Conversion Java to Kotlin

In this tutorial you will learn about the Conversion Java to Kotlin and its application with practical example.

Intent & Conversion from Java to Kotlin

Table Of Contents−

Intent: As we know that intent is used to redirect one activity to another activity.Intent Facilitate communication between components, It is Used to invoke components. Uses of Intent are: Starting an Activity, Starting a Service ,Delivering a Broadcast etc.
Types of Intent : Explicit Intents, Implicit Intents .
It is briefly discussed in Android tutorial, Please check Android tutorial for more details.

Android studio version 3.0 provide us facilities to convert our Java class to Kotlin class by following some easy steps. Lets see these steps.

Example: With this given example we get understand about conversion and Also we will learn use of Intent in Android with Kotlin. Follow below steps for Conversion.

Step 1^st: In below screen I wrote code of activity in java which we used to do before Kotlin.

Step 2^nd :Click on “Code” option in menu of Android Studio and go to “Convert Java File to Kotlin File” or simply use shortcut press “Ctrl+Alt+Shift+K” for converting Java file to Kotlin file. Like below Image.

# After Pressing this option it will be doing process for converting Java File to Kotlin.

Step 3^rd: In step third the Java file is converted to Kotlin File, Just check below image.

So this was Java file to Kotlin file conversion. I have used two Activities here , First One is MainActivity and Second one is SecondActivity (Converted file).

#MainActivity.kt: The below code is used for Main Activity.

package com.w3adda.helloapp

import android.content.Intent
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.android.synthetic.main.header.*

class MainActivity : AppCompatActivity() {


    override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
this.heading.setText("Main Activity")
this.btn_fir.setOnClickListener {
val i = Intent(this, SecondActivity::class.java)
            startActivity(i)
        }
    }
}

package com.w3adda.helloapp

import android.content.Intent

import android.support.v7.app.AppCompatActivity

import android.os.Bundle

import android.widget.Button

import kotlinx.android.synthetic.main.activity_main.*

import kotlinx.android.synthetic.main.header.*

class MainActivity : AppCompatActivity() {

override fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState)

setContentView(R.layout.activity_main)

this.heading.setText("Main Activity")

this.btn_fir.setOnClickListener {

val i = Intent(this, SecondActivity::class.java)

startActivity(i)

}

#SecondActivity.java:The below code is used for Second Activity(Before Conversion).

package com.infowind.myapplication;


import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;


public class SecondActivity extends AppCompatActivity {

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        Button btn_next=(Button)findViewById(R.id.btn_next);
        btn_next.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
                Intent i =new Intent(SecondActivity.this,MainActivity.class);
                startActivity(i);
            }
        });
    }
}

package com.infowind.myapplication;

import android.content.Intent;

import android.os.Bundle;

import android.support.annotation.Nullable;

import android.support.v7.app.AppCompatActivity;

import android.view.View;

import android.widget.Button;

public class SecondActivity extends AppCompatActivity {

@Override

protected void onCreate(@Nullable Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_second);

Button btn_next=(Button)findViewById(R.id.btn_next);

btn_next.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

Intent i =new Intent(SecondActivity.this,MainActivity.class);

startActivity(i);

}

});

}

SecondActivity.kt: After conversion of java file to Kotlin file will look like below code.

package com.w3adda.helloapp

import android.content.Intent
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import kotlinx.android.synthetic.main.activity_second.*
import kotlinx.android.synthetic.main.header.*

class SecondActivity : AppCompatActivity() {


    override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_second)
val btn_next=findViewById<View>(R.id.btn_next) as Button
btn_next.setOnClickListener {
val i = Intent(this, MainActivity::class.java)
            startActivity(i)
        }
    }
}

package com.w3adda.helloapp

import android.content.Intent

import android.support.v7.app.AppCompatActivity

import android.os.Bundle

import android.widget.Button

import kotlinx.android.synthetic.main.activity_second.*

import kotlinx.android.synthetic.main.header.*

class SecondActivity : AppCompatActivity() {

override fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState)

setContentView(R.layout.activity_second)

val btn_next=findViewById<View>(R.id.btn_next) as Button

btn_next.setOnClickListener {

val i = Intent(this, MainActivity::class.java)

startActivity(i)

}

XML: There are three XML files are used in this project 1^st is for Main Activity, 2^nd is for Second Activity and 3^rd is “Header” File which is used in both XML. Checkout all below.

#header.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:background="@color/header"
android:layout_height="50dp">
<TextView
android:layout_width="wrap_content"
android:layout_height="40dp"
android:text="Main Activity"
android:textSize="18sp"
android:layout_margin="10dp"
android:id="@+id/heading"

/>

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:background="@color/header"

android:layout_height="50dp">

<TextView

android:layout_width="wrap_content"

android:layout_height="40dp"

android:text="Main Activity"

android:textSize="18sp"

android:layout_margin="10dp"

android:id="@+id/heading"

</RelativeLayout>

#activity_main:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.w3adda.helloapp.MainActivity">

<include layout="@layout/header"
android:id="@+id/heder"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/tv_hello"
android:textColor="#000"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"

/>

<Button
android:id="@+id/btn_fir"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Click"
android:layout_above="@+id/tv_hello"
android:layout_centerHorizontal="true"
android:layout_marginBottom="10dp"/>

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

tools:context="com.w3adda.helloapp.MainActivity">

<include layout="@layout/header"

android:id="@+id/heder"/>

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:id="@+id/tv_hello"

android:textColor="#000"

android:layout_centerHorizontal="true"

android:layout_centerVertical="true"

<Button

android:id="@+id/btn_fir"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Click"

android:layout_above="@+id/tv_hello"

android:layout_centerHorizontal="true"

android:layout_marginBottom="10dp"/>

</RelativeLayout>

#activity_second:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.w3adda.helloapp.SecondActivity">
<include layout="@layout/header"
android:id="@+id/header"/>


<Button
android:id="@+id/btn_next"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="107dp"
android:text="Next" />
</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

tools:context="com.w3adda.helloapp.SecondActivity">

<include layout="@layout/header"

android:id="@+id/header"/>

<Button

android:id="@+id/btn_next"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentTop="true"

android:layout_centerHorizontal="true"

android:layout_marginTop="107dp"

android:text="Next" />

</RelativeLayout>

So we are all set for this code. Guys do not forget to declare Second Activity in “Manifest.xml” file.

Run: Follow all steps and after completion Run your project, you will get Output like below images.

Hopefully this will help you to get conversion of Java file to Kotlin file and also Intent in Kotlin.

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