Java issue

activity main.xml


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:background="#ffffff"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:weightSum="1"
    tools:context="com.example.android.rareenglishwords.MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_weight="0.02"
        android:text="Chinatown is a country." />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="0.19"
        android:orientation="horizontal"
        android:weightSum="1">

        <Button
            android:id="@+id/yesButton"
            android:layout_width="wrap_content"
            android:layout_height="55dp"
            android:layout_gravity="center_vertical"
            android:layout_weight="0.11"
            android:text="Yes" />

        <Button
            android:id="@+id/noButton"
            android:layout_width="wrap_content"
            android:layout_height="57dp"
            android:layout_gravity="center_vertical"
            android:layout_weight="0.23"
            android:text="No" />

    </LinearLayout>
</LinearLayout>





Main xml



package com.example.android.rareenglishwords;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    public Button yesButton;
    public Button noButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        yesButton = (Button) findViewById(R.id.yesButton);
        noButton = (Button) findViewById(R.id.noButton);

        yesButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //Does nothing yet but sonn
                Toast.makeText(MainActivity.this,
                        R.string.incorrect_toast,
                        Toast.LENGTH_SHORT).show();
            }
        });

        noButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //Does nothing yet but sonn
                Toast.makeText(MainActivity.this,
                        R.string.correct_toast,
                        Toast.LENGTH_SHORT).show();
            }
        });


    }
}