Simple Interest Calculator in Android

SimpleInterest calculator in Android is developed to calculate the simple Interest in Android apps.

Android Studio Chipmunk is used to develop this project.

Simple interest formula is prt/100

activity_main.xml

The activity_main.xml file is an XML layout file used in Android app development. It defines the visual structure and components of the main user interface screen of the app.

This layout typically includes elements such as text fields, buttons, and labels, specifying their positions and attributes.

Created a TextView to show messages at the top.

Create a Number (decimal) field for the Principal amount and rate.

Take a Number field for Time.

Use a button and set its text to Calculate.

Take a TextView to show simple interest.

simple Interest calculation in android — simple Interest calculation in Android

Code layout is as below

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#F4E7E7"
    tools:context=".MainActivity">
    <TextView
        android:id="@+id/textView"
        android:layout_width="331dp"
        android:layout_height="42dp"
        android:layout_marginTop="40dp"
        android:background="#3F51B5"
        android:backgroundTint="#3F51B5"
        android:text="Simple Intrest Calculator"
        android:textAlignment="center"
        android:textColor="#F4F4F7"
        android:textSize="24sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <Button
        android:id="@+id/button"
        android:layout_width="214dp"
        android:layout_height="65dp"
        android:layout_marginTop="284dp"
        android:text="Calculate"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.492"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="52dp"
        android:text="TextView"
       android:textSize="24sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button" />
    <EditText
        android:id="@+id/editTextNumberDecimal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="112dp"
        android:ems="10"
        android:hint="Principal Amount"
        android:inputType="numberDecimal"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.492"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <EditText
        android:id="@+id/editTextNumberDecimal2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="168dp"
        android:ems="10"
        android:hint="Rate"
        android:inputType="numberDecimal"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <EditText
        android:id="@+id/editTextNumber4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="224dp"
        android:ems="10"
        android:hint="Time (in months)"
        android:inputType="number"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:background="#F4E7E7"

tools:context=".MainActivity">

<TextView

android:id="@+id/textView"

android:layout_width="331dp"

android:layout_height="42dp"

android:layout_marginTop="40dp"

android:background="#3F51B5"

android:backgroundTint="#3F51B5"

android:text="Simple Intrest Calculator"

android:textAlignment="center"

android:textColor="#F4F4F7"

android:textSize="24sp"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toTopOf="parent" />

<Button

android:id="@+id/button"

android:layout_width="214dp"

android:layout_height="65dp"

android:layout_marginTop="284dp"

android:text="Calculate"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintHorizontal_bias="0.492"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toTopOf="parent" />

<TextView

android:id="@+id/textView2"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="52dp"

android:text="TextView"

android:textSize="24sp"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintHorizontal_bias="0.498"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toBottomOf="@+id/button" />

<EditText

android:id="@+id/editTextNumberDecimal"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="112dp"

android:ems="10"

android:hint="Principal Amount"

android:inputType="numberDecimal"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintHorizontal_bias="0.492"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toTopOf="parent" />

<EditText

android:id="@+id/editTextNumberDecimal2"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="168dp"

android:ems="10"

android:hint="Rate"

android:inputType="numberDecimal"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintHorizontal_bias="0.497"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toTopOf="parent" />

<EditText

android:id="@+id/editTextNumber4"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="224dp"

android:ems="10"

android:hint="Time (in months)"

android:inputType="number"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintHorizontal_bias="0.497"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

The main activity in Java for Android is the entry point of an app. It manages UI components, and user interactions, and often initiates other activities or functions, making it a crucial part of app navigation and functionality.

create Textboxes and get its values using findViewById().

After getting values in the specified variable set the onClickListenert button.

the onclick listener will call calculateSimpleInterest() this method calculates the simple interest.

result.setAlpha(0.0f) is used to hide the result TextView at the start of the program.

At the method calculateSimpleIntrest() we set result.setAlpha(1.0f) to show the result TextView.

package com.ebhor.simpleinterest;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import java.text.DecimalFormat;

public class MainActivity extends AppCompatActivity {

    EditText principalEditText;
    EditText rateEditText;
    EditText timeEditText;
    Button calculateSI;
    TextView result;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        principalEditText = (EditText) findViewById(R.id.editTextNumberDecimal);
        rateEditText = (EditText) findViewById(R.id.editTextNumberDecimal2);
        timeEditText = (EditText) findViewById(R.id.editTextNumber4);
        calculateSI = (Button) findViewById(R.id.button);
        result = (TextView) findViewById(R.id.textView2);
        result.setAlpha(0.0f);
        calculateSI.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                calculateSimpleInterest();
            }
        });
    }

    public void calculateSimpleInterest() {
        Double principal = Double.parseDouble(principalEditText.getText().toString());
        Double rate = Double.parseDouble(rateEditText.getText().toString());
        Double time = Double.parseDouble(timeEditText.getText().toString());
        Double simpleInterest = principal * rate * time / 100;
        result.setText("Simple Interest: " + simpleInterest.toString());
        result.setAlpha(1.0f);
    }


}

package com.ebhor.simpleinterest;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

import java.text.DecimalFormat;

public class MainActivity extends AppCompatActivity {

EditText principalEditText;

EditText rateEditText;

EditText timeEditText;

Button calculateSI;

TextView result;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

principalEditText = (EditText) findViewById(R.id.editTextNumberDecimal);

rateEditText = (EditText) findViewById(R.id.editTextNumberDecimal2);

timeEditText = (EditText) findViewById(R.id.editTextNumber4);

calculateSI = (Button) findViewById(R.id.button);

result = (TextView) findViewById(R.id.textView2);

result.setAlpha(0.0f);

calculateSI.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View view) {

calculateSimpleInterest();

}

});

}

public void calculateSimpleInterest() {

Double principal = Double.parseDouble(principalEditText.getText().toString());

Double rate = Double.parseDouble(rateEditText.getText().toString());

Double time = Double.parseDouble(timeEditText.getText().toString());

Double simpleInterest = principal * rate * time / 100;

result.setText("Simple Interest: " + simpleInterest.toString());

result.setAlpha(1.0f);

}

Adding Validation in form

Validation in Android is essential to ensure that user inputs are correct and safe. It prevents errors, enhances user experience, and protects against security threats by verifying and controlling user-provided data.

