大家好，我是光子郎，现如今，在Android开发中，Kotlin相信一直是大家的学习方向，那么今天，我将带大家看一看同样的JAVA代码用Kotlin应该怎么写吧，废话少说，开整！
目录
1.变量声明和初始化
JAVA:
String name = "John";
int age = 25;
kotlin:
val name: String = "John"
val age: Int = 25
2.可空类型
JAVA:
String nullableName = null;
Kotlin:
val nullableName: String? = null
3.函数定义
JAVA:
public void greet(String name) {
System.out.println("Hello, " + name + "!");
}
Kotlin:
fun greet(name: String) {
println("Hello, $name!")
}
4.字符串插值
JAVA:
String name = "John";
System.out.println("My name is " + name);
Kotlin:
val name = "John"
println("My name is $name")
5.条件语句
JAVA:
int number = 5;
if (number > 0) {
System.out.println("Positive");
} else if (number < 0) {
System.out.println("Negative");
} else {
System.out.println("Zero");
}
Kotlin:
val number = 5
when {
number > 0 -> println("Positive")
number < 0 -> println("Negative")
else -> println("Zero")
}
6.循环语句
JAVA:
for (int i = 0; i < 5; i++) {
System.out.println(i);
}
Kotlin:
for (i in 0 until 5) {
println(i)
}
7.列表初始化
JAVA:
List<String> names = new ArrayList<>();
names.add("John");
names.add("Alice");
Kotlin:
val names = listOf("John", "Alice")
8.列表遍历
JAVA:
List<String> names = Arrays.asList("John", "Alice");
for (String name : names) {
System.out.println(name);
}
Kotlin:
val names = listOf("John", "Alice")
for (name in names) {
println(name)
}
9.扩展函数
JAVA:
public static String capitalize(String input) {
return input.substring(0, 1).toUpperCase() + input.substring(1);
}
Kotlin:
fun String.capitalize(): String {
return this.substring(0, 1).toUpperCase() + this.substring(1)
}
10.空安全调用
JAVA:
String nullableName = null;
int length = nullableName != null ? nullableName.length() : 0;
Kotlin:
val nullableName: String? = null
val length = nullableName?.length ?: 0
11.对象实例化
JAVA:
MyClass myClass = new MyClass();
Kotlin:
val myClass = MyClass()
12.静态方法调用
JAVA:
int result = Math.max(5, 10);
Kotlin:
val result = max(5, 10)
13.默认参数值
JAVA:
public void greet(String name, String message) {
System.out.println("Hello, " + name + "! " + message);
}
public void greet(String name) {
greet(name, "Welcome!");
}
Kotlin:
fun greet(name: String, message: String = "Welcome!") {
println("Hello, $name! $message")
}
14.可变参数
JAVA:
public void printNumbers(int... numbers) {
for (int number : numbers) {
System.out.println(number);
}
}
Kotlin:
fun printNumbers(vararg numbers: Int) {
for (number in numbers) {
println(number)
}
}
15.数据类
JAVA:
public class Person {
private String name;
private int age;
// Constructors, getters, setters, toString
}
Kotlin:
data class Person(val name: String, val age: Int)
16.扩展属性
Kotlin:
val String.firstChar: Char
get() = this[0]
17.Lambda表达式
JAVA:
Runnable runnable = () -> System.out.println("Hello");
Kotlin:
val runnable: Runnable = { println("Hello") }
18.过滤列表
JAVA:
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> evenNumbers = new ArrayList<>();
for (Integer number : numbers) {
if (number % 2 == 0) {
evenNumbers.add(number);
}
}
Kotlin:
val numbers = listOf(1, 2, 3, 4, 5)
val evenNumbers = numbers.filter { it % 2 == 0 }
19.使用扩展函数过滤列表
JAVA:
List<String> names = Arrays.asList("John", "Alice", "Bob");
List<String> filteredNames = new ArrayList<>();
for (String name : names) {
if (name.length() > 4) {
filteredNames.add(name);
}
}
Kotlin:
val names = listOf("John", "Alice", "Bob")
val filteredNames = names.filter { it.length > 4 }
20.使用Stream操作过滤列表
JAVA:
List<String> names = Arrays.asList("John", "Alice", "Bob");
