Implementation of java interface to Kotlin class

Question

Scenario/Problem

In the below code example, I implemented IMessage from java to kotlin Message. But when I pass a value to message variable it says val cannot be reassigned

val message = Message()
message.user = Author()
message.text = ""
messate.createdAt = Date()
message.id = ""

public interface IMessage {
    String getId();
    String getText();
    IUser getUser();
    Date getCreatedAt();
}

class Message : IMessage {
    private var id: String = ""
    private var createdAt = Date()
    private var user = Author()
    private var text: String = ""

    override fun getId(): String {
        return id
    }

    override fun getCreatedAt(): Date {
        return createdAt
    }

    override fun getUser(): IUser {
        return user
    }

    override fun getText(): String {
        return text
    }

}

Question

What part of the code is wrong?

Expected Result

 val message = Message()
 message.id = ""
 message.text = ""
 message.user = Author()

Ganesh Tikone · Accepted Answer · 2018-09-11 07:05:05Z

2

Please change user object to IUser as I am not sure what it contains.

Interface

public interface IMessage {

    String getId();

    void setId(@NonNull String id);

    String getText();

    void setText(@NonNull String text);

    String getUser();

    void setUser(@NonNull String user);

    Date getCreatedAt();

    void setCreatedAt(@NonNull Date createdAt);
}

Message Class

class Message : IMessage {
    override fun setId(id: String) {
        this.id = id
    }

    override fun setText(text: String) {
        this.text = text
    }

    override fun setUser(user: String) {
        this.user = user
    }

    override fun setCreatedAt(createdAt: Date) {
        this.createdAt = createdAt
    }


    override fun getId(): String {
        return id
    }

    override fun getText(): String {
        return text
    }

    override fun getUser(): String {
        return user
    }

    override fun getCreatedAt(): Date {
        return createdAt
    }

    override fun toString(): String {
        return StringBuilder().append(id).append(user).append(text).append(createdAt.toString()).toString()
    }

    private var id: String = "id"
    private var createdAt: Date = Date()
    private var user: String = "user"
    private var text: String = "text"
}

MainActivity Code onCreate

        val message = Message()
        message.user = "Ganesh"
        message.createdAt = Date()
        message.id = "1"
        message.text = "Hello World"

        Log.e("First message object ", message.toString())

        message.user = "Tikone"
        message.createdAt = Date()
        message.id = "2"
        message.text = "Hello Kotlin"

        Log.e("After message object ", message.toString())

Result

09-11 12:30:40.188 29575-29575/com.sysanenet.myapplication E/First message object: 1GaneshHello WorldTue Sep 11 12:30:40 GMT+05:30 2018

09-11 12:30:40.188 29575-29575/com.sysanenet.myapplication E/After message object: 2TikoneHello KotlinTue Sep 11 12:30:40 GMT+05:30 2018

edited Sep 11, 2018 at 7:05

answered Sep 11, 2018 at 6:25

Ganesh Tikone

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4 Comments

ronscript Over a year ago

in this example, I'm still having Val cannot be reassigned var message = Message() message.user = Author() message.text = "" messate.createdAt = Date() message.id = ""

Ganesh Tikone Over a year ago

Please check, this is working. Interface implemented by your compiler was treating it as getter and setter method. In previous code we only had a getter. hence you can not access it with dot operator and change value.

ronscript Over a year ago

IMessage is from library, so I cannot change the current code

Ganesh Tikone Over a year ago

IMessage can be used for getting data from Message class. You can not set data to Message object then.

ronscript · Accepted Answer · 2018-09-11 06:25:01Z

In the below code is my answer, but I think I broke the rule of kotlin getter setter, because I created setter..

class Message : IMessage {
    private var id: String? = null
    private var text: String? = null
    private var user: IUser? = null
    private var createdAt: Date? = null

    fun setId(id: String) {
        this.id = id
    }

    fun setText(text: String) {
        this.text = text
    }

    fun setUser(user: IUser) {
        this.user = user
    }

    fun setCreatedAt(createdAt: Date) {
        this.createdAt = createdAt
    }

    override fun getId(): String? {
        return id
    }

    override fun getText(): String? {
        return text
    }

    override fun getUser(): IUser? {
        return user
    }

    override fun getCreatedAt(): Date? {
        return createdAt
    }

}

My Result

 val message = Message()
 message.setId("")
 message.setText("")
 message.setUser(Author())

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