Working with Button

activity_main.xml:

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

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

    android:id="@+id/LinearLayout1"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical"

    tools:context=".MainActivity" >

    

    <Button 

        android:id="@+id/clickButton"

        android:layout_height="wrap_content"

        android:layout_width="wrap_content"

        android:text="Click Me"

        android:layout_gravity="center"

        android:layout_marginTop="50dp"

        android:textSize="20dp"

        />

    

</LinearLayout>

public class MainActivity extends Activity implements OnClickListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);


Button clickBtn = (Button)findViewById(R.id.clickButton);

clickBtn.setOnClickListener(this);
}

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(), "button is working", Toast.LENGTH_LONG).show();
}

}

Working with Button(Anonymous Inner Type):

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/clickMeButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="111dp"
        android:layout_marginTop="54dp"
        android:text="Click Me" />

</RelativeLayout>

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    
    Button clickButton = (Button)findViewById(R.id.clickMeButton);
    
    
    clickButton.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(), "button is working", 3000).show();
}
});
    
    
    }
}

Working with Multiple Buttons:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="104dp"
        android:layout_marginTop="20dp"
        android:text="Button1" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/button1"
        android:layout_below="@+id/button1"
        android:layout_marginTop="34dp"
        android:text="Button2" />

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/button2"
        android:layout_centerVertical="true"
        android:text="Button3" />

    <Button
        android:id="@+id/button4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/button3"
        android:layout_below="@+id/button3"
        android:layout_marginTop="34dp"
        android:text="Button4" />

    <Button
        android:id="@+id/button5"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/button4"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="24dp"
        android:text="Button5" />

</RelativeLayout>

public class MainActivity extends Activity implements OnClickListener {
Button b1,b2,b3,b4,b5;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        b1 = (Button)findViewById( R.id.button1);
        b2 = (Button)findViewById(R.id.button2);
        b3 = (Button)findViewById(R.id.button3);
        b4 = (Button)findViewById(R.id.button4);
        b5 = (Button)findViewById(R.id.button5);
     
        
        
        b1.setOnClickListener(this);
        b2.setOnClickListener(this);
        b3.setOnClickListener(this);
        b4.setOnClickListener(this);
        b5.setOnClickListener(this);

    }

@Override
public void onClick(View v) {

switch (v.getId()) {
case R.id.button1:
Toast.makeText(getApplicationContext(), "button1 is working", 3000).show();
break;

case R.id.button2:
Toast.makeText(getApplicationContext(), "button2 is working", 3000).show();
break;

case R.id.button3:
Toast.makeText(getApplicationContext(), "button3 is working", 3000).show();
break;

case R.id.button4:
Toast.makeText(getApplicationContext(), "button4 is working", 3000).show();
break;

case R.id.button5:
Toast.makeText(getApplicationContext(), "button5 is working", 3000).show();
break;
}

}
}