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自從谷歌I/O 2017宣布將支持Kotlin作為Android開發(fā)的First-Class語(yǔ)言,，相信各位程序員的朋友圈都被Kotlin的消息轟炸了吧,，支持Java的“守舊派”認(rèn)為Java將穩(wěn)坐霸主地位不動(dòng)搖,，支持Kotlin的“維新派”認(rèn)為Kotlin很可能會(huì)把Java拉下馬。 其實(shí),，筆者認(rèn)為新語(yǔ)言的出現(xiàn)對(duì)于程序員來(lái)說(shuō)并不是一件新鮮事兒,，程序員始終踐行著“活到老，學(xué)到老”,，真正能夠?qū)Τ绦騿T產(chǎn)生影響的新語(yǔ)言的使用和性能,。 GitHub用戶amitshekhariitbhu在GitHub上貼圖分享了Java和Kotlin的語(yǔ)法區(qū)別，下面我們就一起來(lái)看一下吧! Java System.out.print("Amit Shekhar"); System.out.println("Amit Shekhar"); Kotlin print("Amit Shekhar") println("Amit Shekhar") Java String name = "Amit Shekhar"; final String name = "Amit Shekhar"; Kotlin var name = "Amit Shekhar" val name = "Amit Shekhar" Java String otherName; otherName = null; Kotlin var otherName : String? otherName = null Java if (text != null) { int length = text.length(); } Kotlin text?.let { val length = text.length } Java String firstName = "Amit"; String lastName = "Shekhar"; String message = "My name is: " + firstName + " " + lastName; Kotlin val firstName = "Amit" val lastName = "Shekhar" val message = "My name is: $firstName $lastName" Java String text = "First Line\n" + "Second Line\n" + "Third Line"; Kotlin val text = """ |First Line |Second Line |Third Line """.trimMargin() Java String text = x > 5 ? "x > 5" : "x <= 5"; Kotlin val text = if (x > 5) "x > 5" else "x <= 5" Java if (object instanceof Car) { } Car car = (Car) object; Kotlin if (object is Car) { } var car = object as Car Java if (object instanceof Car) { Car car = (Car) object; } Kotlin if (object is Car) { var car = object // smart casting } Java if (score >= 0 && score <= 300) { } Kotlin if (score in 0..300) { } Java int score = // some score; String grade; switch (score) { case 10: case 9: grade = "Excellent"; break; case 8: case 7: case 6: grade = "Good"; break; case 5: case 4: grade = "Ok"; break; case 3: case 2: case 1: grade = "Fail"; break; default: grade = "Fail"; } Kotlin var score = // some score var grade = when (score) { 9, 10 -> "Excellent" in 6..8 -> "Good" 4, 5 -> "Ok" in 1..3 -> "Fail" else -> "Fail" } Java for (int i = 1; i <= 10 ; i++) { } for (int i = 1; i < 10 ; i++) { } for (int i = 10; i >= 0 ; i--) { } for (int i = 1; i <= 10 ; i+=2) { } for (int i = 10; i >= 0 ; i-=2) { } for (String item : collection) { } for (Map.Entry<String, String> entry: map.entrySet()) { } Kotlin for (i in 1..10) { } for (i in 1 until 10) { } for (i in 10 downTo 0) { } for (i in 1..10 step 2) { } for (i in 10 downTo 1 step 2) { } for (item in collection) { } for ((key, value) in map) { } Java final List<Integer> listOfNumber = Arrays.asList(1, 2, 3, 4); final Map<Integer, String> keyValue = new HashMap<Integer, String>(); map.put(1, "Amit"); map.put(2, "Ali"); map.put(3, "Mindorks"); // Java 9 final List<Integer> listOfNumber = List.of(1, 2, 3, 4); final Map<Integer, String> keyValue = Map.of(1, "Amit", 2, "Ali", 3, "Mindorks"); Kotlin val listOfNumber = listOf(1, 2, 3, 4) val keyValue = mapOf(1 to "Amit", 2 to "Ali", 3 to "Mindorks") Java // Java 7 and below for (Car car : cars) { www.auromcs.cn; System.out.println(car.speed); } // Java 8+ cars.forEach(car -> System.out.println(car.speed)); // Java 7 and below for (Car car : cars) { if (car.speed > 100) { System.out.println(car.speed); } } // Java 8+ cars.stream().filter(car -> car.speed > 100).forEach(car -> System.out.println(car.speed)); Kotlin cars.forEach { println(it.speed) } cars.filter { it.speed > 100 } .forEach { println(it.speed)} Java void doSomething() { // logic here } Kotlin fun doSomething() { // logic here } Java void doSomething(int... numbers) { // logic here } Kotlin fun doSomething(vararg numbers: Int) { // logic here } Java int getScore() { // logic here return score; } Kotlin fun getScore(): Int { // logic here return score } // as a single-expression function fun getScore(): Int = score Java int getScore(int value) { // logic here return 2 * value; } Kotlin fun getScore(value: Int): Int { // logic here return 2 * value } // as a single-expression function fun getScore(value: Int): Int = 2 * value Java public class Utils { private Utils() { // This utility class is not publicly instantiable } public static int getScore(int value) { return 2 * value; } } Kotlin class Utils private constructor() { companion object { fun getScore(value: Int): Int { return 2 * value } } } // other way is also there object Utils { fun getScore(value: Int): Int { return 2 * value } } Java public class Developer { private String name; private int age; public Developer(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Developer developer = (Developer) o; if (age != developer.age) return false; return name != null ? name.equals(developer.name) : developer.name == null; } @Override public int hashCode() { int result = name != null ? name.hashCode() : 0; result = 31 * result + age; return result; } @Override public String toString() { return "Developer{" + "name='" + name + '\'' + ", age=" + age + '}'; } } Kotlin data class Developer(var name: String, var age: Int) Java public class Utils { private Utils() { // This utility class is not publicly instantiable } public static int triple(int value) { return 3 * value; } } int result = Utils.triple(3); Kotlin fun Int.triple(): Int { return this * 3 } var result = 3.triple()
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來(lái)自： 昵稱45065300 > 《待分類》
