In this article we are going to create a calculator Android App using Android Studio. This application will perform the basic arithmetic operations like addition, subtraction, multiplication, division, and modulo.
Let’s get started
Step 1: Create a new project
- Open a new android project and select Empty Activity and click on Next.
- Give name as “Calculator” or whatever name you want.
- Choose a file location and select language as Java and click on next.
- Finally click on Finish.
Step 2: Designing the UI
In activity_main.xml remove the Hello World text and change the layout to LinearLayout.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
tools:context=".MainActivity">
</LinearLayout>
Drag and drop the Plain Text into the UI
<EditText
android:id="@+id/editText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="textPersonName"
android:layout_marginBottom="1pt"
android:layout_weight="1"
android:background="@color/purple_200"
android:gravity="right|center"
android:textSize="40pt"
android:textColor="@color/white"
android:text="0" />
Now drag and drop the TableLayout into the UI design.
<TableLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/buAc"
android:text="AC"
android:onClick="acEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buPlusMinus"
android:text="+/-"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buDivide"
android:text="/"
android:onClick="operatorEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buMulti"
android:text="x"
android:onClick="operatorEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/design_default_color_primary_dark"
></Button>
</TableRow>
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/bu7"
android:text="7"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu8"
android:text="8"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu9"
android:text="9"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buPercentage"
android:text="%"
android:onClick="percentageEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/design_default_color_primary_dark"
></Button>
</TableRow>
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/bu4"
android:text="4"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu5"
android:text="5"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu6"
android:text="6"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buPlus"
android:text="+"
android:onClick="operatorEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/design_default_color_primary_dark"
></Button>
</TableRow>
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/bu1"
android:text="1"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu2"
android:text="2"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu3"
android:text="3"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buMuins"
android:text="-"
android:onClick="operatorEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/design_default_color_primary_dark"
></Button>
</TableRow>
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/bu0"
android:text="0"
android:onClick="numberEvent"
android:layout_weight="5"
android:layout_width="46pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buDot"
android:text="."
android:onClick="numberEvent"
android:layout_weight="4"
android:layout_width="46pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buEqual"
android:text="="
android:onClick="equalEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
</TableRow>
</TableLayout>
Copy the below code and paste it into the activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
tools:context=".MainActivity">
<EditText
android:id="@+id/editText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="textPersonName"
android:layout_marginBottom="1pt"
android:layout_weight="1"
android:background="@color/purple_200"
android:gravity="right|center"
android:textSize="40pt"
android:textColor="@color/white"
android:text="0" />
<TableLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/buAc"
android:text="AC"
android:onClick="acEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buPlusMinus"
android:text="+/-"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buDivide"
android:text="/"
android:onClick="operatorEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buMulti"
android:text="x"
android:onClick="operatorEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/design_default_color_primary_dark"
></Button>
</TableRow>
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/bu7"
android:text="7"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu8"
android:text="8"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu9"
android:text="9"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buPercentage"
android:text="%"
android:onClick="percentageEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/design_default_color_primary_dark"
></Button>
</TableRow>
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/bu4"
android:text="4"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu5"
android:text="5"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu6"
android:text="6"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buPlus"
android:text="+"
android:onClick="operatorEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/design_default_color_primary_dark"
></Button>
</TableRow>
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/bu1"
android:text="1"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu2"
android:text="2"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/bu3"
android:text="3"
android:onClick="numberEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buMuins"
android:text="-"
android:onClick="operatorEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/design_default_color_primary_dark"
></Button>
</TableRow>
<TableRow
android:layout_marginBottom="1pt"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/bu0"
android:text="0"
android:onClick="numberEvent"
android:layout_weight="5"
android:layout_width="46pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buDot"
android:text="."
