Hitung Luas Codes

activity_main.xml

<?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:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="io.github.sendz.hitungluas.MainActivity">

    <EditText
        android:id="@+id/edit_text_panjang"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="number"
        android:hint="Panjang" />

    <EditText
        android:id="@+id/edit_text_lebar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/edit_text_panjang"
        android:inputType="number"
        android:hint="Lebar" />

    <Button
        android:id="@+id/button_hitung"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/edit_text_lebar"
        android:text="Hitung"/>

</RelativeLayout>

MainActivity.java

package io.github.sendz.hitungluas;

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

public class MainActivity extends AppCompatActivity {
    private int panjang;
    private int lebar;
    private EditText inputPanjang;
    private EditText inputLebar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        inputPanjang = (EditText) findViewById(R.id.edit_text_panjang);
        inputLebar = (EditText) findViewById(R.id.edit_text_lebar);
        Button reset = (Button) findViewById(R.id.button_hitung);


        reset.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                panjang = Integer.valueOf(inputPanjang.getText().toString());
                lebar = Integer.valueOf(inputLebar.getText().toString());
                int luas = panjang * lebar;
                new AlertDialog.Builder(MainActivity.this).setTitle("Luas").setMessage(String.valueOf(luas)).show();
            }
        });
    }
}