Android simple calculator

From this tutorial you will learn how to develop a Simple Calculator.This Calculator takes two numbers as input and performs Addition ,Subtraction , multiplication and Division, and the result is displayed. In this tutorial we are using-

3 EditText , 2 for collecting input  and the other to display output.
2 Textviews- To locate the EditText.
4 Buttons -Addition ,Subtraction , multiplication and Division.

Here is the full code for the program,

Application Name : SimpleCalculator
Project Name :  SimpleCalculator

Activity Name : MainActivity.java
Layout Name : activity_main.xml

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent" >

    <TextView

        android:id="@+id/textView1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentTop="true"

        android:layout_centerHorizontal="true"

        android:layout_marginTop="21dp"

        android:text="Enter First No : "

        android:textAppearance="?android:attr/textAppearanceLarge" />

    <EditText

        android:id="@+id/editText1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@+id/textView1"

        android:layout_centerHorizontal="true"

        android:layout_marginTop="22dp"

        android:ems="10" >

        <requestFocus />

    </EditText>

    <TextView

        android:id="@+id/textView2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@+id/editText1"

        android:layout_centerHorizontal="true"

        android:layout_marginTop="49dp"

        android:text="Enter Second No : "

        android:textAppearance="?android:attr/textAppearanceLarge" />

    <EditText

        android:id="@+id/editText2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignLeft="@+id/editText1"

        android:layout_below="@+id/textView2"

        android:layout_marginTop="45dp"

        android:ems="10" />

    <EditText

        android:id="@+id/editText3"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_above="@+id/button2"

        android:layout_alignLeft="@+id/editText2"

        android:layout_marginBottom="37dp"

        android:ems="10" />

    <Button

        android:id="@+id/button1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentBottom="true"

        android:layout_alignParentLeft="true"

        android:layout_marginBottom="17dp"

        android:text="+" />

    <Button

        android:id="@+id/button3"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignBaseline="@+id/button2"

        android:layout_alignBottom="@+id/button2"

        android:layout_alignRight="@+id/textView1"

        android:layout_marginRight="14dp"

        android:text="*" />

    <Button

        android:id="@+id/button4"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignBaseline="@+id/button3"

        android:layout_alignBottom="@+id/button3"

        android:layout_toRightOf="@+id/button3"

        android:text="/" />

    <Button

        android:id="@+id/button2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignBaseline="@+id/button1"

        android:layout_alignBottom="@+id/button1"

        android:layout_alignLeft="@+id/textView1"

        android:text="-" />

</RelativeLayout>

MainActivity.java 

package com.example.simplecalculator;

import android.os.Bundle;

import android.app.Activity;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.EditText;

import android.widget.Toast;

public class MainActivity extends Activity {

Button plus,sub,mult,div;

EditText fno,sno,result;

int a,b,c;

String m,n;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

plus=(Button)findViewById(R.id.button1);

sub=(Button)findViewById(R.id.button2);

fno=(EditText)findViewById(R.id.editText1);

sno=(EditText)findViewById(R.id.editText2);

result=(EditText)findViewById(R.id.editText3);

plus.setOnClickListener(new OnClickListener() {

public void onClick(View v) {

// TODO Auto-generated method stub

String m=fno.getText().toString();

String n=sno.getText().toString();

if( m.equals("")||(n.equals("")))

{

Toast.makeText(getApplicationContext(), "Enter Both Numbers",Toast.LENGTH_SHORT).show();

}

else

{

a=Integer.parseInt(m);

b=Integer.parseInt(n);

c=a+b;

result.setText(Integer.toString(c));

}

}

});

sub=(Button)findViewById(R.id.button2);

sub.setOnClickListener(new OnClickListener() {

public void onClick(View v) {

// TODO Auto-generated method stub

String m=fno.getText().toString();

String n=sno.getText().toString();

if( m.equals("")||(n.equals("")))

{

Toast.makeText(getApplicationContext(), "Enter Both Numbers",Toast.LENGTH_SHORT).show();

}

else

{

a=Integer.parseInt(m);

b=Integer.parseInt(n);

c=a-b;

result.setText(Integer.toString(c));

}

}

});

mult=(Button)findViewById(R.id.button3);

mult.setOnClickListener(new OnClickListener() {

public void onClick(View v) {

// TODO Auto-generated method stub

String m=fno.getText().toString();

String n=sno.getText().toString();

if( m.equals("")||(n.equals("")))

{

Toast.makeText(getApplicationContext(), "Enter Both Numbers",Toast.LENGTH_SHORT).show();

}

else

{

a=Integer.parseInt(m);

b=Integer.parseInt(n);

c=a*b;

result.setText(Integer.toString(c));

}

}

});

div=(Button)findViewById(R.id.button4);

div.setOnClickListener(new OnClickListener() {

public void onClick(View v) {

// TODO Auto-generated method stub

String m=fno.getText().toString();

String n=sno.getText().toString();

if( m.equals("")||(n.equals("")))

{

Toast.makeText(getApplicationContext(), "Enter Both The Numbers",Toast.LENGTH_SHORT).show();

}

else

{

a=Integer.parseInt(m);

b=Integer.parseInt(n);

c=a/b;

result.setText(Integer.toString(c));

}

}

});

}

}

When user presses the Button without entering the values,there is a chance of getting an application error, to avoid this the following code is used above

if( m.equals("")||(n.equals("")))

{

Toast.makeText(getApplicationContext(), "Enter Both The Numbers",Toast.LENGTH_SHORT).show();

}

The Output of the application is like this :