from java to kotlin
1.0.0
จาก Java ถึง Kotlin - เอกสารโกงของคุณสำหรับ Java ถึง Kotlin
สวัสดี ฉันชื่อ Amit Shekhar ผู้ร่วมก่อตั้ง @ Outcome School • IIT 2010-14 • ฉันได้สอนและให้คำปรึกษานักพัฒนาจำนวนมาก และความพยายามของพวกเขาทำให้พวกเขาได้งานด้านเทคโนโลยีที่มีรายได้สูง ช่วยบริษัทเทคโนโลยีหลายแห่งในการแก้ปัญหาเฉพาะตัวของพวกเขา และสร้าง ห้องสมุดโอเพ่นซอร์สจำนวนมากถูกใช้โดยบริษัทชั้นนำ ฉันหลงใหลในการแบ่งปันความรู้ผ่านโอเพ่นซอร์ส บล็อก และวิดีโอ
คุณสามารถเชื่อมต่อกับฉันได้ที่:
ชวา
System . out . print ( "Amit Shekhar" );
System . out . println ( "Amit Shekhar" );คอตลิน
print ( " Amit Shekhar " )
println ( " Amit Shekhar " )ชวา
String name = "Amit Shekhar" ;
final String name = "Amit Shekhar" ;คอตลิน
var name = " Amit Shekhar "
val name = " Amit Shekhar " ชวา
String otherName ;
otherName = null ;คอตลิน
var otherName : String?
otherName = null ชวา
if ( text != null ) {
int length = text . length ();
}คอตลิน
text?. let {
val length = text.length
}
// or simply
val length = text?.lengthชวา
String sampleString = "Shekhar" ;
if (! sampleString . isEmpty ()) {
myTextView . setText ( sampleString );
}
if ( sampleString != null && ! sampleString . isEmpty ()){
myTextView . setText ( sampleString );
}คอตลิน
var sampleString = " Shekhar "
if (sampleString.isNotEmpty()){ // the feature of kotlin extension function
myTextView.text = sampleString
}
if ( ! sampleString.isNullOrEmpty()){
myTextView.text = sampleString
}ชวา
String firstName = "Amit" ;
String lastName = "Shekhar" ;
String message = "My name is: " + firstName + " " + lastName ;คอตลิน
var firstName = " Amit "
var lastName = " Shekhar "
var message = " My name is: $firstName $lastName " ชวา
String text = "First Line n " +
"Second Line n " +
"Third Line" ;คอตลิน
val text = """
|First Line
|Second Line
|Third Line
""" .trimMargin()ชวา
String str = "Java to Kotlin Guide" ;
String substr = "" ;
//print java
substr = str . substring ( 0 , 4 );
System . out . println ( "substring = " + substr );
//print kotlin
substr = str . substring ( 8 , 14 );
System . out . println ( "substring = " + substr );คอตลิน
var str = " Java to Kotlin Guide "
var substr = " "
// print java
substr = str.substring( 0 .. 3 ) //
println ( " substring $substr " )
// print kotlin
substr = str.substring( 8 .. 13 )
println ( " substring $substr " )ชวา
String text = x > 5 ? "x > 5" : "x <= 5" ;
String message = null ;
log ( message != null ? message : "" );คอตลิน
val text = if (x > 5 ) " x > 5 " else " x <= 5 "
val message : String? = null
log(message ? : " " )ชวา
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 ;คอตลิน
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 ชวา
if ( object instanceof Car ) {
Car car = ( Car ) object ;
}คอตลิน
if ( object is Car) {
var car = object as Car
}
// if object is null
var car = object as ? Car // var car = object as Car?ชวา
if ( object instanceof Car ) {
Car car = ( Car ) object ;
}คอตลิน
if ( object is Car) {
var car = object // smart casting
}
// if object is null
if ( object is Car?) {
var car = object // smart casting, car will be null
}ชวา
if ( score >= 0 && score <= 300 ) { }คอตลิน
if (score in 0 .. 300 ) { }ชวา
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" ;
}คอตลิน
var score = // some score
var grade = when (score) {
9 , 10 -> " Excellent "
in 6 .. 8 -> " Good "
4 , 5 -> " OK "
else -> " Fail "
}ชวา
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 ()) { }คอตลิน
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) { }ชวา
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 , "Anand" );
map . put ( 3 , "Messi" );
// Java 9
final List < Integer > listOfNumber = List . of ( 1 , 2 , 3 , 4 );
final Map < Integer , String > keyValue = Map . of ( 1 , "Amit" ,
2 , "Anand" ,
3 , "Messi" );คอตลิน
val listOfNumber = listOf ( 1 , 2 , 3 , 4 )
val keyValue = mapOf ( 1 to " Amit " ,
2 to " Anand " ,
3 to " Messi " )ชวา
// 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 ));
cars . parallelStream (). filter ( car -> car . speed > 100 ). forEach ( car -> System . out . println ( car . speed ));คอตลิน
cars.forEach {
println (it.speed)
}
cars.filter { it.speed > 100 }
.forEach { println (it.speed)}
// kotlin 1.1+
cars.stream().filter { it.speed > 100 }.forEach { println (it.speed)}
cars.parallelStream().filter { it.speed > 100 }.forEach { println (it.speed)}ชวา
String [] splits = "param=car" . split ( "=" );
String param = splits [ 0 ];
String value = splits [ 1 ];คอตลิน
val (param, value) = " param=car " .split( " = " )ชวา
void doSomething () {
// logic here
}คอตลิน
fun doSomething () {
// logic here
}ชวา
double calculateCost ( int quantity , double pricePerItem ) {
return pricePerItem * quantity ;
}
double calculateCost ( int quantity ) {
// default price is 20.5
return 20.5 * quantity ;
