这篇文章主要介绍“Kotlin与Java的异同点有哪些”，在日常操作中，相信很多人在Kotlin与Java的异同点有哪些问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”Kotlin与Java的异同点有哪些”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
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打印日志
Java
System.out.print("hello world");
System.out.println("hello world");
Kotlin
print("hello world")
println("hello world")
定义变量与常量常
Java
String name =
"hello world";
final String name =
"hello world";
Kotlin
var name =
"hello world"
val name =
"hello world"
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 =
"Android";
String lastName =
"Architect";
String message =
"My name is: " + firstName +
" " +
lastName;
Kotlin
val firstName =
"Android"
val lastName =
"Architect"
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
Car car = (Car)
object;
Kotlin
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 // 自动识别
}
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 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 listOfNumber = Arrays.asList(1,
2,
3,
4);
final Map keyValue =
new HashMap();
map.put(1,
"Android");
map.put(2,
"Ali");
map.put(3,
"Mindorks");
// Java 9
final List listOfNumber = List.of(1, 2, 3, 4);
final Map keyValue = Map.of(1, "Android",
2, "Ali",
3, "Mindorks");
Kotlin
val listOfNumber = listOf(1,
2,
3,
4)
val keyValue = mapOf(1 to
"Android",
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 here
return score;
}
Kotlin
fun getScore():
Int {
// logic here
return score
}
// as a single-expression function
fun getScore(): Int = score
无结束符号
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
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 way
object 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;
}
}
Kotlin
data class Developer(val name: String, val age: Int)
到此，关于“Kotlin与Java的异同点有哪些”的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注创新互联网站，小编会继续努力为大家带来更多实用的文章！
