If you’re new to Android app development using Java, understanding how to properly write classes, methods, and variables is fundamental. These building blocks define how your app functions and interacts with data. This guide will break everything down into simple explanations and examples.

What is a Class in Java?

A class in Java is like a blueprint for creating objects. It can contain fields (variables) and methods (functions) to define the behavior of the object.

Example:

public class Car {
    String color;
    int speed;

    void drive() {
        System.out.println("The car is driving.");
    }
}

What is a Method in Java?

A method is a block of code that performs a specific task. Methods are defined inside classes and can be called from other parts of the code.

Example:

public void startEngine() {
    System.out.println("Engine started");
}

What is a Variable in Java?

Variables are containers for storing data values. Each variable has a data type, a name, and can hold a value.

Example:

String carName = "Toyota";
int carSpeed = 120;

Putting It All Together

Here is how you might use a class, method, and variables together in an Android Java app.

package com.aliendroid.myapplication;

import android.os.Bundle;
import android.util.Log;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

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

        Car myCar = new Car();
        myCar.color = "Red";
        myCar.speed = 100;
        myCar.drive();
    }

    class Car {
        String color;
        int speed;

        void drive() {
            Log.d("CarInfo", "Driving " + color + " car at speed " + speed + " km/h");
        }
    }
}

Best Practices

• • Use camelCase for method and variable names.
  • Class names should use PascalCase.
  • Keep your methods short and focused on one task.
  • Always initialize variables before using them.

Conclusion

Mastering how to write classes, methods, and variables in Java is the foundation for building powerful Android apps. Start practicing simple examples in Android Studio, and you’ll soon be able to build your own custom features.