}คอตลิน
fun calculateCost ( quantity : Int , pricePerItem : Double = 20.5) = quantity * pricePerItem
calculateCost( 10 , 25.0 ) // 250
calculateCost( 10 ) // 205
ชวา
void doSomething ( int ... numbers ) {
// logic here
}คอตลิน
fun doSomething ( vararg numbers : Int ) {
// logic here
}ชวา
int getScore () {
// logic here
return score ;
}คอตลิน
fun getScore (): Int {
// logic here
return score
}
// as a single-expression function
fun getScore (): Int = score
// even simpler (type will be determined automatically)
fun getScore () = score // return-type is Int ชวา
int getScore ( int value ) {
// logic here
return 2 * value ;
}คอตลิน
fun getScore ( value : Int ): Int {
// logic here
return 2 * value
}
// as a single-expression function
fun getScore ( value : Int ): Int = 2 * value
// even simpler (type will be determined automatically)
fun getScore ( value : Int ) = 2 * value // return-type is int ชวา
public class Utils {
private Utils () {
// This utility class is not publicly instantiable
}
public static int getScore ( int value ) {
return 2 * value ;
}
}คอตลิน
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
}
}ชวา
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 +
'}' ;
}
}คอตลิน
data class Developer ( var name : String , var age : Int )
ชวา
public class Developer implements Cloneable {
private String name ;
private int age ;
public Developer ( String name , int age ) {
this . name = name ;
this . age = age ;
}
@ Override
protected Object clone () throws CloneNotSupportedException {
return ( Developer ) super . clone ();
}
}
// cloning or copying
Developer dev = new Developer ( "Messi" , 30 );
try {
Developer dev2 = ( Developer ) dev . clone ();
} catch ( CloneNotSupportedException e ) {
// handle exception
}คอตลิน
data class Developer ( var name : String , var age : Int )
// cloning or copying
val dev = Developer ( " Messi " , 30 )
val dev2 = dev.copy()
// in case you only want to copy selected properties
val dev2 = dev.copy(age = 25 )
ชวา
// Example #1
interface SomeInterface < T > {
void doSomething ( T data );
}
class SomeClass implements SomeInterface < String > {
@ Override
public void doSomething ( String data ) {
// some logic
}
}
// Example #2
interface SomeInterface < T extends Collection <?>> {
void doSomething ( T data );
}
class SomeClass implements SomeInterface < List < String >> {
@ Override
public void doSomething ( List < String > data ) {
// some logic
}
}คอตลิน
interface SomeInterface < T > {
fun doSomething ( data : T )
}
class SomeClass : SomeInterface < String > {
override fun doSomething ( data : String ) {
// some logic
}
}
interface SomeInterface < T : Collection < * >> {
fun doSomething ( data : T )
}
class SomeClass : SomeInterface < List < String >> {
override fun doSomething ( data : List < String >) {
// some logic
}
}ชวา
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 );คอตลิน
fun Int. triple (): Int {
return this * 3
}
var result = 3 .triple()ชวา
Person person ;คอตลิน
internal lateinit var person : Person ชวา
public enum Direction {
NORTH ( 1 ),
SOUTH ( 2 ),
WEST ( 3 ),
EAST ( 4 );
int direction ;
Direction ( int direction ) {
this . direction = direction ;
}
public int getDirection () {
return direction ;
}
}คอตลิน
enum class Direction ( val direction : Int ) {
NORTH ( 1 ),
SOUTH ( 2 ),
WEST ( 3 ),
EAST ( 4 );
}ชวา
List < Profile > profiles = loadProfiles ( context );
Collections . sort ( profiles , new Comparator < Profile >() {
@ Override
public int compare ( Profile profile1 , Profile profile2 ) {
if ( profile1 . getAge () > profile2 . getAge ()) return 1 ;
if ( profile1 . getAge () < profile2 . getAge ()) return - 1 ;
return 0 ;
}
});คอตลิน
val profile = loadProfiles(context)
profile.sortedWith( Comparator ({ profile1, profile2 ->
if (profile1.age > profile2.age) return @Comparator 1
if (profile1.age < profile2.age) return @Comparator - 1
return @Comparator 0
}))ชวา
AsyncTask < Void , Void , Profile > task = new AsyncTask < Void , Void , Profile >() {
@ Override
protected Profile doInBackground ( Void ... voids ) {
// fetch profile from API or DB
return null ;
}
@ Override
protected void onPreExecute () {
super . onPreExecute ();
// do something
}
};คอตลิน
val task = object : AsyncTask < Void , Void , Profile >() {
override fun doInBackground ( vararg voids : Void ): Profile ? {
// fetch profile from API or DB
return null
}
override fun onPreExecute () {
super .onPreExecute()
// do something
}
}ชวา
public class User {
{ //Initialization block
System . out . println ( "Init block" );
}
}คอตลิน
class User {
init { // Initialization block
println ( " Init block " )
}
} Copyright (C) 2024 Amit Shekhar
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
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