Java Android Development

Required Tools

# Install JDK 8 or higher
# Download from Oracle or use OpenJDK

# Verify installation
java -version
javac -version

MainActivity.java

package com.example.myapp;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private TextView textView;
    private Button button;
    private int counter = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        // Initialize views
        textView = findViewById(R.id.textView);
        button = findViewById(R.id.button);
        
        // Set click listener
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                counter++;
                textView.setText("Count: " + counter);
                Toast.makeText(MainActivity.this, 
                    "Button clicked!", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    android:padding="16dp">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Count: 0"
        android:textSize="24sp"
        android:layout_marginBottom="32dp" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click Me"
        android:textSize="18sp"
        android:padding="16dp" />

</LinearLayout>