/** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        //Get the Button and the TextView from the Resource class
        Button btn = (Button)this.findViewById(R.id.button1); //needs import android.widget.Button;

        //Final in java can only be initialized once this is necessary to for use in inner method
        final TextView tv = (TextView)this.findViewById(R.id.textView1);  //needs import android.widget.TextView;
        String s = "hello";
        tv.setText(s);
    }

btn.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				tv.setText(d.About());
			}
		});

public void buttonPressMe_OnCLick(View v)
    {
        TextView tv = (TextView)this.findViewById(R.id.textView2);
        tv.setText("Hello From Button!!");
    }

<Button
        android:text="Press Me"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginLeft="13dp"
        android:layout_marginStart="13dp"
        android:layout_marginTop="24dp"
        android:id="@+id/buttonPressMe"
        android:onClick="buttonPressMe_OnCLick (MainActivity)" />

public class Dog {
    public String Name; //Java uses capital S String
    public int Weight;
    public String BarkSound;

    //Constructor
    public Dog()
    {
        this.Name = "fido";
        this.Weight = 1;
        this.BarkSound = "woof";
    }

    public void Eat()
    {
        this.Weight++;
    }
    public void Poop()
    {
        this.Weight--;
    }

    public String About()
    {
        //Java string.format is similar to c# but used %s for string substitution
        return String.format("Hello my name is %s. I weigh %s lbs",
                this.Name, this.Weight);
    }
}