android:onClick="numberEvent"
android:layout_weight="4"
android:layout_width="46pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
<Button
android:id="@+id/buEqual"
android:text="="
android:onClick="equalEvent"
android:layout_weight="1"
android:layout_width="30pt"
android:layout_height="30pt"
android:layout_marginRight="1pt"
android:background="@color/lightblack"
></Button>
</TableRow>
</TableLayout>
</LinearLayout>
After that the UI will look like this

Step 3: Working with Java file
Declare these variables,
EditText et1;
boolean isNewOp = true;
String op = "+";
String Oldval;
We have created five events and they are,
- numberEvent
- operatorEvent
- equalEvent
- acEvent
- percentageEvent
numberEvent
This event will display the number when we click on the particular number,
public void numberEvent(View view) {
if (isNewOp)
et1.setText("");
isNewOp = false;
String number = et1.getText().toString();
switch (view.getId()){
case R.id.bu7:
number += "7";
break;
case R.id.bu8:
number += "8";
break;
case R.id.bu9:
number += "9";
break;
case R.id.bu4:
number += "4";
break;
case R.id.bu5:
number += "5";
break;
case R.id.bu6:
number += "6";
break;
case R.id.bu1:
number += "1";
break;
case R.id.bu2:
number += "2";
break;
case R.id.bu3:
number += "3";
break;
case R.id.bu0:
number += "0";
break;
case R.id.buDot:
number += ".";
break;
case R.id.buPlusMinus:
number = "-"+number;
break;
}
et1.setText(number);
}
operatorEvent
This event will perform mathematical operations when we click on the particular operator,
public void operatorEvent(View view) {
isNewOp = true;
Oldval = et1.getText().toString();
switch (view.getId()){
case R.id.buDivide:
op = "/";
break;
case R.id.buMulti:
op = "*";
break;
case R.id.buPlus:
op = "+";
break;
case R.id.buMuins:
op = "-";
break;
}
}
equalEvent
This event will give the result,
public void equalEvent(View view) {
String newNum = et1.getText().toString();
double result = 0.0;
switch (op){
case "+":
result = Double.parseDouble(Oldval) + Double.parseDouble(newNum);
break;
case "-":
result = Double.parseDouble(Oldval) - Double.parseDouble(newNum);
break;
case "/":
result = Double.parseDouble(Oldval) / Double.parseDouble(newNum);
break;
case "*":
result = Double.parseDouble(Oldval) * Double.parseDouble(newNum);
break;
}
et1.setText(result+"");
}
acEvent
This event will clear the result,
public void acEvent(View view) {
et1.setText("0");
isNewOp = true;
}
percentageEvent
This event will gives the modulo result,
public void percentageEvent(View view) {
double no = Double.parseDouble(et1.getText().toString())/100;
et1.setText(no +"");
isNewOp = true;
}
Now copy and paste the below code in MainActivity.java
package com.neuralbeast.calculator;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
public class MainActivity extends AppCompatActivity {
EditText et1;
boolean isNewOp = true;
String op = "+";
String Oldval;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
et1 = (EditText)findViewById(R.id.editText);
}
public void numberEvent(View view) {
if (isNewOp)
et1.setText("");
isNewOp = false;
String number = et1.getText().toString();
switch (view.getId()){
case R.id.bu7:
number += "7";
break;
case R.id.bu8:
number += "8";
break;
case R.id.bu9:
number += "9";
break;
case R.id.bu4:
number += "4";
break;
case R.id.bu5:
number += "5";
break;
case R.id.bu6:
number += "6";
break;
case R.id.bu1:
number += "1";
break;
case R.id.bu2:
number += "2";
break;
case R.id.bu3:
number += "3";
break;
case R.id.bu0:
number += "0";
break;
case R.id.buDot:
number += ".";
break;
case R.id.buPlusMinus:
number = "-"+number;
break;
}
et1.setText(number);
}
public void operatorEvent(View view) {
isNewOp = true;
Oldval = et1.getText().toString();
switch (view.getId()){
case R.id.buDivide:
op = "/";
break;
case R.id.buMulti:
op = "*";
break;
case R.id.buPlus:
op = "+";
break;
case R.id.buMuins:
op = "-";
break;
}
}
public void equalEvent(View view) {
String newNum = et1.getText().toString();
double result = 0.0;
switch (op){
case "+":
result = Double.parseDouble(Oldval) + Double.parseDouble(newNum);
break;
case "-":
result = Double.parseDouble(Oldval) - Double.parseDouble(newNum);
break;
case "/":
result = Double.parseDouble(Oldval) / Double.parseDouble(newNum);
break;
case "*":
result = Double.parseDouble(Oldval) * Double.parseDouble(newNum);
break;
}
et1.setText(result+"");
}
public void acEvent(View view) {
et1.setText("0");
isNewOp = true;
}
public void percentageEvent(View view) {
double no = Double.parseDouble(et1.getText().toString())/100;
et1.setText(no +"");
isNewOp = true;
}
}
Download Project
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