Kotlin 带你飞 • 语法篇 • 类


本文采用与 Java 语法作对比的方式罗列并介绍 Kotlin 类的用法。依然是类似《Kotlin 带你飞 • 语法篇 • 基础》的套路,希望能对看到这篇文章的您有所帮助吧。

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Constructor Call

Java

final File file = new File("file.txt");

Kotlin

val file = File("file.txt")

Class

Java

public final class User {  }

Kotlin

class User

Open Class

Java

public class User {  }

Kotlin

open class User

Final Attributes

Java

final class User {
	private final String name;

	public User(String name) {
		this.name = name;
	}
	public String getName() {
		return name;
	}
}

Kotlin

class User(val name: String)

Primary Constructor

Java

final class User {
	private String name;

	public User(String name) {
		this.name = name;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

Kotlin

class User(var name: String)

Optional Arguments in Constructors

Java

final class User {
     private String name;
     private String lastName;

     public User(String name) {
         this(name, "");
     }
     public User(String name, String lastName) {
         this.name = name;
         this.lastName = lastName;
     }
     // And Getters & Setters
 }

Kotlin

class User(var name: String, var lastName: String = "")

##Properties

Java

public class Document {
	private String id = "00x";

	public String getId() {
		return id;
	}
	public void setId(String id) {
		if(id != null && !id.isEmpty()) {
			this.id = id;
		}
	}
}

Kotlin

class Document{
	var id : String = "00x"
		set(value) {
			if(value.isNotEmpty())  field = value
		}
}

Abstract Class

Java

public abstract class Document{
   public abstract int calculateSize();
}

public class Photo extends Document{
    @Override
    public int calculateSize() {

    }
}

Kotlin

abstract class Document {
    abstract fun calculateSize(): Int
}

class Photo : Document() {
    override fun calculateSize(): Int {

    }
}

Singleton

Java

public class Document {
	private static final Document INSTANCE = new Document();

	public static Document getInstance(){
	   return INSTANCE;
	}
}

Kotlin

object Document {

}

Extensions

Java

public class ByteArrayUtils {
	public static String toHexString(byte[] data) {

	}
}

final byte[] dummyData = new byte[10];
final String hexValue = ByteArrayUtils.toHexString(dummyData);

Kotlin

fun ByteArray.toHex() : String {

}

val dummyData = byteArrayOf()
val hexValue = dummyData.toHex()

Inner Class

Java

public class Documment {
    class InnerClass {

    }
}

Kotlin

class Document {
    inner class InnerClass
}

Nested Class

Java

public class Documment {
    public static class InnerClass {

    }
}

Kotlin

class Document {
    class InnerClass
}

Interface

Java

public interface Printable {
    void print();
}

public class Document implements Printable {
    @Override
    public void print() {

    }
}

Kotlin

interface Printable{
    fun print()
}

class Document : Printable {
    override fun print() {

    }
}

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