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Java和Kotlin有哪些区别代码实例展示

时间:2017-05-31 13:15来源:知行网www.zhixing123.cn 编辑:麦田守望者

自从谷歌 I/O 2017宣布将支持 Kotlin 作为 Android 开发的 First-Class 语言,相信各位程序员的朋友圈都被Kotlin的消息轰炸了吧,支持Java的“守旧派”认为Java将稳坐霸主地位不动摇,支持Kotlin的“维新派”认为Kotlin很可能会把Java拉下马。其实,笔者认为新语言的出现对于程序员来说并不是一件新鲜事儿,程序员始终践行着“活到老,学到老”,真正能够对程序员产生影响的新语言的使用和性能。

GitHub 用户amitshekhariitbhu在GitHub上贴图分享了Java和Kotlin的语法区别,下面我们就一起来看一下吧!

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) {
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
}

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标签(Tag):Java Kotlin
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