer nullableNum = null;
article.setViewCount(nullableNum);
// Kotlin
data class Aritcle(
var articleId: Int? = null,
var viewCount: Int = 0,
var title: String = “”
...
)
// use case
var nullableNum: Int? = null
article.viewcount = nullableNum

44. // Java
@Getter
@Setter
public class Article {
private Integer articleId;
private int viewCount;
private String title;
}
// auto-converted kotlin
@Getter
@Setter
class Article {
private val articleId : Int? = null
private val viewCount : Int = 0
private val title : String? = null
}

45. // Java
@Getter
@Setter
public class Article {
private Integer articleId;
private int viewCount;
private String title;
}
// auto-converted kotlin
@Getter
@Setter
class Article {
private val articleId : Int? = null
private val viewCount : Int = 0
private val title : String? = null
}
public getter()
public setter()

46. // Java
@Getter
@Setter
public class Article {
private Integer articleId;
private int viewCount;
private String title;
}
// auto-converted kotlin
@Getter
@Setter
class Article {
private val articleId : Int? = null
private val viewCount : Int = 0
private val title : String? = null
}
동작하지 않는 Annotation

47. // Java
@Getter
@Setter
public class Article {
private Integer articleId;
private int viewCount;
private String title;
}
// auto-converted kotlin
@Getter
@Setter
class Article {
private val articleId : Int? = null
private val viewCount : Int = 0
private val title : String? = null
}
외부에서 참조 불가능한 properties

56. // Java without Lombok
public class Article {
private Integer articleId;
private int viewCount;
private String title;
public Integer getMemberId() {
return this.memberId;
}
...
}
// Java with Lombok
@Data
public class Article {
private Integer articleId;
private int viewCount;
private String title;
}

57. // auto-converted Kotlin
class Article {
var articleId: Int? = null
var viewCount: Int = 0
var title: String? = null
override fun toString(): String {
return “Article{”
+ “articleId=“ + articleId
+ “, viewCount=” + viewCount
+ “, title=‘” + title
+ ‘’’.toString() + ‘}’.toString()
} ...
}
// Java without Lombok
public class Article {
private Integer articleId;
private int viewCount;
private String title;
public Integer getMemberId() {
return this.memberId;
}
...
}

58. // refactored Kotlin
data class Article (
var articleId: Int? = null
var viewCount: Int = 0
var title: String = “”
)
// auto-converted Kotlin
class Article {
var articleId: Int? = null
var viewCount: Int = 0
var title: String? = null
override fun toString(): String {
return “Article{”
+ “articleId=“ + articleId
+ “, viewCount=” + viewCount
+ “, title=‘” + title
+ ‘’’.toString() + ‘}’.toString()
} ...
}

60. @Slf4j
public class LogExaple {
}
// Java
@Controller
public class ArticleController {
@Autowired
private ArticleService articleService;
@Autowired
private TagService tagService;
}
@Slf4j
public class LogExaple {
}
// Kotlin
@Controller
class ArticleController {
@Autowired
private var articleService : ArticleService
@Autowired
private var tagService : TagService
}
동작하지 않는 필드 주입

61. @Slf4j
public class LogExaple {
}
// Java
@Controller
public class ArticleController {
@Autowired
private ArticleService articleService;
@Autowired
private TagService tagService;
}
@Slf4j
public class LogExaple {
}
// Kotlin
@Controller
class ArticleController {
@Autowired
private var articleService : ArticleService?
= null
@Autowired
private var tagService : TagService?
= null
}

62. @Slf4j
public class LogExaple {
}
// Java
@Controller
public class ArticleController {
@Autowired
private ArticleService articleService;
@Autowired
private TagService tagService;
}
@Slf4j
public class LogExaple {
}
// Kotlin
@Controller
class ArticleController {
@Autowired
private lateinit var articleService :
ArticleService
@Autowired
private lateinit var tagService : TagService
}

63. @Slf4j
public class LogExaple {
}
// Java
@Controller
public class ArticleController {
private final ArticleService articleService;
private final TagService tagService;
public ArticleController(
final ArticleService articleService,
final TagService tagService) {
this.articleService = articleService;
this.tagService = tagService;
}
}
@Slf4j
public class LogExaple {
}
// Kotlin
@Controller
class ArticleController(
private val articleService : ArticleService,
private val tagService : TagService) {
}

64. @Slf4j
public class LogExaple {
}
@RequestMapping(“/”)
@Controller
class SearchController {
@GetMapping
fun search(@RequestParam(required = true) keyword : String?) { // Java와 동일하게 사용
return “/result”
}
}
필수로 명시하였지만 Optional로 동작

65. @Slf4j
public class LogExaple {
}
@RequestMapping(“/”)
@Controller
class SearchController {
@GetMapping
fun search(@RequestParam keyword : String) {
return “/result”
}
}

66. @Slf4j
public class LogExaple {
}
// Java
public class Article {
public static final String DEFAULT_THUMBNAIL
= “..”;
...
public static String thumbnail() {
...
}
...
}
// Kotlin
class Article {
companion object {
val DEFAULT_THUMBNAIL = “..”
fun thumbnail(): String {
...
}
}
...
}

67. @Slf4j
public class LogExaple {
}
// Java
public class Article {
public static final String DEFAULT_THUMBNAIL
= “..”;
...
public static String thumbnail() {
...
}
...
}
// Kotlin
class Article {
companion object {
const val DEFAULT_THUMBNAIL = “..”
@JvmStatic
fun thumbnail(): String {
...
}
}
...
}

70. @Slf4j
public class LogExaple {
} when (x) {
0, 1 -> print("x == 0 or x == 1")
parseInt(s) -> print("s encodes x")
isEven() -> print("x is even")
in 1..10 -> print("x is in the range")
in validNumbers -> print("x is valid")
is String -> x.startsWith("prefix")
else -> print("otherwise")
}

71. @Slf4j
public class LogExaple {
}
//Java
if (isFromRobot(userAgent)) {
return false;
} else if (isValidUser(cookie)) {
return false;
} else {
return true;
}
//Kotlin
return when {
isFromRobot(userAgent) -> false
isValidUser(cookie) -> false
else -> ture
}

72. @Slf4j
public class LogExaple {
}

73. //Kotlin
@Controller
class ArticleController {
…
@GetMapping(“/article/{articleId}”)
fun blog(model: Model, @PathVariable articleId : String): String {
Article article = articleRepository.find(articleId)
model["title"] = article.title //model.addAttribute("title", article.title)
return “article"
}
}

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79. //Java
@Service
public class JavaController {
@Autowired
private JavaService javaService;
..
}
//Kotlin
@Service
class KotlinController(private val kotlinService: KotlinService)
{
..
}

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438
402

81. //Java
var imgUrl: String = DEFAILT_IMG_URL
if (isMediaType()) {
imgUrl = media.getThumbnail()
} else if (hasMediaHolder()) {
imgUrl = getHolder()
} else if {
…
}
//Kotlin
val imgUrl = when {
isMediaType() -> media.thumbnail
hasMediaHolder() -> getHolder()
…
else -> DEFAILT_IMG_URL
}

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217
205 205

83. //Java
List<Menu> displayedMainMenus = MainMenus.stream()
.filter(e -> e.getDisplayed())
.collect(Collectors.toList());
//Kotlin
val displayedMainMenus: List<Menu>
= mainMenus.filter { it.displayed }