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How to build a simple Calculator app using Android Studio?

Last Updated : 24 Apr, 2025
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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. 

How-to-build-a-simple--Calculator-app--using-Android-Studio_


Pre-requisites:  

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:

Directory_Structure


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 
<?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:background="@color/white"
    android:gravity="center"
    android:padding="16dp">

    <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" />
</LinearLayout>

After using this code the UI will be like as follows:

Layout


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.

Output:




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