List<String> filteredNames = names.stream()
.filter(name -> name.length() > 4)
.collect(Collectors.toList());
Kotlin:
val names = listOf("John", "Alice", "Bob")
val filteredNames = names.filter { it.length > 4 }
21.使用map操作变换列表元素
JAVA:
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> squaredNumbers = new ArrayList<>();
for (Integer number : numbers) {
squaredNumbers.add(number * number);
}
Kotlin:
val numbers = listOf(1, 2, 3, 4, 5)
val squaredNumbers = numbers.map { it * it }
22.使用Map集合
JAVA:
Map<String, Integer> ages = new HashMap<>();
ages.put("John", 25);
ages.put("
Kotlin:
val ages = mapOf("John" to 25, "Alice" to 30)
23.使用函数引用
JAVA:
List<String> names = Arrays.asList("John", "Alice", "Bob");
names.forEach(System.out::println);
Kotlin:
val names = listOf("John", "Alice", "Bob")
names.forEach(::println)
24.使用委托类实现接口
JAVA:
public class MyListener implements OnClickListener {
@Override
public void onClick(View view) {
// Handle click event
}
}
Kotlin:
class MyListener : OnClickListener {
override fun onClick(view: View) {
// Handle click event
}
}
25.使用Lambda表达式实现接口
JAVA:
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
// Handle click event
}
});
Kotlin:
button.setOnClickListener { view ->
// Handle click event
}
26.使用lateinit修饰符
Kotlin:
lateinit var name: String
27.使用协程进行异步操作
Kotlin:
viewModelScope.launch {
val result = async { fetchData() }
val data = result.await()
// Process data
}
28.使用对象表达式创建匿名类
JAVA:
Runnable runnable = new Runnable() {
@Override
public void run() {
// Run code
}
};
Kotlin:
val runnable = object : Runnable {
override fun run() {
// Run code
}
}
29.使用委托属性
Kotlin:
val lazyValue: String by lazy {
// Compute the value
"Hello"
}
30.使用companion object创建静态成员
JAVA:
public class MyClass {
public static final String NAME = "John";
}
Kotlin:
class MyClass {
companion object {
const val NAME = "John"
}
}
31.使用安全调用操作符
JAVA:
String nullableName = null;
int length = nullableName != null ? nullableName.length() : 0;
Kotlin:
val nullableName: String? = null
val length = nullableName?.length ?: 0
32.使用 Elvis 操作符
JAVA:
String nullableName = null;
String nonNullableName = nullableName != null ? nullableName : "Unknown";
Kotlin:
val nullableName: String? = null
val nonNullableName = nullableName ?: "Unknown"
33.使用区间
JAVA:
for (int i = 0; i <= 10; i++) {
System.out.println(i);
}
Kotlin:
for (i in 0..10) {
println(i)
}
34.使用区间并指定步长
JAVA:
for (int i = 0; i <= 10; i += 2) {
System.out.println(i);
}
Kotlin:
for (i in 0..10 step 2) {
println(i)
}
35.使用区间反向迭代
JAVA:
for (int i = 10; i >= 0; i--) {
System.out.println(i);
}
Kotlin:
for (i in 10 downTo 0) {
println(i)
}
36.使用条件表达式
JAVA:
int a = 5;
int b = 10;
int max = a > b ? a : b;
Kotlin:
val a = 5
val b = 10
val max = if (a > b) a else b
37.使用类型推断
JAVA:
List<String> names = new ArrayList<>();
Kotlin:
val names = mutableListOf<String>()
38.使用标签和跳转
JAVA:
outerLoop: for (int i = 0; i < 5; i++) {
for (int j = 0; j < 5; j++) {
if (j == 3) {
break outerLoop;
}
System.out.println("i: " + i + ", j: " + j);
}
}
Kotlin:
outerLoop@ for (i in 0 until 5) {
for (j in 0 until 5) {
if (j == 3) {
break@outerLoop
}
println("i: $i, j: $j")
}
}
39.使用标准库函数
JAVA:
List<String> names = Arrays.asList("John", "Alice", "Bob");
List<String> upperCaseNames = new ArrayList<>();
for (String name : names) {
upperCaseNames.add(name.toUpperCase());
}
Kotlin:
val names = listOf("John", "Alice", "Bob")
