全网最细笔记java与kotlin的一些异同

本文主要介绍java与kotlin的一些异同

后面可能还会继续比较kotlin和dart 期待吗？

打印日志

Java

System.out.print("Amit Shekhar");
System.out.println("Amit Shekhar");

Kotlin

print("Amit Shekhar")
println("Amit Shekhar")

常量与变量

Java

String name = "Amit Shekhar";
final String name = "Amit Shekhar";

Kotlin

var name = "Amit Shekhar"
val name = "Amit Shekhar"

null声明

Java

String otherName;
otherName = null;

Kotlin

var otherName : String?
otherName = null

空判断

Java

if (text != null) {int length = text.length();
}

Kotlin

text?.let {val length = text.length
}
// or simply
val length = text?.length

字符串拼接

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"

换行

Java

String text = "First Line\n" +"Second Line\n" +"Third Line";

Kotlin

val text = """|First Line|Second Line|Third Line""".trimMargin()

三元表达式

Java

String text = x > 5 ? "x > 5" : "x <= 5";

Kotlin

val text = if (x > 5)"x > 5"else "x <= 5"

操作符

java

final int andResult  = a & b;
final int orResult   = a | b;
final int xorResult  = a ^ b;
final int rightShift = a >> 2;
final int leftShift  = a << 2;
final int unsignedRightShift = a >>> 2;

Kotlin

val andResult  = a and b
val orResult   = a or b
val xorResult  = a xor b
val rightShift = a shr 2
val leftShift  = a shl 2
val unsignedRightShift = a ushr 2

类型判断和转换 (声明式)

Java

if (object instanceof Car) {
}
Car car = (Car) object;

Kotlin

if (object is Car) {
}
var car = object as Car

类型判断和转换 (隐式)

Java

if (object instanceof Car) {Car car = (Car) object;
}

Kotlin

if (object is Car) {var car = object // 聪明的转换
}

多重条件

Java

if (score >= 0 && score <= 300) { }

Kotlin

if (score in 0..300) { }

更灵活的case语句

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"
}

for循环

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 0 step 2) { }for (item in collection) { }for ((key, value) in map) { }

更方便的集合操作

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")

遍历

Java

// Java 7 and below
for (Car car : cars) {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)}

方法定义

Java

void doSomething() {// logic here
}void doSomething(int... numbers) {// logic here
}

Kotlin

fun doSomething() {// logic here
}fun doSomething(vararg numbers: Int) {// logic here
}

带返回值的方法

Java

int getScore() {// logic herereturn score;
}

Kotlin

fun getScore(): Int {// logic herereturn score
}// as a single-expression functionfun getScore(): Int = score

无结束符号

Java

int getScore(int value) {// logic herereturn 2 * value;
}

Kotlin

fun getScore(value: Int): Int {// logic herereturn 2 * value
}// as a single-expression functionfun getScore(value: Int): Int = 2 * value

constructor 构造器

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}}
}// another wayobject Utils {fun getScore(value: Int): Int {return 2 * value}}

Get Set 构造器

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;}@Overridepublic 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;}@Overridepublic int hashCode() {int result = name != null ? name.hashCode() : 0;result = 31 * result + age;return result;}@Overridepublic String toString() {return "Developer{" +"name='" + name + '\'' +", age=" + age +'}';}
}

Kotlin

data class Developer(val name: String, val age: Int)

原型扩展

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()

Java

public enum Direction {NORTH(1),SOUTH(2),WEST(3),EAST(4);int direction;Direction(int direction) {this.direction = direction;}public int getDirection() {return direction;}}

Kotlin

enum class Direction(val direction: Int) {NORTH(1),SOUTH(2),WEST(3),EAST(4);
}

完结撒花

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全网最细笔记java与kotlin的一些异同

打印日志

常量与变量

null声明

空判断

字符串拼接

换行

三元表达式

操作符

类型判断和转换 (声明式)

类型判断和转换 (隐式)

多重条件

更灵活的case语句

for循环

更方便的集合操作

遍历

方法定义

带返回值的方法

无结束符号

constructor 构造器

Get Set 构造器

原型扩展

全网最细笔记java与kotlin的一些异同相关推荐

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