Android Button represents a push-button. The android.widget.Button is subclass of TextView class and CompoundButton is the subclass of Button class.

There are different types of buttons in android such as RadioButton, ToggleButton, CompoundButton etc.

Here, we are going to create two textfields and one button for sum of two numbers. If user clicks button, sum of two input values is displayed on the Toast.

We can perform action on button using different types such as calling listener on button or adding onClick property of button in activity’s xml file.

 button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
               //code
            }
});
<Button
        android:onClick=“methodName”
/>

Drag the component or write the code for UI in activity_main.xml

First of all, drag 2 textfields from the Text Fields palette and one button from the Form Widgets palette as shown in the following figure.

android button example

The generated code for the ui components will be like this:

File: activity_main.xml
<?xml version=“1.0” encoding=“utf-8”?>
<RelativeLayout 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”
    tools:context=“example.javatpoint.com.sumoftwonumber.MainActivity”>
    <EditText
        android:id=“@+id/editText1”
        android:layout_width=“wrap_content”
        android:layout_height=“wrap_content”
        android:layout_alignParentTop=“true”
        android:layout_centerHorizontal=“true”
        android:layout_marginTop=“61dp”
        android:ems=“10”
        android:inputType=“number”
        tools:layout_editor_absoluteX=“84dp”
        tools:layout_editor_absoluteY=“53dp” />
    <EditText
        android:id=“@+id/editText2”
        android:layout_width=“wrap_content”
        android:layout_height=“wrap_content”
        android:layout_below=“@+id/editText1”
        android:layout_centerHorizontal=“true”
        android:layout_marginTop=“32dp”
        android:ems=“10”
        android:inputType=“number”
        tools:layout_editor_absoluteX=“84dp”
        tools:layout_editor_absoluteY=“127dp” />
    <Button
        android:id=“@+id/button”
        android:layout_width=“wrap_content”
        android:layout_height=“wrap_content”
        android:layout_below=“@+id/editText2”
        android:layout_centerHorizontal=“true”
        android:layout_marginTop=“109dp”
        android:text=“ADD”
        tools:layout_editor_absoluteX=“148dp”
        tools:layout_editor_absoluteY=“266dp” />
</RelativeLayout>

Activity class

Now write the code to display the sum of two numbers.

File: MainActivity.java
package example.javatpoint.com.sumoftwonumber;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
    private EditText edittext1, edittext2;
    private Button buttonSum;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
       addListenerOnButton();
    }
    public void addListenerOnButton() {
        edittext1 = (EditText) findViewById(R.id.editText1);
        edittext2 = (EditText) findViewById(R.id.editText2);
        buttonSum = (Button) findViewById(R.id.button);
        buttonSum.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String value1=edittext1.getText().toString();
                String value2=edittext2.getText().toString();
                int a=Integer.parseInt(value1);
                int b=Integer.parseInt(value2);
                int sum=a+b;
                Toast.makeText(getApplicationContext(),String.valueOf(sum), Toast.LENGTH_LONG).show();
            }
        });
    }
}

Output:

android button example 2