Here we have added Saripaar validation library.

To add this library open build.gradle and under dependencies add implementation 'com.mobsandgeeks:android-saripaar:2.0.3' or any updated version of library.

MainActivity must implement Validator.ValidationListener and override two methods public void onValidationFailed(List errors) and public void onValidationSucceeded().

Working code is shown below.

package com.ebhor.simpleinterest;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.mobsandgeeks.saripaar.ValidationError;
import com.mobsandgeeks.saripaar.Validator;
import com.mobsandgeeks.saripaar.annotation.NotEmpty;

import java.text.DecimalFormat;
import java.util.List;

public class MainActivity extends AppCompatActivity implements Validator.ValidationListener {

    @NotEmpty(message = "Principal Amount Required")
    EditText principalEditText;
    @NotEmpty(message = "Rate Required")
    EditText rateEditText;
    @NotEmpty(message = "Time Required")
    EditText timeEditText;
    Button calculateSI;
    TextView result;
    Validator validator;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        principalEditText = (EditText) findViewById(R.id.editTextNumberDecimal);
        rateEditText = (EditText) findViewById(R.id.editTextNumberDecimal2);
        timeEditText = (EditText) findViewById(R.id.editTextNumber4);
        calculateSI = (Button) findViewById(R.id.button);
        result = (TextView) findViewById(R.id.textView2);
        result.setAlpha(0.0f);
        validator = new Validator(this);
        validator.setValidationListener(this);
        calculateSI.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                {
                    validator.validate();
                }
            }
        });
    }

    @Override
    public void onValidationSucceeded() {
        calculateSimpleInterest();
    }

    @Override
    public void onValidationFailed(List<ValidationError> errors) {
        for (ValidationError error : errors) {
            View view = error.getView();
            String message = error.getCollatedErrorMessage(this);

            // Display error messages ;)
            if (view instanceof EditText) {
                ((EditText) view).setError(message);
            } else {
                Toast.makeText(this, message, Toast.LENGTH_LONG).show();
            }
        }
    }

    public void calculateSimpleInterest() {
        Double principal = Double.parseDouble(principalEditText.getText().toString());
        Double rate = Double.parseDouble(rateEditText.getText().toString());
        Double time = Double.parseDouble(timeEditText.getText().toString());
        Double simpleInterest = principal * rate * time / 100;
        result.setText("Simple Interest: " + simpleInterest.toString());
        result.setAlpha(1.0f);
    }


}

package com.ebhor.simpleinterest;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

import android.widget.Toast;

import com.mobsandgeeks.saripaar.ValidationError;

import com.mobsandgeeks.saripaar.Validator;

import com.mobsandgeeks.saripaar.annotation.NotEmpty;

import java.text.DecimalFormat;

import java.util.List;

public class MainActivity extends AppCompatActivity implements Validator.ValidationListener {

@NotEmpty(message = "Principal Amount Required")

EditText principalEditText;

@NotEmpty(message = "Rate Required")

EditText rateEditText;

@NotEmpty(message = "Time Required")

EditText timeEditText;

Button calculateSI;

TextView result;

Validator validator;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

principalEditText = (EditText) findViewById(R.id.editTextNumberDecimal);

rateEditText = (EditText) findViewById(R.id.editTextNumberDecimal2);

timeEditText = (EditText) findViewById(R.id.editTextNumber4);

calculateSI = (Button) findViewById(R.id.button);

result = (TextView) findViewById(R.id.textView2);

result.setAlpha(0.0f);

validator = new Validator(this);

validator.setValidationListener(this);

calculateSI.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View view) {

{

validator.validate();

}

});

}

@Override

public void onValidationSucceeded() {

calculateSimpleInterest();

}

@Override

public void onValidationFailed(List<ValidationError> errors) {

for (ValidationError error : errors) {

View view = error.getView();

String message = error.getCollatedErrorMessage(this);

// Display error messages ;)

if (view instanceof EditText) {

((EditText) view).setError(message);

} else {

Toast.makeText(this, message, Toast.LENGTH_LONG).show();

}

public void calculateSimpleInterest() {

Double principal = Double.parseDouble(principalEditText.getText().toString());

Double rate = Double.parseDouble(rateEditText.getText().toString());

Double time = Double.parseDouble(timeEditText.getText().toString());

Double simpleInterest = principal * rate * time / 100;

result.setText("Simple Interest: " + simpleInterest.toString());

result.setAlpha(1.0f);

}

So here we have implemented Simple Interest Calculator in Android using validation.

Addition of two numbers in Android

Simple interest formula is p*r*t/100

activity_main.xml

MainActivity.java

Adding Validation in form

Read More

Simple interest formula is prt/100