以下是一个Kotlin版Android程序的小例子

先在build.gradle文件中添加布局拓展，可以在java文件中直接使用在布局文件中声明的id的控件，省去findViewById的步骤。

apply plugin: 'kotlin-android-extensions'

再在build.gradle中的dependencies中添加anko，可以直接在java文件中写布局，省去xml文件。

compile "org.jetbrains.anko:anko-sdk15:0.9.1"

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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="linchange.example.com.kotlin_android2.MainActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <TextView
        android:id="@+id/tv2"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="TextView"
        android:gravity="center" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        app:srcCompat="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>

MainActivity.java

package linchange.example.com.kotlin_android2

import android.os.Bundle
import android.support.design.widget.Snackbar
import android.support.v7.app.AppCompatActivity
import android.view.Menu
import android.view.MenuItem
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.android.synthetic.main.content_main.*
import org.jetbrains.anko.onClick
import org.jetbrains.anko.startActivity

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(toolbar)

        fab.onClick { view -> //为浮动按钮设置点击事件
            Snackbar.make(view!!, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show()
            tv.text = "${System.currentTimeMillis()}" //设置textView的文本内容为当前时间

            //跳转页面，泛型为需要跳转的页面，圆括号中的键值对为所需放入的Extras
            startActivity<Main2Activity>("Key" to "from The Great Wall")
        }
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        menuInflater.inflate(R.menu.menu_main, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        val id = item.itemId

        if (id == R.id.action_settings) {
            return true
        }

        return super.onOptionsItemSelected(item)
    }
}

Main2Activity.java

package linchange.example.com.kotlin_android2

import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.text.Editable
import android.text.TextWatcher
import android.view.Gravity
import android.widget.Toast
import org.jetbrains.anko.relativeLayout
import org.jetbrains.anko.textView
import org.jetbrains.anko.wrapContent

class Main2Activity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        relativeLayout { //相对布局
            textView(intent.extras["Key"]?.toString() ?: "Nothing") { //设置textView的文字
                addTextChangedListener(object : TextWatcher { //匿名对象调用接口
                    override fun afterTextChanged(s: Editable?) {
                        Toast.makeText(this@Main2Activity, "textView Change", 
                            Toast.LENGTH_SHORT).show()
                    }

                    override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
                    }

                    override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
                    }
                })
            }.lparams(wrapContent, wrapContent) { //设置textView的布局参数
                gravity = Gravity.CENTER
            }
        }

    }
}

MainActivity视图

Main2Activity视图