val upperCaseNames = names.map { it.toUpperCase() }
40.使用顶层函数
JAVA:
public class Utils {
public static int add(int a, int b) {
return a + b;
}
}
Kotlin:
fun add(a: Int, b: Int): Int {
return a + b
}
41.使用单例对象
JAVA:
public class MySingleton {
private static MySingleton instance;
private MySingleton() {
// Private constructor
}
public static MySingleton getInstance() {
if (instance == null) {
instance = new MySingleton();
}
return instance;
}
}
Kotlin:
object MySingleton {
// Single instance
}
42.使用函数类型和高阶函数
JAVA:
public interface MyListener {
void onClick(View view);
}
public class Button {
private MyListener listener;
public void setOnClickListener(MyListener listener) {
this.listener = listener;
}
public void click() {
if (listener != null) {
listener.onClick(this);
}
}
}
Kotlin:
typealias MyListener = (view: View) -> Unit
class Button {
private var listener: MyListener? = null
fun setOnClickListener(listener: MyListener) {
this.listener = listener
}
fun click() {
listener?.invoke(this)
}
}
43.使用委托类实现属性
JAVA:
public class MyDelegate {
private String value;
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
public class MyClass {
private MyDelegate delegate = new MyDelegate();
public String getValue() {
return delegate.getValue();
}
public void setValue(String value) {
delegate.setValue(value);
}
}
Kotlin:
class MyDelegate {
var value: String by Delegates.observable("") { _, old, new ->
// Handle value changes
}
}
class MyClass {
private val delegate = MyDelegate()
var value: String
get() = delegate.value
set(value) {
delegate.value = value
}
}
44.使用扩展函数操作集合
JAVA:
List<String> names = Arrays.asList("John", "Alice", "Bob");
List<String> uppercaseNames = new ArrayList<>();
for (String name : names) {
uppercaseNames.add(name.toUpperCase());
}
Kotlin:
val names = listOf("John", "Alice", "Bob")
val uppercaseNames = names.map { it.toUpperCase() }
45.使用Lambda表达式过滤集合
JAVA:
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> evenNumbers = new ArrayList<>();
for (Integer number : numbers) {
if (number % 2 == 0) {
evenNumbers.add(number);
}
}
Kotlin:
val numbers = listOf(1, 2, 3, 4, 5)
val evenNumbers = numbers.filter { it % 2 == 0 }
46.使用集合函数操作集合
JAVA:
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
int sum = 0;
for (Integer number : numbers) {
sum += number;
}
Kotlin:
val numbers = listOf(1, 2, 3, 4, 5)
val sum = numbers.sum()
47.使用with函数简化代码块
JAVA:
StringBuilder builder = new StringBuilder();
builder.append("Hello");
builder.append(" ");
builder.append("World");
String result = builder.toString();
Kotlin:
val result = with(StringBuilder()) {
append("Hello")
append(" ")
append("World")
toString()
}
48.使用apply函数初始化对象
JAVA:
Person person = new Person();
person.setName("John");
person.setAge(25);
Kotlin:
val person = Person().apply {
name = "John"
age = 25
}
49.使用run函数执行可为空的代码块
JAVA:
String nullableName = null;
int length = 0;
if (nullableName != null) {
length = nullableName.length();
}
Kotlin:
val nullableName: String? = null
val length = nullableName?.run { length } ?: 0
50.使用use函数自动关闭资源
JAVA:
InputStream inputStream = new FileInputStream("file.txt");
try {
// Read from the input stream
} finally {
if (inputStream != null) {
inputStream.close();
}
}
Kotlin:
val inputStream = FileInputStream("file.txt")
inputStream.use {
// Read from the input stream
}
以上就是Android开发中JAVA代码写法与kotlin的区别，希望能够帮助大家在开发过程中提高kotlin开发的效率~
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