activity_main.xml

<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"
    android:background="@drawable/bk_grass"
    tools:context="com.yojiokisoft.whacmole.app.MainActivity">

    <LinearLayout
        android:id="@+id/relativeLayout"
        android:layout_width="fill_parent"
        android:orientation="horizontal"
        android:paddingTop="20dp"
        android:paddingLeft="10dp"
        android:layout_height="60dp">

        <TextView
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Score:"
            android:textSize="25sp" />

        <TextView
            android:id="@+id/scoreText"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="100"
            android:textSize="30sp" />

        <TextView
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Time:"
            android:textSize="25sp" />

        <TextView
            android:id="@+id/timeText"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="60"
            android:textSize="30sp" />

    </LinearLayout>

    <FrameLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_alignParentEnd="true"
        android:layout_alignParentRight="false"
        android:layout_below="@+id/relativeLayout">

        <TableLayout
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_alignParentLeft="true"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true">

            <TableRow
                android:layout_width="fill_parent"
                android:layout_height="fill_parent">

                <Button
                    android:id="@+id/Button1A"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button1B"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button1C"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button1D"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

            </TableRow>

            <TableRow
                android:layout_width="fill_parent"
                android:layout_height="fill_parent">

                <Button
                    android:id="@+id/Button2A"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button2B"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button2C"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button2D"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

            </TableRow>

            <TableRow
                android:layout_width="fill_parent"
                android:layout_height="fill_parent">

                <Button
                    android:id="@+id/Button3A"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button3B"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button3C"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button3D"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

            </TableRow>

            <TableRow
                android:layout_width="fill_parent"
                android:layout_height="fill_parent">

                <Button
                    android:id="@+id/Button4A"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button4B"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button4C"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button4D"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

            </TableRow>

            <TableRow
                android:layout_width="fill_parent"
                android:layout_height="fill_parent">

                <Button
                    android:id="@+id/Button5A"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button5B"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button5C"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

                <Button
                    android:id="@+id/Button5D"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:background="@drawable/bg_button" />

            </TableRow>
        </TableLayout>

        <RelativeLayout
            android:id="@+id/game_over_container"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical"
            android:background="#8000"
            android:clickable="true"
            android:visibility="invisible">

            <TextView
                android:id="@+id/game_over_text"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_centerInParent="true"
                android:text="Game Over"
                android:textSize="50sp"
                android:textColor="#ffffff"/>

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_below="@+id/game_over_text"
                android:layout_centerHorizontal="true"
                android:text="画面タップでリプレイ"
                android:textSize="20sp"
                android:textColor="#888888"/>

        </RelativeLayout>
    </FrameLayout>

</RelativeLayout>

MainActivity.java

package com.yojiokisoft.whacmole.app;

import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.widget.TextView;

import java.util.Timer;
import java.util.TimerTask;


public class MainActivity extends ActionBarActivity {
    private Button[][] mButton = new Button[5][4]; // [行][列]
    private Button mMoleButton;
    private TextView mScoreText;
    private int mScore;
    private TextView mTimeText;
    private int mGameTime = 60;
    private Timer mTimer = null;
    private Handler mHandler = new Handler();
    private RelativeLayout mGameOver;

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

        mMoleButton = null;
        mScore = 0;
        mScoreText = (TextView) findViewById(R.id.scoreText);
        mTimeText = (TextView) findViewById(R.id.timeText);
        mGameOver = (RelativeLayout) findViewById(R.id.game_over_container);
        mGameOver.setOnClickListener(mGameOverClicked);

        mButton[0][0] = (Button) findViewById(R.id.Button1A);
        mButton[0][1] = (Button) findViewById(R.id.Button1B);
        mButton[0][2] = (Button) findViewById(R.id.Button1C);
        mButton[0][3] = (Button) findViewById(R.id.Button1D);

        mButton[1][0] = (Button) findViewById(R.id.Button2A);
        mButton[1][1] = (Button) findViewById(R.id.Button2B);
        mButton[1][2] = (Button) findViewById(R.id.Button2C);
        mButton[1][3] = (Button) findViewById(R.id.Button2D);

        mButton[2][0] = (Button) findViewById(R.id.Button3A);
        mButton[2][1] = (Button) findViewById(R.id.Button3B);
        mButton[2][2] = (Button) findViewById(R.id.Button3C);
        mButton[2][3] = (Button) findViewById(R.id.Button3D);

        mButton[3][0] = (Button) findViewById(R.id.Button4A);
        mButton[3][1] = (Button) findViewById(R.id.Button4B);
        mButton[3][2] = (Button) findViewById(R.id.Button4C);
        mButton[3][3] = (Button) findViewById(R.id.Button4D);

        mButton[4][0] = (Button) findViewById(R.id.Button5A);
        mButton[4][1] = (Button) findViewById(R.id.Button5B);
        mButton[4][2] = (Button) findViewById(R.id.Button5C);
        mButton[4][3] = (Button) findViewById(R.id.Button5D);

        for (int row = 0; row < mButton.length; row++) {
            for (int col = 0; col < mButton[1].length; col++) {
                mButton[row][col].setOnClickListener(mButtonClicked);
            }
        }
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    private void gameStart() {
        printMole();

        if (mTimer != null) {
            return;
        }
        mTimer = new Timer(true);
        mTimer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        mGameTime--;
                        if (mGameTime <= 0) {
                            gameOver();
                        }
                        mTimeText.setText(Integer.toString(mGameTime));
                    }
                });
            }
        }, 1000, 1000);
    }

    private void gameOver() {
        mTimer.cancel();
        mTimer = null;
        mGameOver.setVisibility(View.VISIBLE);
    }

    @Override
    protected void onResume() {
        super.onResume();
        gameStart();
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    private void printMole() {
        if (mMoleButton != null) {
            mMoleButton.setBackgroundResource(R.drawable.bg_button);
        }
        int row = (int) (Math.random() * 5);
        int col = (int) (Math.random() * 4);
        mButton[row][col].setBackgroundResource(R.drawable.mole);
        mMoleButton = mButton[row][col];
    }

    private View.OnClickListener mButtonClicked = new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (view != mMoleButton) {
                return;
            }
            mScore++;
            String strScore = String.valueOf(mScore);
            mScoreText.setText(strScore);
            printMole();
        }
    };

    private View.OnClickListener mGameOverClicked = new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            mGameOver.setVisibility(View.INVISIBLE);
            mScore = 0;
            String strScore = String.valueOf(mScore);
            mScoreText.setText(strScore);
            mGameTime = 60;
            gameStart();
        }
    };
}