How to build a simple Calculator app using Android Studio? (original) (raw)
Last Updated : 12 Jul, 2025
Create a simple calculator which can perform basic arithmetic operations like addition, subtraction, multiplication, or division depending upon the user input. A sample video is given below to get an idea about what we are going to do in this article.
Note that we are going to implement this project using the **Java language.
**Pre-requisites:
- Android App Development Fundamentals for Beginners
- Guide to Install and Set up Android Studio
- Android | Starting with the first app/android project
- Android | Running your first Android app
**Step-by-Step Implementation
Building a calculator app is a great starting project for Android beginners.
**Step 1: Create a New Project
To Create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio.
Note that select **Java as the programming language.
Directory Structure of the application is attached below:
**Step 2: Working with the activity_main.xml file
Navigate to the **app > res > layout > activity_main.xml and add the below code to that file.
**Below is the code for the activity_main.xml file:
acitivity_main.xml `
<EditText
android:id="@+id/editText2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:textAlignment="center"
android:focusable="false"
android:focusableInTouchMode="false"
android:layout_marginTop="40sp"
android:textSize="30dp"
android:hint="Enter the Value" />
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_marginTop="16dp"
android:orientation="horizontal">
<TextView
android:id="@+id/result"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="20sp"
android:text="Result: " />
<TextView
android:id="@+id/resultText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="20sp"
android:text="0" />
</LinearLayout>
<TableLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="16dp">
<TableRow
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center">
<Button
android:id="@+id/num1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="1" />
<Button
android:id="@+id/num2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="2" />
<Button
android:id="@+id/num3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="3" />
<Button
android:id="@+id/add"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/light_grey"
android:textSize="15sp"
android:textColor="@color/black"
android:text="+" />
</TableRow>
<TableRow
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center">
<Button
android:id="@+id/num4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="4" />
<Button
android:id="@+id/num5"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="5" />
<Button
android:id="@+id/num6"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="6" />
<Button
android:id="@+id/sub"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/light_grey"
android:textSize="15sp"
android:textColor="@color/black"
android:text="-" />
</TableRow>
<TableRow
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center">
<Button
android:id="@+id/num7"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="7" />
<Button
android:id="@+id/num8"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="8" />
<Button
android:id="@+id/num9"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="9" />
<Button
android:id="@+id/mul"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/light_grey"
android:textSize="15sp"
android:textColor="@color/black"
android:text="X" />
</TableRow>
<TableRow
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center">
<Button
android:id="@+id/dot"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/light_grey"
android:textSize="15sp"
android:textColor="@color/black"
android:text="." />
<Button
android:id="@+id/zero"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="0" />
<Button
android:id="@+id/clear_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/light_grey"
android:textSize="15sp"
android:textColor="@color/black"
android:text="CE" />
<Button
android:id="@+id/div"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/light_grey"
android:textSize="15sp"
android:textColor="@color/black"
android:text="/" />
</TableRow>
</TableLayout>
<Button
android:id="@+id/submit"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="40dp"
android:backgroundTint="@color/yellow"
android:textSize="15sp"
android:textColor="@color/black"
android:text="Submit" />`
After using this code the UI will be like as follows:
**Step 3: Working with the **MainActivity.java file
Below is the code for the **MainActivity.java file.
**MainActivity.java:
MainActivity.java `
package com.gfg.calculator_java;
import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity {
private EditText editText;
private TextView resultText;
private Button addButton, subtractButton, multiplyButton, divideButton, equalButton, clearButton;
private Button num1Button, num2Button, num3Button, num4Button;
private Button num5Button, num6Button, num7Button, num8Button, num9Button, zeroButton, dotButton;
private double num1, num2;
private boolean isAddition, isSubtraction, isMultiplication, isDivision;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editText = findViewById(R.id.editText2);
resultText = findViewById(R.id.resultText);
clearButton = findViewById(R.id.clear_text);
addButton = findViewById(R.id.add);
subtractButton = findViewById(R.id.sub);
multiplyButton = findViewById(R.id.mul);
divideButton = findViewById(R.id.div);
equalButton = findViewById(R.id.submit);
num1Button = findViewById(R.id.num1);
num2Button = findViewById(R.id.num2);
num3Button = findViewById(R.id.num3);
num4Button = findViewById(R.id.num4);
num5Button = findViewById(R.id.num5);
num6Button = findViewById(R.id.num6);
num7Button = findViewById(R.id.num7);
num8Button = findViewById(R.id.num8);
num9Button = findViewById(R.id.num9);
zeroButton = findViewById(R.id.zero);
dotButton = findViewById(R.id.dot);
addButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (editText.getText().length() > 0) {
num1 = Double.parseDouble(editText.getText().toString());
isAddition = true;
// Clear the EditText for the next number
editText.setText("");
}
}
});
subtractButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (editText.getText().length() > 0) {
num1 = Double.parseDouble(editText.getText().toString());
isSubtraction = true;
// Clear the EditText for the next number
editText.setText("");
}
}
});
multiplyButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (editText.getText().length() > 0) {
num1 = Double.parseDouble(editText.getText().toString());
isMultiplication = true;
// Clear the EditText for the next number
editText.setText("");
}
}
});
divideButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (editText.getText().length() > 0) {
num1 = Double.parseDouble(editText.getText().toString());
isDivision = true;
// Clear the EditText for the next number
editText.setText("");
}
}
});
clearButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText("");
resultText.setText("0");
// Reset all flags
isAddition = false;
isSubtraction = false;
isMultiplication = false;
isDivision = false;
}
});
equalButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (editText.getText().length() > 0) {
num2 = Double.parseDouble(editText.getText().toString());
if (isAddition) {
resultText.setText(String.valueOf(num1 + num2));
} else if (isSubtraction) {
resultText.setText(String.valueOf(num1 - num2));
} else if (isMultiplication) {
resultText.setText(String.valueOf(num1 * num2));
} else if (isDivision) {
if (num2 != 0) {
resultText.setText(String.valueOf(num1 / num2));
} else {
resultText.setText("Error");
}
}
// Reset all flags
isAddition = false;
isSubtraction = false;
isMultiplication = false;
isDivision = false;
}
}
});
num1Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "1");
}
});
num2Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "2");
}
});
num3Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "3");
}
});
num4Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "4");
}
});
num5Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "5");
}
});
num6Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "6");
}
});
num7Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "7");
}
});
num8Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "8");
}
});
num9Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "9");
}
});
zeroButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
editText.setText(editText.getText().toString() + "0");
}
});
dotButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (!editText.getText().toString().contains(".")) {
editText.setText(editText.getText().toString() + ".");
}
}
});
}}
`
Explanation of the above Program:
- The app initializes buttons for numbers (0-9), operations (add, subtract, multiply, divide), clear, equal, and dot.
- Number buttons append their value to the EditText for user input.
- Operation buttons store the first number (num1), set the corresponding operation flag, and clear EditText.
- The dot button adds a decimal point if it doesn’t already exist in the input.
- The equal button performs the operation with the second number (num2) and displays the result in TextView.
- The clear button resets the EditText and result, clearing operation flags.
- The app handles basic arithmetic operations and division by zero errors.